Rozprawy doktorskie na temat „SOLID STATE LIGHTING (SSL)”

The objective of the research was to develop high quality GaN epitaxial growth on alternative substrates that could result in higher external quantum efficiency devices. Typical GaN growth on sapphire results in high defect materials, typically 10⁸⁻¹⁰cm⁻², due to a large difference in lattice mismatch and thermal expansion coefficient. Therefore, it is useful to study epitaxial growth on alternative substrates to sapphire such as ZnO which offers the possibility of lattice matched growth. High-quality metalorganic chemical vapor deposition (MOCVD) of GaN on ZnO substrate is hard to grow due to the thermal stability of ZnO, out-diffusion of Zn, and H₂back etching into the sample. Preliminary growths of GaN on bare ZnO substrates showed multiple cracks and peeling of the surface. A multi-buffer layer of LT-AlN/GaN was found to solve the cracking and peeling-off issues and demonstrated the first successful GaN growth on ZnO substrates. Good quality InGaN films were also grown showing indium compositions of 17-27% with no indium droplets or phase separation. ZnO was found to to sustain a higher strain state than sapphire, and thereby incorporating higher indium concentrations, as high as 43%, without phase separation, compared to the same growth on sapphire with only 32%. Si doping of InGaN layers, a known inducer for phase separation, did induce phase separation on sapphire growths, but not for growths on ZnO. This higher strain state for ZnO substrates was correlated to its perfect lattice match with InGaN at 18% indium concentration. Transmission electron microscopy results revealed reduction of threading dislocation and perfectly matched crystals at the GaN buffer/ZnO interface showing coherent growth of GaN on ZnO. However, Zn diffusion into the epilayer was an issue. Therefore, an atomic layer deposition of Al₂O₃was grown as a transition layer prior to GaN and InGaN growth by MOCVD. X-ray and PL showed distinct GaN peaks on Al₂O₃/ZnO layers demonstrating the first GaN films grown on Al₂O₃/ZnO. X-ray photoelectron spectroscopy showed a decrese in Zn diffusion into the epilayer, demonstrating that an ALD Al₂O₃layer was a promising transition layer for GaN growth on ZnO substrates by MOCVD.

Nowadays research in the field of lighting technology is directed toward conversion of electrical energy into visible light to ensure greater energy savings. More recent research has addressed the production of LED lamps as an alternative to compact fluorescent lamps (CFL). LED lamps offer a different technology for the direct conversion of the electrical energy into visible light. The industrial interest is now directed towards the development and production of LED lamps for their remarkable features: the high energy saving, control of brightness and color and a long operating life. This thesis studies such lighting technology, provides the principles of dimensioning of the supply circuit of an LED lamp, and develops a comparison between the two different technologies, by tracing of technical and economic comparisons, and identifying the various technical parameters through laboratory measurements and a detailed analysis.

Recent advances in solid state lighting (SSL) technology have encouraged its utilization in versatile applications. SSL technology based on phosphor converted light emitting diodes (pc-LEDs) are acting potentially as a substitute for traditional incandescent and fluorescent lamps on an account of their unprecedented luminous efficiency, low energy consumption, less emission of harmful gases, high brightness, compact design, fast switching and long working lifetimes. The pc-LEDs utilize phosphors coated on the LED chip capable of emitting light in desirable spectral regions upon an appropriate excitation. In the light of the above mentioned advantages, pc-LEDs are believed to be the next generation SSL technology and will bring a revolutionary changes in the lighting industry. For example, the white pc-LEDs have been the most preferred lighting devices for general illumination due to effective energy utilization, long lifetime, safety and so on. Moreover, pc-LEDs can be harnessed for indoor agricultural lighting owing to their excellence in controlling the spectral composition and lighting intensity to mimic the changes of sunlight during the day. Therefore, all the above mentioned fascinating features like effective energy saving and desirable light emission have enabled pc-LEDs to become economically feasible choice for general illumination and large scale indoor agricultural lighting applications around the corners of the world. The phosphor based w-LEDs can be developed by (i) coating of appropriate mixture of red, green and blue (RGB) phosphors excited with UV LED chip (ii) single yellow phosphor by a blue LED chip. However, reabsorption of blue color by RG phosphors in the former approach and lack of red component in later approach may lead to shortcomings like low color saturation, deteriorated color rendering index (CRI) and low color temperature stability. To overcome the above mentioned shortcomings, it is necessary to develop single phase phosphor doped with appropriate combination of rare earth ions (such as Dy3+/Eu3+, Tb3+/Eu3+ , Tb3+/Sm3+, Dy3+/Sm3+ etc.) providing white light emission via energy transfer or new red vii phosphor for the improvement of performance factors like luminous efficiency, CRI and correlated color temperature (CCT). Further, for plant growth under controlled environment fitted with smart pc-LEDs, it is necessary to conduct a widespread research for deep-red, far- red and blue light emitting phosphors that can be utilised to best drive photosynthetic metabolism and photo-morphogenesis as per the literature survey. Therefore, the ascending demand of energetically efficient lighting devices for general illumination and plant growth applications has led to a significant interest in the development of novel high quality phosphors with superior brightness, multiple emission color and excellent color purity. Besides lighting, the phosphors facilitate their utilization in diverse applications such as solar cells, bio-sensing and other optoelectronic devices due to their versatile physical, chemical and luminescent properties. In general, phosphor consisting of a host matrix (crystalline host) and an activator (luminescent center) have been pondered as a technologically significant components for the development of w-LEDs and agricultural lighting systems. In the past few decades, inorganic phosphors activated with rare earth (RE) ions have remained the prevalent protocol for fabricating pc-LEDs due to unique luminescence properties of RE ions. In such phosphors, the intermixing of oxygen atomic orbitals of host with orbitals of RE ion creates a specific crystal field environment around it such that transitions between incompletely filled 4f energy levels of RE ions deliver distinctive luminescence features. Also, the efficient energy transfer from the host crystal to the RE activators have been investigated to comprehend interesting optical phenomena. Among all the various inorganic oxides, vanadates have attracted acquiescent utilization in the wide-spread of luminescent device applications due to their wide-range of excitation wavelengths with abundant luminous colour, good physical and chemical stability. In addition, the vanadate materials are cost-effective and their preparation methods are energy efficient. The vanadate based phosphors give a broadband emission originating from inherent [VO4] 3- group. The broadband emission in the visible range by vanadate hosts can bring viii improvement in CRI and CCT values. Recent investigations have been established the possibility of achieving tunable visible emissions in RE activated vanadate phosphors via controlling [VO4] 3- to RE ions energy transfer. To harness the above mentioned precedencies, an investigation on a new ternary vanadate (CaBiVO5) phosphor doped with RE ions has been done for general and agricultural lighting applications. By incorporating suitable RE ions, the present host (CaBiVO5) can be tuned to emit different colors in the visible region suitable for pc-LEDs used in general illumination and agricultural lighting applications. Based on the extensive structural, morphological and photoluminescence characterizations, the outcome of the research work for accomplishing the research objectives has been organized in seven chapters. The brief summary of each chapter is as follows: Chapter 1 highlights the brief history, motivation, an outlook on the recent developments, potential challenges and great opportunities in white light generation and agricultural lighting. This chapter explains the basic concepts related to luminescence, spectroscopic features of RE ions, theoretical models implemented for examining the observed spectral data, and possible energy transfer processes. This chapter also present a brief viewpoint on the various characteristics and indices such as chromaticity coordinates, color purity, CCT and activation energy describing the color quality, thermal stability and performance of pc-LEDs. The importance of the present work and selected vanadate host have been discussed briefly in this chapter. At the last, the objectives of the thesis based on literature review have been included. Chapter 2 makes a thorough discussion about the different synthesis methods opted for the synthesis of single phase calcium bismuth vanadate (CaBiVO5: CBV) phosphors activated with different RE ions (Eu3+, Sm3+, Pr3+ and Dy3+). It also explicates the basic principle and working of experimental techniques employed to explore structural, morphological, optical and luminescent properties of CBV phosphors. The thermal and structural properties are studied by thermogravimetric analysis (TGA) and X-ray Diffraction (XRD) method, respectively. The ix scanning electron microscopy (SEM) reveals the morphology of the as synthesized phosphors. The optical properties are determined from diffuse-reflectance (DR) spectral measurements, while photoluminescence properties, thermal stability and decay kinetics of the CBV phosphors doped with different RE ions were investigated using spectrofluorophotometer. All these characterization techniques have been discussed in this chapter. Chapter 3 describes about the synthesis of single phase Eu3+ activated calcium bismuth vanadate (CaBiVO5) phosphors using solid state reaction method. X-ray diffraction (XRD) analysis confirms the pure phase formation and scanning electron microscope (SEM) micrographs exhibit inhomogeneous particle formation with irregular morphology of Eu3+ doped CaBiVO5 (CBV) phosphor. The photoluminescence excitation (PLE) spectrum indicates significant absorption in the ultraviolet (UV) and near ultraviolet (n-UV) spectral regions for un-doped CBV sample, whereas Eu 3+ doped CBV phosphors reveal various sharp absorption bands in n-UV and blue region along with host absorption bands. Trivalent europium activated CBV phosphors under 342 nm excitation exhibit dominant red emission peak at 613 nm wavelength accompanied by weak broadband originating from VO4 groups, whereas the phosphors under 464 nm excitation, exhibit similar emission profile with most intense one centered at 613 nm by excluding host emission bands. The energy transfer mechanism and the probable cause for concentration quenching beyond 4.0 mol% of Eu3+ ions concentration have been discussed in detail. The CIE chromaticity coordinates for the optimized phosphor, (0.551, 0.398) and (0.639, 0.358), situated in the reddish-orange and red region under 342 and 464 nm excitations, respectively. The CIE coordinates calculated based on the emission spectra measured under 464 nm excitation are close to the commercial phosphor Y2O2S: Eu3+ (0.622, 0.351). All the above mentioned results support the utilization of Eu3+ doped CBV phosphor as a potential red emitting component for luminescent devices. x The research work described in this chapter has been published in “Ceramics International 45 (2019) 15385-15393” (Impact factor =4.527) Chapter 4 describes the optimization of synthesis procedure for Sm3+ doped CaBiVO5 phosphor by preparing through it via three different synthesis methods, solid-state reaction (SR), combustion (CB) and citrate sol-gel (SG) method to enhance the luminescent properties. The pure phase formation of CBV: Sm3+ phosphors via diverse routes (SR, CB and SG) is confirmed as diffraction peaks for all prepared phosphors correspond to the standard data (JCPDS card no: 81-1775). The SEM results reveal that CBV: Sm3+ phosphors are synthesized with improved homogeneity and shape regularity at lower reaction temperature via SG method. The excitation spectra measured by monitoring the emission at 649 nm for CBV: Sm3+ phosphors reveal significant absorption in ultraviolet (UV), near (n)-UV and blue spectral regions. The comparative photoluminescence (PL) spectra measured under 343 nm excitation for differently synthesized CBV: Sm3+ phosphors, which exhibit significantly enhanced emission intensity for SG derived phosphor than other adopted methods. The PL spectra for SG derived 1.0 mol% Sm3+ doped CBV phosphor at λex = 275 and 343 nm exhibit sharp peaks located at 566, 606 and 649 nm along with weak host emission broadband and for λex = 406 nm, similar sharp peaks of Sm3+ transitions are observed without any host emission. Unlike mostly explored Sm3+ doped phosphors, emission peak in red spectral region (649 nm) is more intense as compared to the emission peak in orange region (599 nm) in the present work. The energy transfer mechanism responsible for concentration quenching in CBV phosphors is discussed in detail. The CBV: Sm3+ phosphors manifest color tunability from orange to orange- red region by modulating excitation from 275 nm (0.567, 0.404) to 343 nm (0.591, 0.399) and finally to 406 nm (0.620, 0.376). The temperature-dependent PL studies indicate appreciable thermal stability of as-prepared phosphor. Above mentioned results suggest that CBV: Sm3+ phosphor has great potential for use in white light-emitting diode (w-LED) applications. xi The research work described in this chapter has been published in “Optical Materials 107 (2020) 110119” (Impact factor =3.080). Chapter 5 describes the citrate sol-gel synthesis of Dy3+ activated and Dy3+/Eu3+ bi-activated calcium bismuth vanadate (CBV) phosphor to achieve white light emission and color- tunability. The phase purity and quasi-spherical particle with few agglomerations of the as- prepared CBV phosphors are indicated by structural and morphological characterizations, respectively. The emission spectral properties and energy transfer in Dy3+ doped and Dy3+/Eu3+ co-doped CBV phosphors have been examined extensively. The Dexter and Reisfeld’s approximation applied to emission spectra specifies electric dipolar-dipolar interaction to be accountable for Dy3+ to Eu3+ energy transfer. In CBV: Dy3+ phosphors, co-doping with Eu3+ ion facilitates red component that ensues warm white light emission as well as flexible color tunability with increasing Eu3+ ion concentration under different excitations. The significant findings like warm white light emission and controllable spectral composition in Dy3+/Eu3+ co- doped CBV phosphor by altering the excitation energy and co-dopant (Eu3+) concentration potentiate it as a suitable candidate in the domain of lighting and display devices. The research work described in this chapter is communicated to an Internationally reputed Journal “Solid State Sciences (2021)” (Impact factor = 3.059) Chapter 6 describes about orthorhombic Pr3+ -doped calcium bismuth vanadate (CBV: Pr3+) phosphors synthesized via citrate-gel method. The single-phase formation of CBV: Pr3+ phosphor has been endorsed by XRD analysis. The SEM image reveals dense-particle packaging with the quasi-spherical shape for the prepared CBV: Pr3+ phosphors. Under blue light excitation, CBV: Pr3+ phosphors exhibit intense red emission bands located at 608 and 656 nm wavelengths, overlapping with the absorption spectrum of PR phytochrome, which is present in plants. To achieve the maximum red intensity, the Pr3+ ion concentration is optimized xii to be 1.25 mol% in the CBV host, after which the emission intensity ceases due to the concentration quenching. Dexter's theory disclosed the possibility of d-d multipolar interaction among Pr3+ ions at higher concentrations of Pr3+ ions in the CBV host. The CIE coordinates are found to be positioned in the pure red region for CBV: Pr3+ phosphor and in the proximity of red-emitting commercial phosphor. The temperature dependent spectral studies manifest substantial thermal stability of the as-synthesized phosphor. All the studies mentioned above specify the tremendous potentiality of thermally stable CBV: Pr3+ phosphor in agricultural lighting and w-LED applications. The research work described in this chapter has been accepted to publish in “Journal of the American Ceramic Society 104 (2021) 5764-5775” (Impact factor =3.784). Chapter 7 summarizes the research outcomes of the work described in chapters 3 to 6 and outline the future scope of the thesis work for the expected applications.

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 142-148).
Energy conservation concerns will mandate near-future environments to regulate themselves to accommodate occupants' objectives and best tend to their comfort while minimizing energy consumption. Accordingly, smart energy management will be a needed and motivating application area of evolving Cyber-Physical Systems, as user state, behavior and context are measured, inferred, and leveraged across a variety of domains, environments, sensors, and actuators to dynamically mitigate energy usage while attaining implicit and explicit user goals. In this work, the focus in on the efficient control of a LED-based lighting network. This thesis presents a first-of-its-kind pentachromatic LED-based lighting network that is capable of adjusting its spectral output in response to ambient conditions and the user's preferences. The control of the intensity is formulated as a nonlinear optimization problem and the mathematics governing sensed illuminance, color, and corresponding control (feedback and adjustment) are formally defined. The prototype adjustable light source is capable of maintaining an average color rendering index greater than 92 (nearly the quality of daylight) across a broad adjustable range (2800 K - 10,000 K) and offers two modes of control, one of which is an energy efficient mode that reduces the total power consumption by 20%. The lighting network is capable of measuring the illuminance and color temperature at a surface and adjusting its output with an overall update rate of 11 Hz (limited by the MATLAB kernel). The sensor node features an optical suite of sensors with a dynamic range of 10000 : 1 lx (rms error: 2 lx). The sensor node measures the color temperature of daylight within ±500 K (kelvin). Device testing and validation were performed in a series of experiments in which the radiant power was collected using a radiometrically calibrated spectrometer with an expanded uncertainty (k = 2) of 14% and validated against a model derived by measuring the individual spectra of the system using custom MATLAB tools. A digital multimeter measured the current in the experiments. The work concludes by estimating the energy savings based on the measured optical and electrical data. In environments with moderate ambient lighting, the networked control reduces power consumption by 44% with an additional 5-10% possible with spectral optimization.
by Matthew Aldrich.
S.M.

Doutoramento em Física
The presente work aims to synthesize new bridge silsesquioxanes organic-inorganic hybrid materials, and characterize the local structure and photoluminescence properties overlooking potential applications in the area of green photonics, namely, in solid-state lighting and luminescent solar concentrators. In this context, three distinct families of materials based on six precursors which differ in their structural organization were synthesized, i.e. precursors with structure: 1) linear where the organic component is based on malonamide group, P2-m and P4-m; 2) linear which has been added an aromatic ring whose organic part is based on amide and/or thioamida, P(UU), P(UT) and P(TT) and 3) branched which the organic component is based on amide group, t-UPTES (5000). Two organic-inorganic hybrids (M2-m e M4-m) which results from hydrolysis and condensation of the precursors P2-m e P4-m were synthetized. The role of the presence of one or two malonamide groups was studied in terms of local structure and photoluminescence properties. Three organic-inorganic hybrids H(UU), H(UT) and H(TT) based on P(UU), P(UT) and P(TT) were synthesized and structurally characterized aiming to study the role of the hydrogen bond in the self-assembling of these materials. The presence of different types of hydrogen bonds (bifurcated, linear and cyclic) induces different conformations which affect the physical properties (mechanical and optical) of the materials. Hybrids based on t-UPTES(5000) precursor were synthesized based on different synthesis strategies. Changing the concentration of HCl and water content as well as the synthesis in a controlled environment allowed the improvement of the optical properties of this system, in particular, the absolute emission quantum yield and the absorption coefficient. In addition, it were studied the recombination mechanisms responsible for the emission through the comparison between the corresponding photoluminescence properties of the organic and inorganic models. Finally, due to the structural simplicity of the precursors P2-m and P4-m, these were doped with Eu3+. The local structure of the corresponding hybrids shows local coordination between the ion and the host. Efficient materials concerning the absolute emission quantum yield values motivated the development of luminescent solar concentrators with a maximum absolute emission quantum yield of 0.600.06 and optical conversion efficiency in the absorption spectral region (300-380 nm) of 12.3%.
O presente trabalho propõe sintetizar novos materiais híbridos orgânicos-inorgânicos do tipo silsesquioxanos em ponte e caracterizar a sua estrutura e propriedades de fotoluminescência com vista a potenciais aplicações na área da fotónica sustentável, nomeadamente, iluminação de estado sólido e concentradores solares luminescentes. Neste âmbito, foram sintetizadas três famílias distintas de materiais baseados em seis precursores que diferem na sua organização estrutural, ou seja, precursores com estrutura: 1) linear onde a componente orgânica é baseada no grupo malonamida, P2-m e P4-m; 2) linear onde foi adicionado um anel aromático cuja componente orgânica é baseada em amida e/ou thioamida, P(UU), P(UT) e P(TT), e 3) tri-ramificada onde a componente orgânica é baseada no grupo amida, t-UPTES(5000). Dois híbridos orgânicos-inorgânicos (M2-m e M4-m) que resultam da hidrólise e condensação dos precursores P2-m e P4-m foram sintetizados. O papel da presença de um ou dois grupos malonamida foi estudado em termos de estrutura local e propriedades de fotoluminescência. Três híbridos orgânicos-inorganicos, H(UU), H(UT) e H(TT), baseados, respetivamente, em P(UU), P(UT) e P(TT), foram sintetizados e caracterizados estruturalmente com o objetivo de estudar o papel das ligações de hidrogénio na auto-organização destes materiais. A presença de diferentes tipos de ligações de hidrogénio (bifurcada, linear e cíclica) induz diferentes tipos de configurações que têm influência nas propriedades físicas (mecânicas e óticas) dos materiais. Híbridos baseados no precursor t-UPTES(5000) foram sintetizados tendo em conta diferentes estratégias de síntese. A variação da concentração de HCl e quantidade de água bem como a síntese em ambiente controlado permitiram melhorar as propriedades óticas deste sistema nomeadamente, o rendimento quântico absoluto e o coeficiente de absorção. Foram também discutidos, os mecanismos de recombinação responsáveis pela emissão através da comparação das propriedades de fotoluminescência observadas nos correspondentes modelos orgânicos e inorgânicos. Finalmente, devido à simplicidade estrutural os precursores P2-m e P4-m, estes foram dopados com Eu3+. A estrutura local dos correspondentes híbridos mostra coordenação local entre o ião e a matriz. Materiais eficientes do ponto de vista de rendimento quântico absoluto motivaram o desenvolvimento de concentradores solares luminescentes que apresentam rendimento quântico absoluto máximo de 0.600.06 e eficiência ótica de conversão na região espetral de absorção (300-380 nm) de 12.3 %.

Phases organiques luminescentes qui sont incorporés dans une matrice inorganique conductrice est proposé dans cette étude pour la couche active d'une diode émettant de la lumière hybride. Dans ce composite, le colorant organique joue le rôle de site de recombinaison radiative de porteurs de charge qui sont injectées dans la matrice de transport ambipolaire inorganique. Comme l'un des combinaisons de matériaux de candidat, bicouche et des films minces composites de ZnSe et un complexe d'iridium rouge (Ir(BPA)) émetteur de lumière organique ont été préparé in situ par UHV technique d'évaporation thermique. Les alignements de bande d'énergie mesurée par spectroscopie de photoélectrons (PES) pour le ZnSe/Ir(BPA)et deux couches de ZnSe+Ir(BPA) révèlent que le composite HOMO et LUMO du colorant organique sont positionnées dans la largeur de bande interdite de ZnSe. Cette gamme offre les forces motrices énergiques nécessaires pour les transferts d'électrons et de trous de ZnSe à Ir(BPA). Par l'interprétation des données du PES,la composition chimique des interfaces ont également été déterminés. Le ZnSe/Ir(BPA) interface est réactive, même si elle est d'une pureté de matériaux de haute.Pendant ce temps, l'Ir (BPA)/ZnSe interface ne présente pas la pureté matériel. Ceci est représenté à la nature de ZnSe évaporation comme Zn particuliers et des fluxSE2, associée à des interactions chimiques avec le Ir(BPA) substrat. L'interface est,de ce fait, composé d'une multitude de phases, les phases de Se0, ZnSe rares, réduit Se et oxydé molécules de colorant, et de Zn qui sont intercalées atomes dans leIr(BPA) substrat. PES des composites ZnSe+Ir(BPA) révèle des tendances similaires à l'Ir(BPA)/ZnSe interface. A des émissions de lumière rouge surfaciques et intermittents fanées ont été observés à partir de dispositifs qui incorporent couches alternées séquences de ZnSe et Ir(BPA) pour la couche active
Luminescent organic phases that are embedded in a conductive inorganicmatrix is proposed in this study for the active layer of a hybrid light-emitting diode. Inthis composite, the organic dye acts as the radiative recombination site for chargecarriers that are injected into the inorganic ambipolar transporting matrix. As one ofthe candidate material combinations, bilayer and composite thin films of ZnSe and ared iridium complex (Ir(BPA)) organic light emitter were prepared in situ via UHVthermal evaporation technique. The energy band alignments measured byphotoelectron spectroscopy (PES) for the ZnSe/Ir(BPA) bilayer and ZnSe+Ir(BPA)composite reveal that the HOMO and LUMO of the organic dye are positioned in theZnSe bandgap. This lineup provides the required energetic driving forces for electronand hole transfers from ZnSe to Ir(BPA). By interpreting PES data, the chemicalcomposition of the interfaces were also determined. The ZnSe/Ir(BPA) interface isreactive even though it is of high material purity. Meanwhile, the Ir(BPA)/ZnSeinterface does not exhibit material purity. This is accounted to the nature of ZnSeevaporation as individual Zn and Se2 fluxes, coupled with chemical interactions withthe Ir(BPA) substrate. The interface is, thereby, composed of an abundance of Se0phases, sparse ZnSe phases, reduced Se and oxidized dye molecules, and Znatoms that are intercalated into the Ir(BPA) substrate. PES of the ZnSe+Ir(BPA)composites reveals similar trends to the Ir(BPA)/ZnSe interface. A faded areal andintermittent red light emissions were observed from devices that incorporatedalternating layer sequences of ZnSe and Ir(BPA) for the active layer

Solid state white light emitting diode lighting devices outperform conventional light sources in terms of lifetime, durability, and lumens per watt. However, the capital contribution is still to high to encourage widespread adoption. Furthermore, the colour from today's devices is unsuitable for general room illumination and thus new phosphor materials are needed. This dissertation will examine the synthesis of inorganic nanoparticles and the possibility of using hybrid inorganic-organic frameworks in the search for new lighting phosphors. Nanoparticles of the oxide compound yttrium aluminium garnet were synthesized using an emulsion technique, though it was found that the high temperature processing needed for good optical properties was not compatible with maintaining nanosized particles. In terms of hybrid framework phosphors, several aspects of this new area have been explored. The mechanical and optical properties of a dense cerium oxalate formate hybrid framework compound have been investigated. Its strength was found to be nearly as great as some classical ceramic compounds, and clearly robust enough for device applications. While the photoluminescence of the cerium oxalate formate was not suitable for solid state lighting, the impressive mechanical properties evaluated are expected to be valid for a wide range of dense inorganic-organic frameworks. A novel approach to solid state lighting phosphors was introduced by using ligand-based photoluminescence in hybrid frameworks. Novel frameworks were prepared using 9,10-anthraquinone-2,3-dicarboxylic acid in combination with calcium, manganese, nickel, and zinc. These compounds show excellent photoluminescent emission for use in solid state lighting applications, although the luminescence is quenched at room temperature due to dynamic effects. The excitation, while reaching the blue part of the spectrum, falls just short of what is needed for use today's devices. To address these issues, a second class of novel framework compounds was prepared using 9-fluorenone-2,7-dicarboxylic acid in combination with calcium, strontium, barium, cadmium, and manganese. They are more rigid structures and show good luminescence at room temperature with a photoluminescent excitation spectrum extending further into the blue than the anthraquinones. Additionally, quantum yield in the calcium fluorenone is nearly double that of its parent ligand, suggesting that there is an enhancement in luminescent properties as a result its inclusion in a framework structure. An explanation for the differences in efficiency between seemingly similar compounds are drawn from their compositions, crystal structures, photoluminescence, and specific heat properties. Finally, some structural and chemical targets for future hybrid phosphor development are identified based on the relationships identified in this work.

Mestrado em Engenharia Física
Nos anos recentes a iluminação de estado sólido impulsionou alternativas de iluminação efí cientes e ecológicas. Os desafi os correntes envolvem o desenvolvimento de materiais emissores de luz que convertem radiação de uma determinada energia para radiação de energia mais baixa, na gama do visível. Esta tese estuda um complexo novo, Tb(NaI)3(H2O)2 onde NaI é o ácido nalidíxico, que emite na região do verde e é estável sob iluminação no ultravioleta. Este foi incorporado em materiais híbridos orgânico-inorgânico tripodais com dois pesos moleculares médios (3000 e 5000 g.mol-1, denominados t- U(3000) e t-U(5000) respetivamente) que permitem o processamento de monólitos e fi lmes com forma e espessura controlada. Estes híbridos também aumentam o rendimento quântico absoluto de emissão de 0.11 medidos para o Tb(NaI)3(H2O)2 isolado para ~0.82 após incorporação no t-U(5000). Foi também demonstrado o potencial de usar estes materiais híbridos como emissores na região verde para uso em iluminação de estado sólido através do revestimento do díodo emissor na região ultravioleta (365 nm). Este LED apresenta uma efi cácia de 1.3 lm.W􀀀1.
In the last few years, solid state light-emitting diodes (LEDs) have been driving the lighting industry towards energy e cient and environmental friendly lighting. Current challenges encompass e cient and low-cost downconverting photoluminescent phosphors with emission in the visible region. This thesis will cover a novel UV-photostable green emitting complex, Tb(NaI)3(H2O)2 where NaI is nalidixic acid, was incorporated into organic-inorganic tripodal hybrid materials with two average molecular weights (3000 and 5000 g.mol{1, termed as t- U(5000) and t-U(3000), respectively) which enable the easy shaping of monoliths and lms with controlled thickness. Moreover, the hybrid hosts boost the Tb3+ green absolute emission quantum yield from 0.11 measured for the isolated Tb(NaI)3(H2O)2 complex to 0.82 after incorporation into t-U(5000). The potential use of the hybrid materials as UV-down converting green-emitting phosphors for solid state lighting was demonstrated by means of coating a near-UV LED (365 nm). This LED shows an e cacy of 1.3 lm.W􀀀1.

Thesis (S.M.M.O.T.)--Massachusetts Institute of Technology, Sloan School of Management, Management of Technology Program, 2004.
Includes bibliographical references (p. 98-102).
Combining an understanding of the technical progress and potential of semiconductor light emitting materials with an analysis of market adoption reveals useful insights into challenges and opportunities in the growing field of solid state lighting. The integration of discrete LEDs into solid state lighting systems is identified as a critical area of both technical and business development and the key to creating useful products and expanding new markets. Analysis of conventional and emerging optosemiconductor lighting industries highlights important differences of influence within the value chain. For solid state lighting, the significance of system integration shifts control away from large LED manufacturers and closer to the end user. Special focus on companies pursuing the system integrator role compares strategies for technology based niche players with strategies for joint venture companies formed by alliances of large lighting and semiconductor companies. Based on technology capability, industry conditions, and historical analogy, solid state lighting is projected to achieve wider adoption primarily through the growth of new applications and markets, not through the substitution of existing lighting business.
by Timothy L. Kelly.
S.M.M.O.T.

This thesis presents the results of an experimental study dealing with conservation of artefacts and visual perception for visitors when Solid State Lighting (SSL) is used in museums. The characterization of white LED sources with different spectral distribution has been carried out, focussing on colour rendering properties and potential damage for museum collections. Conservative aspects have been further investigated with experimental series on fading of light-responsivity materials, showing the suitability of LEDs with respect to traditional light sources such as dichroic halogen lamps. The study on visual comfort and perception of artworks under SSL has been conducted through objective and subjective evaluations of different LED system configurations within a typical museum showcase. The results have demonstrated the potential suitability of LED lighting for this application, but also outlined some drawbacks with respect to lighting quality and visibility of displayed objects.

The role of high-power white LEDs in general lighting applications is becoming, day-by-day, increasingly important. The reliability of these devices, compared to that of conventional light sources, represents one of the keys for their development and their market penetration. It is then of fundamental importance to deeply understand the various degradation mechanisms that affect the operation of LEDs, in terms of lifetime, chromaticity characteristics and efficiency. This thesis reports the results of a research activity focused on several issues related to the reliability of LED-based lighting systems. After an initial overview on the most important theoretical concepts necessary for the understanding of the physical results, three main sections can be identified in this thesis, concerning the presentation of research activity: • The first section reports an extensive study on one of the most critical Electrical Over Stress (EOS) phenomena, called “Hot-plugging”, which occurs when an LED module is directly connected to an energized power supply and can generate current spikes up to several tens of amperes that can potentially destroy or damage the LEDs. The aim of this section is to analyze, for the first time, the nature of the current spikes generated during hot-plugging and to present a simplified model to explain the hot plugging phenomenon. The study is based on transient electrical measurements, carried out on several LED modules (fabricated by different manufacturers), connected to three different power supplies. Results reveal that the amplitude and the time constants of the current spikes are directly determined by the number of LEDs connected in series and by the output capacitance of the current driver. • Afterwards, the second section presents an extensive study on the effects of Electrostatic Discharges (ESD) on state-of-the-art GaN based LEDs, based on optical and electrical measurements carried out during the ESD events. ESD events were simulated through a Transmission Line Pulser (TLP), which generates voltage pulses with a duration of 100ns and increasing amplitude: during each pulse, spatially resolved electroluminescence measurements were carried out through a high speed EMCCD camera. These measurements allowed to identify the chip region where the discharge is localized and the change in the damaged area induced by consecutive ESD events. In addition, the current and voltage waveforms at the LED terminal were monitored during the tests; this analysis provided important information about modifications the impedance of the devices. The analysis was carried out on different types of commercially available low-power GaN-based LEDs with several differences in the manufacturing technology. Thanks to these tests, we have identified two different failure behaviors during a destructive ESD event, clearly related to the different defects in the semiconductor lattice and to structure of the chip. • The last section investigates the thermal stability of remote phosphor plates to be used in solid-state lighting systems, for the conversion of the blue light emitted by GaN-based LEDs into white light. A preliminary thermal characterization revealed that in normal conditions of blue light irradiance the phosphor plates could reach temperature levels higher than 60°C, which can affect both performance and reliability. The results of accelerated thermal stress tests indicate that high temperature levels can trigger a relevant degradation mechanism (estimated activation energy is 1.2 eV), that drastically reduces the phosphor conversion efficiency and modifies the photometric and colorimetric characteristics of the emitted white light.
Il ruolo dei LED bianchi di potenza sta diventando, giorno dopo giorno, sempre più importante. L’affidabilità di questi dispositivi, paragonata a quella delle sorgenti di luce tradizionali, rappresenta uno dei fattori chiave per il loro sviluppo e la loro penetrazione nel mercato. E’ quindi di fondamentale importanza conoscere in modo approfondito i diversi meccanismi di degrado che possono influenzarne il funzionamento in termini di tempo di vita, caratteristiche cromatiche ed efficienza. Questa tesi riporta i risultati di un’attività di ricerca incentrata su alcune problematiche relative all’affidabilità di sistemi illuminazione allo stato solido. Dopo una panoramica iniziale sui concetti teorici necessari per comprendere appieno i risultati, in questa tesi possono essere indentificate tre diverse sezioni che presentano l’attività di ricerca del dottorato: • la prima parte riporta uno studio estensivo su uno dei più critici fenomeni di Electrical Over Stress (EOS), chiamato “Hot-Plugging”, che accade quando un modulo LED è direttamente connesso ad un driver LED precedentemente alimentato e può generare picchi di corrente fino ad alcune decine di ampere, che possono potenzialmente distruggere o danneggiare i LED. Lo scopo di questa sezione è analizzare, per la prima volta, la natura dei picchi di corrente generati durante l’“hot-plugging” e proporre un modello semplificato per spiegare il fenomeno. Lo studio è basato sulla misura dei transienti elettrici, svolta su diversi moduli LED (scelti tra diversi produttori), connessi a tre diversi tipi di alimentatori. I risultati rivelano che l’ampiezza e le costanti di tempo dei picchi di corrente sono direttamente determinate dal numero di LED connessi in serie e dalla capacità di uscita dell’alimentatori; • la seconda parte presenta un completo studio sugli effetti delle scariche elettrostatiche (ESD) su LED al Nitruro di Gallio (GaN), basato su misure elettriche e ottiche svolte durante l’evento ESD. Le scariche elettrostatiche sono state simulate tramite un Transmission Line Pulser (TLP) che genera impulsi di tensione con una durata di 100 ns e ampiezza crescente: durante ciascun impulso sono state svolte misure di elettroluminescenza grazie ad una camera EMCCD (Electon Multiplying Charge Coupled Device) ad alta velocità. Queste misure permettono di identificare la regione del chip dove la scarica è localizzata e i cambiamenti nell’area danneggiata indotti da eventi ESD consecutivi. Inoltre, le forme d’onda di corrente e tensione ai terminali del LED sono state monitorate durante i test; tale analisi fornisce importanti informazioni circa le modifiche di impedenza dei dispositivi. L’analisi è stata svolta su diversi tipi di LED commerciali a media potenza con alcune differenze nelle tecnologie di fabbricazione. Grazie a questi test sono stati indentificati due differenti comportamenti di failure durante eventi ESD distruttivi, chiaramente correlati ai diversi difetti nel cristallo del semiconduttore e alla struttura del chip; • l’ultima sezione riporta uno studio sulla stabilità termica di piastre di “fosfori remoti” usate in sistemi di illuminazione allo stato solido per convertire la luce blu generata dai LED in luce bianca. Una caratterizzazione termica preliminare rivela che, in normali condizioni operative sotto illuminazione a luce blu, la piastra di fosfori può raggiungere temperature fino a 60°C, che possono influenzarne sia le performance che l’affidabilità. I risultati di stress termici accelerati indica che alti livelli di temperatura possono condurre ad un rilevante meccanismo di degrado (l’energia di attivazione stimata è 1.2 eV), che riduce drasticamente l’efficienza di conversione fosforosa e modifica le caratteristiche fotometriche e colorimetriche della luce bianca emessa.

Business Administration/Strategic Management
Ph.D.
My dissertation is a study of firms’ strategic differences and the performance consequences of these differences in nascent industries. I relax the implicit assumption in the existing literature that a technological breakthrough is exogenous, and provide theoretical and empirical accounts of knowledge evolution before a new technology gets commercialized. In Chapter 2, I highlight the evolution of a technology at the industry level and argue that there exists a pre-commercialization technology life cycle. I develop a series of propositions related to the technology’s architectural evolution during the pre-commercialization phase, and show that an emerging architecture becomes fully integrated before the inception of a new market. In Chapter 3, I shift the focus to the firm level, and compare the pre-commercialization search strategies of market incumbents facing a technological obsolescence to those of technology incumbents disrupting an existing market. I show that these two groups of incumbent firms invest heavily in an emerging technology even before the market takes shape, and that they engage in different search strategies, specifically in the degree to which they integrate or modularize the knowledge about individual technology components across two stages of a pre-commercialization life cycle. In Chapter 4, I argue that such pre-commercialization strategies have post-commercialization consequences. This dynamic view suggests that a select group of established organizations enter a new product market and the heterogeneity in their pre-entry experiences has direct consequences for the product’s initial performance. Throughout, this study uses the emergence of the solid-state lighting (SSL) market as an empirical context.
Temple University--Theses

Metal/organic/indium tin oxide (ITO) structures, including OLEDs, are demonstrated to contain multiple nonvolatile conductance states that can be programmed by the application of an external bias above a certain threshold voltage (Vth). These conductance states are stable and in turn can be probed by the use of a bias lower in value than Vth. The unbiased retention time of states is greater than several weeks, and more than 48,000 write-read-rewrite-read cycles have been performed with minimal degradation. It is found that the programming of a continuum of conductance states is possible, and techniques to do so are outlined. The electrical conductivity of the highest and lowest states can differ by six orders of magnitude. Switching speeds below 50 ns are shown, resulting in an energy requirement of about 100 pJ to switch from one conductance state to another. The memory phenomenon is shown to be influenced by the active layer thickness and anode/surface roughness while temperature dependence is limited. The electrical characteristics of these devices are consistent with metal diffusion or filament phenomena found in metal-insulator-metal structures, suggesting a possible mechanism by which the states are stored.Electroluminescent devices employing several new organic-inorganic lumophore-functionalized macromolecules are presented. In this study, macromolecules incorporating several lumophores covalently bonded to the vertices of a cubical core structure based on Polyhedral Oligomeric Silsesquioxane (POSS) in multiple configurations are implemented as light-emitting centers. The hole-transporting polymer poly(N-vinylcarbazole) (PVK) and electron-transporting additive 2-(4-biphenylyl)-5-(4-tert-butylphenyl)1,3,4-oxadiazole (PBD) are used as a two-part host to enhance the carrier transport in these simple solution-processed single-layer devices. A study of energy transfer in several systems is carried out to understand the requirements needed to create white-light emission from a single macromolecule. A single macromolecule incorporating twenty-one blue and one yellow lumophore is shown to exhibit field-independent stable white-light electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.31, 0.37). An external quantum efficiency of 0.55 percent and a maximum brightness of 1600 cd/m2 are attained with simple solution-processed single-layer devices. High solubility and ease of purification give these macromolecule white-light emitters advantages over their small molecule and polymeric type counterparts.

In recent years, high brightness light emitting diodes (HBLEDs) have increasingly attracted the interest of both industrial manufacturers and academic research community. Among the several aspects that make LED technology so attractive, the most appreciated characteristics are related to their robustness, high efficiency, small size, easy dimming capability, long lifetime, very short switch-on/switch-off times and mercury free manufacturing. Even if all such qualities would seem to give to solid state lighting a clear advantage over all the other kinds of competing technologies, the issues deriving from the need of LED technology improvement, on one hand, and of the development of suitable electronic ballasts to properly drive such solid state light sources, on the other, have so far hindered the expected practical applications. The latter problem, in particular, is nowadays considered the main bottleneck in view of a widespread diffusion of solid state technology in the general lighting market, as a suitable replacement of the still dominant solutions, namely halogen and fluorescent lamps. In fact, if it is true that some aspects of the devices’ technology (e.g. temperature dependent performance, light quality, efficiency droop, high price per lumen, etc…) still need further improvements, it is now generally recognized that one of the key requirements, for a large scale spread of solid state lighting, is the optimization of the driver. In particular, the most important specifications for a LED lamp ballast are: high reliability and efficiency, high power factor, output current regulation, dimming capability, low cost and volume minimization (especially in domestic general lighting applications). From this standpoint, the main goal is, therefore, to find out simple switched mode power converter topologies, characterized by reduced component count and low current/voltage stresses, that avoid the use of short lifetime devices like electrolytic capacitors. Moreover, if compactness is a major issue, also soft switching capability becomes mandatory, in order to enable volume minimization of the reactive components by increasing the switching frequency in the range of the hundreds of kHz without significantly affecting converter’s efficiency. It is worth mentioning that, in order to optimize HBLED operation, also other matters, like the lamp thermal management concern, should be properly addressed in order to minimize the stress suffered by the light emitting devices and, consequently, the deterioration of the light quality and of the expected lamp lifetime. However, being this work focused on the issues related to the research of innovative driving solutions, the aforementioned thermal management problems, as also all the topics related to the improvement of solid state devices’ technology, will be left aside. The main goal of the work presented in this thesis is, indeed, to find out, analyze and optimize new suitable topologies, capable of matching the previously described specifications and also of successfully facing the many challenges dictated by the future of general lighting. First of all, a general overview of solid state lighting features, of the state of the art of lighting market and of the main LED driving issues will be provided. After this first introduction, the offline driving concern will be extensively discussed and different ways of approaching the problem, depending on the specific application considered, will be described. The first kind of approach investigated is based on the use of a simple structure relying on a single power conversion stage, capable of concurrently ensuring: compliance with the standards limiting the input current harmonics, regulation of the load current and also galvanic isolation. The constraints deriving from the need to fulfil the EN 61000-3-2 harmonics standard requirements, when using such kind of solution for low power (<15W) LED driving purposes, will be extensively discussed. A low cost, low component count, high switching frequency converter, based on the asymmetrical half bridge flyback topology, has been studied, developed and optimized. The simplicity and high compactness, characterizing this solution, make it a very good option for CFL and bulb replacement applications, in which volume minimization is mandatory in order to reach the goal of placing the whole driving circuitry in the standard E27 sockets. The analysis performed will be presented, together with the design procedure, the simulation outcomes and the different control and optimization techniques that were studied, implemented and tested on the converter's laboratory prototype. Another interesting approach, that will be considered, is based on the use of integrated topologies in which two different power conversion stages are merged by sharing the same power switch and control circuitry. In the resulting converter, power factor correction and LED current regulation are thus performed by two combined semi-stages in which both the input power and the output current have to be managed by the same shared switch. Compared with a conventional two-stages configuration, lower circuit complexity and cost, reduced component count and higher compactness can be achieved through integration, at cost of increased stress levels on the power switch and of losing a degree of freedom in converter design. Galvanic isolation can be provided or not depending on the topologies selected for integration. If non-isolated topologies are considered for both semi-stages, the user safety has to be guaranteed by assuring mechanical isolation throughout the LED lamp case. The issue, deriving from the need of smoothing the pulsating power absorbed from the line while avoiding the use of short lifetime electrolytic capacitors, will be addressed. A set of integrated topologies, used as HBLED lamp power supplies, will be investigated and a generalized analysis will be presented. Their input line voltage ripple attenuation capability will be examined and a general design procedure will be described. Moreover, a novel integrated solution, based on the use of a double buck converter, for an about 15W rated down-lighting application will be presented. The analysis performed, together with converter design and power factor correction concerns will be carefully discussed and the main outcomes of the tests performed at simulation level will be provided. The last kind of approach to be discussed is based on a multi-stage structure that results to be a suitable option for medium power applications, like street lighting, in which compactness is not a major concern. By adopting such kind of solution it is, indeed, possible to optimize converter’s behavior both on line and on load side, thereby guaranteeing both an effective power factor correction at the input and proper current regulation and dimming capability at the output. Galvanic isolation can be provided either by the input or the output stage, resulting in a standard two stage configuration, or by an additional intermediate isolated DC-DC stage (operating in open loop with a constant input/output voltage conversion ratio) that namely turns the AC/DC converter topology into a three stage configuration. The efficiency issue, deriving from the need of multiple energy processing along the path between the utility grid and the LED load, can be effectively addressed thanks to the high flexibility guaranteed by this structure that, relaxing the design constraint, allows to easily optimize each stage. A 150W nominal power rated ballast for street solid state lighting applications, based on the latter (three stage) topology, has been investigated. The analysis performed, the design procedure and the simulations outcomes will be carefully described, as well as the experimental results of the tests made on the implemented laboratory prototype.
Negli ultimi anni i dispositivi LED di potenza ad elevata luminosità (HBLED) hanno attirato in misura sempre crescente l'interesse della comunità scientifica, sia all'interno del mondo accademico che di quello industriale. Tra le varie caratteristiche, che rendono questo tipo di tecnologia interessante, le qualità più apprezzate sono certamente: la robustezza, l'elevata efficienza, le piccole dimensioni, la facilità di modulazione dell'intensità luminosa, il lungo tempo di vita, l'estrema rapidità di accensione e spegnimento e l'assenza di mercurio. Nonostante tutti questi aspetti sembrino dare alla tecnologia a stato solido un netto vantaggio rispetto alle tecnologie concorrenti, l'utilizzo dei LED di potenza nel campo dell'illuminazione rimane a tutt'oggi abbastanza limitato. La necessità di ulteriori progressi nella tecnologia dei dispositivi, da un lato, e dello sviluppo di soluzioni in grado di garantirne il corretto ed efficiente pilotaggio, dall'altro, ne hanno, infatti, fino ad ora frenato la diffusione rispetto alle attese. Quest'ultimo aspetto, in particolare, è al giorno d'oggi considerata il vero "collo di bottiglia" in vista dell'impiego su larga scala della tecnologia a stato solido, in sostituzione delle soluzioni, tutt'ora dominanti nel mercato dell'illuminazione, basate sull'utilizzo di lampade alogene e a fluorescenza. Se, da un lato, infatti, è vero che alcuni aspetti della tecnologia dei dispositivi (e.g. variabilità delle prestazioni con la temperatura, qualità della luce, calo dell'efficienza luminosa con l'aumentare della corrente, elevato costo per lumen, ecc...) necessitano di essere ulteriormente perfezionati, dall'altro è ormai universalmente riconosciuto che l'elemento chiave per l'ampia diffusione dell'illuminazione a stato solido è proprio l'ottimizzazione dello stadio di alimentazione. In particolare, le specifiche più importati che un ballast per lampade a LED è tenuto a soddisfare sono: elevata affidabilità ed efficienza, elevato fattore di potenza, capacità di regolazione della corrente di uscita e di modulazione del flusso luminoso, basso costo e minimo ingombro (soprattutto nell'illuminazione domestica). L'obiettivo principale è, quindi, riuscire ad ideare soluzioni basate sull'utilizzo di topologie semplici, caratterizzate da ridotto numero di componenti e limitati livelli di stress di corrente e tensione, che non prevedano l'impiego di componenti con breve tempo di vita come i condensatori elettrolitici. Inoltre, nelle applicazioni in cui la compattezza è considerata uno degli aspetti di maggior rilievo, anche la capacità di operare in soft-switching diviene una specifica indispensabile. Ciò è infatti necessario al fine di permettere la minimizzazione del volume delle componenti reattive, tramite l'aumento della frequenza di commutazione nel range delle centinaia di kHz, senza compromettere l'efficienza del convertitore. Per completezza, vale la pena di ricordare che, per ottimizzare il funzionamento dei LED ad elevata luminosità, andrebbero presi in considerazione anche altri aspetti, come ad esempio le problematiche legate alla gestione del calore dissipato dalla lampada, importanti al fine di limitare gli stress termici subiti dai dispositivi e, di conseguenza, migliorare la qualità della luce emessa e massimizzare il tempo di vita della lampada. Tuttavia, essendo il lavoro presentato in questa tesi centrato sulle questioni relative allo stadio di alimentazione, i suddetti problemi di gestione termica, come anche gli aspetti relativi allo sviluppo della tecnologia dei dispositivi non verranno esaminati. L'obiettivo principale del lavoro che verrà descritto nel corso dei prossimi capitoli, è, infatti, la ricerca di soluzioni innovative per il pilotaggio da rete elettrica di lampade basate su tecnologia a stato solido. Verranno pertanto approfonditamente trattate le tematiche relative ad analisi, ottimizzazione e sviluppo di topologie che siano in grado di soddisfare i requisiti precedentemente enunciati e di affrontare con successo le sfide proposte dalla continua evoluzione dello scenario del "general lighting". Per prima cosa, sarà fornita una visione di insieme riguardante lo stato dell'arte del mercato dell'illuminazione, le caratteristiche dei dispositivi di illuminazione a stato solido ed i principali aspetti relativi al loro pilotaggio. Dopo questa prima sezione introduttiva, la tematica relativa all'alimentazione da rete elettrica di tali dispositivi verrà approfonditamente discussa. Differenti modi di approcciare il problema, a seconda della specifica applicazione considerata, verranno discussi. Il primo tipo di approccio che verrà esaminato si basa sull'uso di una semplice struttura, formata da un singolo stadio di conversione di potenza. Essa è in grado di fornire al contempo il rispetto degli standard che limitano il contenuto armonico della corrente di ingresso, l'isolamento galvanico e la regolazione della corrente e dell'intensità luminosa in uscita. I vincoli, dettati dall'esigenza di garantire il rispetto della normativa EN 61000-3-2, in applicazioni di bassa potenza (<15W) prive di uno stadio dedicato alla correzione del fattore di potenza, verranno approfonditamente trattati. Saranno, poi, illustrati i risultati dello studio, sviluppo ed ottimizzazione di un convertitore a singolo stadio, operante ad elevata frequenza di commutazione, basato sulla topologia flyback a mezzo ponte asimmetrico. La semplicità, il ridotto numero di componenti ed il basso costo, che caratterizzano tale tipo di soluzione, la rendono adatta all'alimentazione di lampade per il settore residenziale, in cui la compattezza dello stadio di alimentazione è di fondamentale importanza al fine di consentirne l'alloggiamento nei classici socket E27. L'analisi effettuata, la procedura di progetto ed risultati ottenuti in simulazione ed a livello sperimentale durante lo studio di tale topologia verranno accuratamente descritti e discussi. Un altro interessante tipo di approccio che verrà considerato si basa sull'utilizzo di topologie integrate, nelle quali due diversi stadi di conversione vengono uniti tramite la condivisione dello stesso interruttore di potenza e della relativa circuiteria di comando. Nel convertitore che ne risulta, la correzione del fattore di potenza e la regolazione della corrente nei LED saranno dunque garantite dalla combinazione dei due semi-stadi, il cui interruttore comune dovrà essere in grado di gestire sia la potenza di ingresso che la corrente di uscita. Rispetto alla configurazione a due stadi convenzionale, la soluzione ottenuta tramite l'integrazione consente una minore complessità circuitale, un ridotto numero di componenti e, di conseguenza, una maggiore compattezza ed un minor costo. Tutto ciò viene guadagnato a scapito di un maggiore livello di stress nei componenti e della perdita di un grado di libertà nel progetto del convertitore. L'isolamento galvanico può essere garantito o meno a seconda del tipo di topologie che vengono selezionate per l'integrazione. Se la scelta ricade su topologie non isolate, la sicurezza dell'utente andrà comunque garantita isolando meccanicamente l'involucro della lampada. I problemi legati alla necessità di smorzare la componente alternata della potenza assorbita dalla rete, evitando al contempo l'utilizzo di componenti con basso tempo di vita, come i condensatori elettrolitici, verranno discussi. A tal proposito si studieranno le caratteristiche di un insieme di topologie integrate, al fine di fornirne un'analisi ed una procedura di design generalizzate. Se ne esaminerà, inoltre, la capacità di attenuare la componente ondulatoria della tensione di ingresso che viene trasferita al carico, dove si traduce in un'oscillazione della corrente di alimentazione fornita ai LED. Verrà proposta, poi, una soluzione basata su una topologia derivante dall'integrazione di due convertitori di tipo step-down (abbassatori di tensione), per applicazioni di "down-lighting", dimensionata per una potenza di circa 15W. Se ne discuteranno, in particolare, i dettagli di maggiore interesse relativi all'analisi effettuata, alla procedura di progetto ed ai risultati dei test effettuati in ambiente di simulazione. L'ultimo tipo di approccio considerato prevede, infine, l'utilizzo di una topologia multi-stadio, ritenuta una scelta appropriata soprattutto per applicazioni lighting di potenza elevata (>60W), come l'illuminazione stradale, in cui la compattezza dell'alimentatore non è ritenuta un aspetto di primaria importanza. Tramite questo tipo di soluzione è, infatti, possibile ottimizzare le prestazioni del convertitore sia dal lato della rete che dal lato del carico. Si riescono a garantire, in tal modo, un'efficace correzione del fattore di potenza, un adeguato controllo della corrente di uscita ed un'appropriata modulazione del flusso luminoso emesso dalla lampada. L'isolamento galvanico può essere fornito dallo stadio di ingresso o da quello di uscita o da un aggiuntivo stadio DC-DC intermedio, operante a catena aperta con rapporto di conversione di tensione costante. In quest'ultimo caso la struttura del convertitore, si trasforma, dalla classica configurazione a due stadi, in una topologia a triplo stadio. Il problema che nasce dalla necessità di assicurare un elevato livello di efficienza del sistema, nonostante l'interposizione di ripetuti stadi di conversione dell'energia tra la rete ed il carico a LED, può essere efficacemente risolto grazie alla flessibilità che caratterizza tale tipo di struttura. L'aumento del numero dei gradi di libertà in fase progettuale permette, infatti, di ottimizzare con semplicità ogni singolo stadio. Per comprovare limiti e potenzialità di tale tipo di approccio, si è deciso di studiare un ballast (dimensionato per una potenza nominale di 150W) basato sulla topologia a triplo stadio precedentemente menzionata, per applicazioni nell'ambito dell'illuminazione stradale. L'analisi condotta, la procedura di progetto ed i risultati delle simulazioni effettuate verranno discussi nel dettaglio, così come i risultati sperimentali dei test di laboratorio effettuati sul prototipo costruito.

Thesis (Master of Business Administration)--Naval Postgraduate School, December 2009.
Thesis Advisor(s): Dew, Nicholas. Second Reader: Hudgens, Bryan. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Lighting, LEDs, shipboard lighting. Includes bibliographical references (p. 31-32). Also available in print.

Thesis (Master of Business Administration)--Naval Postgraduate School, December 2009.
Thesis Advisors: Dew, Nicholas ; Mutty, John. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: LED lighting, solid state lighting, business case analysis. Includes bibliographical references (p. 81-83). Also available in print.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.
Includes bibliographical references (p. 37-40).
One important component in energy usage is lighting, which is currently dominated by incandescent and fluorescent lamps. However, due to potentially higher efficiencies and thus higher energy savings, solid-state lighting (SSL) is seriously being considered as a replacement. Currently, state-of-the-art white LEDs are made up of thin films of GaN and InGaN grown on sapphire substrates. A new LED structure design is proposed, in which GaN nanorod arrays are grown on silicon substrates. This new structure could be fabricated using anodized aluminum oxide's (AAO) ordered arrangement of pores as a template for growth of the nanorod array. AAO is selected for its high porosity and simple controllability of pore size and separation, which can in turn produce high density monocrystalline nanorod arrays with adjustable rod size and separation. Several advantages are enjoyed by LEDs based on rod arrays: lower cost, better yield and reliability and higher efficiencies. Two more LED designs, other than the current state-of-the-art GaN LED and the proposed LED structure, are included for comparisons. It is found that the proposed LED structure design is the best after considering costs and efficiency. For commercialization of this new LED design, the market penetration plan is to have a partnership with one of the major players in the current white LED industry. This has the advantage of having minimal capital investment and the product could be sold under an established brand. A simplified projection of earnings is calculated to illustrate sustainability of this business plan.
by Qixun Wee.
M.Eng.

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006.
Buck, John, Committee Co-Chair ; Ferguson, Ian, Committee Chair ; Krishnamurthy,Vikram, Committee Member ; Chang, Gee-Kung, Committee Member ; Callen, W. Russell Jr., Committee Member ; Summers, Christopher, Committee Member.

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management, 2003.
Includes bibliographical references (p. 106-107).
Geneticists study fruit flies due to their rapid lifecycles. Therefore, it follows that those interested in disruptive innovation study technologies with fast moving clock speeds. The pace of technology in solid state lighting (SSL) is an excellent subject for that purpose. Wherever one looks today, this technology, which has actually been with us since the early 1960's, is quickly affecting our lives. New traffic signals, architectural lighting solutions, theater lighting and even lights in our local restaurants are now cool, efficient and pleasing to the eye. This thesis is intended to establish the state of the art of SSL and to provide a palette for future scenarios and ways to navigate the coming changes. The crux of the discussion is to provide considerations for managers faced with rapidly evolving technologies. Two richly detailed scenarios for the future of SSL are presented. After an analysis of the industry, a template for resolving a product portfolio with explicit examples is developed. Using those possible products as a launching platform, basic foundations of several possible business plans lay the groundwork for the next steps of a firm considering entry into the SSL industry. Finally, lessons for managers participating in rapidly innovating industries are discussed.
by Edward Alan Dowdell.
M.B.A.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2006
The electrical supply utility, ESKOM, cannot cope with the growing demand in South Africa. This results in load shedding and power outages. This capacity can be augmented, by conducting energy audits, retrofitting government buildings, designing and installing cost-effective lighting systems, and using renewable energy sources in rural areas. Households in rural areas depend on candles and paraffin lamps to supply light at night. Solar panels as renewable energy sources are very expensive in conventional lighting systems. The problem is that a cost-effective, affordable lighting system has not yet been designed. The following four projects have been completed by the author: - Software development for a lighting design in general - Efficient high bright light emitting diode (HB-LED) lighting system - Energy audit and retrofit of the Nuwe Hoop School in Worcester - Optimization of hybrid solar-diesel system Firstly, the author wrote a program that is used in lighting designs. This illumination software is utilized for educational purposes. A manual step-by-step lighting design procedure was compiled. The JAVA object-oriented programming language was used to write the code of the design software. Real life design parameters are fed to the program, to confirm proper implementation. The software package will perform illuminance calculations to display relevant Isolux diagrams for educational purposes.

A novel solid state illumination source has been developed. A two terminal dual LED has been created with the ability to control the relative intensities of the two emission peaks by varying drive current. Doping profiles have been used to extend the dynamic range of the dual LED over other reported devices. Operation of the dual LEDs is explained as a function of drive current. In addition, novel use of phosphor mixtures allows the creation of a broadband spectral power distribution that can be varied using a dual LED as an excitation source. Combinations of phosphors that have varied excitation spectra provide the ability to selectively excite different phosphors with the different LED emission peaks. First and second generations of the two terminal dual LED and the phosphor combination are discussed. The final source has the ability to mimic the light of a blackbody radiator over a range of 3200 K - 5300 K. The development of a three terminal dual LED as a pump source was prohibited by the need for a III-nitride tunnel junction, that proved unattainable in the scope of this work. However, several novel doping schemes were investigated toward this end. Finally, a circadian light source has also been developed that can affect physiological changes in humans, and a light box for entrainment of circadian rhythms in rats has been built.

The thesis is aimed at the investigation of niche applications of solid-state lighting with controllable colour-rendition, spatial, photochemical, and photobiological properties. In order to employ the controllability of light emitting diode (LED) based lighting technology, the research on such niche applications as artwork illumination and street lighting are focussed. The smart colour rendition engine (CRE), which allows for continuously tuning metameric spectra with different colour rendition properties, is introduced. The results on the subjective validation of the statistical colour rendition metric using the CRE are presented. The main requirements for artwork illumination are overviewed and the application of the intelligently controlled CRE in artwork illumination is investigated in two aspects: a) the establishment of subjective needs in colour quality of illumination as a function of the contents of artworks and the observers’ cultural background and b) the effect of the control of photochemical damage irradiance on the visual impression from artworks, while adjusting the chromaticity and colour rendition properties of the illuminant. The results on the optimization of the luminance distribution within an intelligent lighting installation for pedestrian areas using the identification of subjective impressions are presented. The low-circadian action LED source for outdoor lighting is introduced and the results on the assessment of photometric, colorimetric... [to full text]
Ši disertacija yra skirta ištirti kietakūnio apšvietimo su valdomomis spalvų perteikimo, erdvinėmis, fotocheminėmis ir fotobiologinėmis savybėmis galimus nišinius taikymus. Kaip nišinių taikymų pavyzdžiai, kuriuose ryškiausiai atsiskleidžia valdomo apšvietimo privalumai, buvo pasirinkti dailės kūrinių apšvietimas ir gatvių apšvietimas. Šiame darbe pristatytas išmanusis spalvų perteikimo variklis (SPV), leidžiantis tolydžiai keisti metamerinius spektrinės galios skirstinius, pasižyminčius skirtingomis spalvų perteikimo savybėmis. Naudojant SPV validuotas statistinis apšvietimo spalvinės kokybės vertinimo metodas. Apžvelgti dailės kūrinių apšvietimo reikalavimai bei pristatomi SPV pritaikymo dailės kūrinių apšvietimui pagal du kriterijus tyrimai: a) įvertinant apšvietimo spalvinei kokybei teikiamos subjektyvios pirmenybės priklausomybę nuo dailės kūrinio turinio ir žiūrovų kultūrinės kilmės; b) parodant regimosios išraiškos pokytį, atsirandantį dėl apšvietos lygio kitimo, kuomet fiksuojama apšvietimo fotocheminė įtaka apšviečiantiems paviršiams, kintant kokybiniams apšvietimo parametrams. Pristatomi apšvietimo skirstinio pėsčiųjų zonai optimizavimo rezultatai, gauti įvertinus subjektyvius poreikius. Pasiūlytas žemo cirkadinio poveikio kietakūnis šviesos šaltinis, skirtas lauko apšvietimui. Įvertintos tokio šaltinio fotometrinės, kolorimetrinės, spalvų perteikimo, fotobiologinės ir šviesinės taršos savybės bei atlikti tyrimai, įvertinantys psichofizines savybes.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第15468号
人博第498号
新制||人||122(附属図書館)
21||人博||498(吉田南総合図書館)
27946
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 田部 勢津久, 教授 杉山 雅人, 准教授 木下 俊哉
学位規則第4条第1項該当

Si QDs embedded in SiOx or SiNx thin films, which could emit light in the entire visible range from 440 nm to 840 nm by controlling their size and/or their matrix, were synthesized by evaporation or plasma enhanced chemical vapor deposition techniques. Various shades of white could be obtained from multi-layered SiNx film structures by controlling the size of Si QDs and layer thickness. It was shown that the combination of these films can produce white emission spectra with superior color rendering properties compared to conventional fluorescent tubes. Such Si-based QDs can be used as down-converting phosphors to coat a blue/UV LED to generate white light, providing a less expensive fabrication process to obtain advanced solid state lighting devices. As a supplement, free CdTe QDs with emission colors spanning 520~700 nm and quantum efficiency up to 54%, were synthesized using a colloidal chemical method for white LED applications. White PL and a range of emission colors were obtained from mixed CdTe QD samples excited by a 420 nm blue LED. Another part of this research was to develop a new x-ray powder phosphor, ZnTe:O, for biological imaging applications used in CCD-based synchrotron x-ray detectors. A unique dry synthesis process, including gaseous dry doping and etching procedures, was developed to synthesize ZnTe:O phosphors. The excellent x-ray luminescence results of oxygen doped ZnTe, including high efficiency, high resolution, fast decay, low afterglow and an improved spectral match to the CCD detector, indicated that ZnTe:O is a promising phosphor candidate for x-ray imaging applications.

An Investigation into Red Emitting Phosphors for Display and Lightings Two very different classes of red phosphors were evaluated in this thesis; sulphide based phosphors (CaS:Eu2+) and phosphors based on the formulae:- LiEu1- xMx(MoO4)2-y(WO4)y, [M=Al3+, Y3+ and Gd3+]. CaS:Eu2+ was coated with Al2O3 using atomic layer deposition technique and placed into a humidity chamber at high temperature and high humidity for a period of time. The emission spectra were measured and evaluated against uncoated CaS:Eu2+. The results from the humidity tests revealed that Al2O3 coated CaS:Eu2+ increased the life span of the phosphor and therefore can be the potential use for the purpose of application at moderate humidity and temperature. For the phosphors based on LiEu1-xMx(MoO4)2-y(WO4), all the findings reported herein showed that, depending upon the types of cations introduced to the host lattices, incorporation of M at some point offered very much the same or better luminous efficacy when compared to the parent compound with 100 mol% of Eu3+. This work also attempted to examine the correlative relationship between the crystal structures and the luminous efficacies although some attempts were unsuccessful. The findings discovered within this research are beneficial for solid state lighting industries where the cost of using rare earth metals has become significant and recycling is difficult.

Ši disertacija yra skirta ištirti kietakūnio apšvietimo su valdomomis spalvų perteikimo, erdvinėmis, fotocheminėmis ir fotobiologinėmis savybėmis galimus nišinius taikymus. Kaip nišinių taikymų pavyzdžiai, kuriuose ryškiausiai atsiskleidžia valdomo apšvietimo privalumai, buvo pasirinkti dailės kūrinių apšvietimas ir gatvių apšvietimas. Šiame darbe pristatytas išmanusis spalvų perteikimo variklis (SPV), leidžiantis tolydžiai keisti metamerinius spektrinės galios skirstinius, pasižyminčius skirtingomis spalvų perteikimo savybėmis. Naudojant SPV validuotas statistinis apšvietimo spalvinės kokybės vertinimo metodas. Apžvelgti dailės kūrinių apšvietimo reikalavimai bei pristatomi SPV pritaikymo dailės kūrinių apšvietimui pagal du kriterijus tyrimai: a) įvertinant apšvietimo spalvinei kokybei teikiamos subjektyvios pirmenybės priklausomybę nuo dailės kūrinio turinio ir žiūrovų kultūrinės kilmės; b) parodant regimosios išraiškos pokytį, atsirandantį dėl apšvietos lygio kitimo, kuomet fiksuojama apšvietimo fotocheminė įtaka apšviečiantiems paviršiams, kintant kokybiniams apšvietimo parametrams. Pristatomi apšvietimo skirstinio pėsčiųjų zonai optimizavimo rezultatai, gauti įvertinus subjektyvius poreikius. Pasiūlytas žemo cirkadinio poveikio kietakūnis šviesos šaltinis, skirtas lauko apšvietimui. Įvertintos tokio šaltinio fotometrinės, kolorimetrinės, spalvų perteikimo, fotobiologinės ir šviesinės taršos savybės bei atlikti tyrimai, įvertinantys psichofizines savybes.
The thesis is aimed at the investigation of niche applications of solid-state lighting with controllable colour-rendition, spatial, photochemical, and photobiological properties. In order to employ the controllability of light emitting diode (LED) based lighting technology, the research on such niche applications as artwork illumination and street lighting are focussed. The smart colour rendition engine (CRE), which allows for continuously tuning metameric spectra with different colour rendition properties, is introduced. The results on the subjective validation of the statistical colour rendition metric using the CRE are presented. The main requirements for artwork illumination are overviewed and the application of the intelligently controlled CRE in artwork illumination is investigated in two aspects: a) the establishment of subjective needs in colour quality of illumination as a function of the contents of artworks and the observers’ cultural background and b) the effect of the control of photochemical damage irradiance on the visual impression from artworks, while adjusting the chromaticity and colour rendition properties of the illuminant. The results on the optimization of the luminance distribution within an intelligent lighting installation for pedestrian areas using the identification of subjective impressions are presented. The low-circadian action LED source for outdoor lighting is introduced and the results on the assessment of photometric, colorimetric... [to full text]

Ce mémoire s'inscrit dans la construction d'une méthodologie d'analyse de défaillance pour l'évaluation de la fiabilité de diodes électroluminescentes, par une approche basée sur l'analyse physique de dégradation et l'extraction de signatures électriques de défaillance et optiques pour localiser les zones dégradées. L'ajout d'analyses physico-chimiques réduit le nombre de composants et peut confirmer les mécanismes de dégradation induits par les vieillissements en stockage actif. Un projet, en collaboration avec le CNES, a permis la mise en évidence des zones sensibles de DELs à MPQ InGaN/GaN à faible puissance (30mW) soumises à un vieillissement en conditions opérationnelles (1500h/85°C/Inominal). L'analyse de défaillance de ces DELs a permis d'expliquer une perte de 65% de puissance optique par la modification de la structure moléculaire de l'huile silicone activée photothermiquement induisant une perte de fluorescence de 69% et une très forte diminution de l'absorption de la lumière de la DEL (90%). Nous avons également démontré (projet CEA-LETI - éclairage public) que le même mécanisme est présent dans le mélange gel silicone/phosphore YAG:Ce de DELs blanches à MPQ InGaN/GaN soumises à un vieillissement similaire (85°C/550mA/500h). A 450nm, le rendement de fluorescence a augmenté de 1,2% malgré des pertes en absorption (> 94%) et en réémission de fluorescence (> 85%). La modification de la structure moléculaire du gel a induit une perte de puissance optique des DELs de 45% et une dérive de la couleur blanche vers le jaune (≈ 3,6%). Cette dérive est due à un décalage spectral de la fluorescence de l'UV (5nm) vers le bleu entraînant un décalage vers le rouge (2nm) de la lumière de la DEL.

This work specifies the synthesis and the characterization of amorphous powders belonging to the Y2O3 - Al2O3 - B2O3 system. The main objective of this work was to develop amorphous powders near the YAl3(BO3)4 composition without any rare earth as doping for the development of a new family of phosphors for solid state lighting systems excited by near ultra-violet light. The sol-gel and polymeric precursor methods were applied in order to produce these powders. After these syntheses we optimized several parameters such as thermal treatments: two different routes were tested: direct calcination and pyrolytic decomposition followed by calcination. The temperature, annealing time, heating rate and the effects of impurities on the photoluminescence (PL) were studied. A comparison between these two synthesis methods was done. The powder samples were characterized by thermal analysis technique, X-ray diffraction, photoluminescence and infra-red spectroscopies, transmission and scanning electron microscopy, elemental analysis and electron probe microanalyses, nuclear magnetic resonance, cathodoluminescence, electronic paramagnetic resonance. From the thermal analyzes, it was observed that the powder prepared by polymeric precursor method shows a glass transition temperature (Tg) around 740 °C and crystallization temperatures (Tx) at 815, 850 and 900 °C. Amorphous powder showing high photoluminescence emission (between 400 and 750 nm) and quantum yields higher than 90% at 365 nm excitation, without any phase segregation were obtained when the samples are annealed at temperatures at around Tg, above this temperatures the powder start to crystallize decreasing their PL properties. Other compositions were studied by increasing the relative amounts of Y2O3, Al2O3 and B2O3, by removing the yttrium, addition of SiO2. Finally, the first measurements of color coordinates and the preliminary tests on the thermal and photo stability have been done
Ce travail de these porte sur la synthèse et la caractérization de poudres amorphes en appartenant système Y2O3 - Al2O3 - B2O3. L'objectif principal du travail a été de préparer des poudres amorphes dont la composition est proche de YAl3(BO3)4 sans terre rare en vue la réalisation de phosphores pour des dispositif d'éclairage solide à base de LED emmetant dans le proche UV. Pour la synthèse des poudres les methodes sol-gel et celles des precurseurs polymériques ont été utilisées. Nous avons ensuite optimizé les paramètres thermiques, en utilisant deux stratégies: la calcination directe et la pyrolyse suivrie d'une seconde étape de calcination. La température, le temps de recuit, vitesse de chauffage et les effect des impurities sur la photoluminescence ont été étudié. Les échantillons en poudre ont été caractérisés par les techniques d'analyse thermiques, diffraction des rayons X, la spectroscopie de photoluminescence et la spectroscopie infra-rouge, microscopies électronique à balayage et en transmission, les méthodes des analyses élémentaire et microsonde électronique, la résonance magnétique nucléaire, cathodoluminescence et le résonance paramagnétique électronique. Par l'analyse thermique, on a observé que la poudre préparée par la méthode de précurseur polymère a une température de transition vitreuse (Tg) autour de 740 ° C et des températures de cristallisation (Tx) à 815, 850 et 900 ° C. Les poudres amorphes presentent de larges bandes d'émission de photoluminescence (entre 400 et 750 nm) avec des rendements quantiques supérieurs à 90% pour une excitation de 365 nm. De plus, les poudres microscopiques obtenu sont chimiquement homogene avec des composition très proche de celle initialmente visée YAl3(BO3)4 lorsque les échantillons sont recuits à des températures voisine du Tg. Au-dessus de cette température, la poudre commence à se cristalliser conduisant à réduction de l'intensité de PL. D'autres compositions ont été étudiées en augmentant la quantité relative de Y2O3, Al2O3 et B2O3, en éliminant complètement l'yttrium, ou en ajutant SiO2. Finalement, les premiers mesures de coordonnées de couleur et les essais préliminaires sur la stabilité thermique et photométrique sont très prometeur. En effet, outres les rendemente specifiques de luminescence très elevés ces luminophores émitent de lumiére très chaudes

Ce mémoire s'inscrit dans la construction d'une méthodologie d'analyse de défaillance pour l'évaluation de la fiabilité de diodes électroluminescentes, par une approche basée sur l'analyse physique de dégradation et l'extraction de signatures de défaillance électriques et optiques pour localiser les zones dégradées. L'ajout d'analyses physico-chimiques réduit le nombre de composants et peut confirmer les mécanismes de dégradation induits par les vieillissements en stockage actif. Un projet, en collaboration avec le CNES, a permis la mise en évidence des zones sensibles de DELs à MPQ InGaN/GaN à faible puissance (30mW) soumises à un vieillissement en conditions opérationnelles (1500h/85°C/Inominal). L'analyse de défaillance de ces DELs a permis d'expliquer une perte de 65% de puissance optique par la polymérisation de l'huile silicone activée photothermiquement induisant une perte de fluorescence de 69% et une très forte diminution de l'absorption de la lumière de la DEL (90%). Nous avons également démontré (projet CEA-LETI  éclairage public) que le même mécanisme est présent dans le mélange gel silicone/phosphore YAG:Ce de DELs blanches à MPQ InGaN/GaN soumises à un vieillissement similaire (85°C/550mA/500h). A 450nm, le rendement de fluorescence a augmenté de 1,2% malgré des pertes en absorption (> 94%) et en réémission de fluorescence (> 85%). La polymérisation de l'huile silicone a induit une perte de puissance optique des DELs de 45% et une dérive de la couleur blanche vers le jaune (≈ 3,6%). Cette dérive est due à un décalage spectral de la fluorescence de l'UV (5nm) vers le bleu entraînant un décalage vers le rouge (2nm) de la lumière de la DEL
GaN-based LEDs are currently used in a wide range of applications as solid-state lighting, backlighting or full-color displays. Up to date, polymer-based packaging degradation mechanisms are not fully understood. The purpose of this thesis is to work out a methodology of failure analysis contributing towards reliability estimation of GaN-based LEDs under active storage ageing tests. The methodology consists in extracting electro-optical failure signatures to locate degraded zones. A second step is based on physico-chemical analyses used to both confirm failure mechanisms and reduce the number of components to study. Environmental ageing tests (1500h/85°C/Inominal) have been performed on low power InGaN/GaN MQW LEDs (30mW) through a project in collaboration with the French Space Agency (CNES). A 65% loss of optical power has been reported after ageing. Through the methodology, we have found out that optical loss is due to the silicone oil (i.e. chip coating) polymerization activated by photothermal mechanism thereby involving both a 69% fluorescence emission loss and a strong decrease of LED light absorption (90%). A similar failure mechanism has been reported on YAG:Ce/silicone oil mixture located in phosphor converted high power white InGaN/GaN MQW LEDs (CEA-LETI collaboration - Solid-State Lighting project). Fluorescence efficiency has increased (1,2% at 450 nm) despite both strong absorption (94%) and fluorescence emission (85%) losses. Actually, silicone oil polymerization has induced a 45% loss of optical power and a 3,6% yellow shift of white light. Such drift has been linked to both a 5nm blue shift of UV fluorescence involving a 2nm red shift of LED light

Ces travaux de thèse portent sur l'évaluation des propriétés de nanofils InGaN/GaN en vue de la réalisation de diodes électroluminescentes (LEDs). Deux types d'architecture, obtenus par des techniques de croissance différentes, ont été étudiés. La technique MBE a conduit à la réalisation de LEDs en structure axiale émettant du domaine spectral bleu au rouge. Les émetteurs uniques présentent dans ce cas des diamètres typiquement inférieurs à 100 nm. La technique MOCVD a conduit quant à elle la fabrication de LEDs émettant des longueurs d'onde plus courtes à partir d'hétérostructures InGaN/GaN en Coeur/Coquille présentant des dimensions micrométriques. Dans les deux cas, la croissance est réalisée de manière spontanée sur un substrat Silicium (111) de conductivité élevée permettant l'injection verticale du courant dans les dispositifs intégrés à l'échelle macroscopique. L'ensemble des briques technologiques nécessaires à la fabrication de LEDs a été évalué par un panel important de techniques expérimentales adaptées aux structures à fort rapport de forme. Ainsi, l'effet de l'incorporation d'espèces dopantes de type n (Silicium) et de type p (Magnésium) a été caractérisé par des expériences de spectroscopie optique couplées à des mesures électriques sur fils uniques. De plus, la cathodoluminescence basse température a été largement utilisée afin d'étudier les propriétés optiques de la zone active à base d'InGaN dans les deux architectures considérées. Après intégration technologique, des caractérisations électro-optiques résolues à l'échelle du fil unique ont montré que les performances des LEDs à nanofils restent principalement limitées par la fluctuation des propriétés électriques et optiques entre émetteurs uniques
This thesis aims at studying the intrinsic properties of InGaN/GaN nanowires (NWs) in order to fabricate efficient light emitting diodes (LEDs). Two active region designs, obtained through different growth techniques, have been extensively investigated. Axial NW-based LEDs emitting from the blue to the red spectral range have been grown by MBE. In this case, single emitters present diameters typically smaller than 100 nm. MOCVD allowed the fabrication of LEDs emitting shorter wavelengths from Core/Shell heterostructures with typical dimensions in the micrometre range. In both cases, the spontaneous growth has been conducted on Silicon (111) highly conductive substrates in order to inject the current vertically into macroscopically contacted devices. Technological building blocks needed to fabricate LEDs have been investigated using a wide range of characterization techniques adapted for high aspect ratio structures. Thus, n-type (Silicon) and p-type (Magnesium) dopings have been assessed thanks to optical spectroscopy techniques, and these results have been confirmed by electrical measurements carried out on single wires. Furthermore, low temperature cathodoluminescence has been widely used to study the optical properties of InGaN-based active regions. After technological integration, electro-optical characterizations with spatial resolution down to the single wire level have revealed that device performances are mainly limited by the fluctuation of electrical and optical properties between single emitters

Main aim of this work was the fabrication and characterization of polymeric TiO2 hybrid nanocomposites. When dispersed at the nanoscale level, TiO2 can tune the optical properties of the polymeric matrix, such as the UV absorption and the increase of refractive index, preserving the transparency in the visible and the flexibility of the polymer. TiO2 nanopaticles were modified on the surface with different molecules; they were then dispersed in MMA and polymerized in bulk, in order to obtain optically transparent TiO2/Poly-methylmethacrylate (PMMA) sheets. The application of these objects was in the solid-state lighting field, where the nanoparticles play the role of light diffusers according to Rayleigh Scattering. Films based on poly 2-ethyl-2-oxazoline (PEOX) and TiO2 nanoparticles with concentrations up to 44 % in weight were also prepared by casting from water solutions. Nanocomposites films remained highly transparent in the visible, and absorbed UV radiation up to the proximity of the visible range. The refractive indices of the films raised from about 1.52 to 1.65 with increasing of TiO2 concentration. The good optical properties and the solubility in water of these materials could allow their application in the paint and coating industry, and in the field of conservation of cultural heritage as consolidants or varnishes of paintings.

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No intuito de aportar contribuições ao uso de diodos emissores de luz (ou LEDs, do inglês Light Emmiting Diodes) em sistemas de iluminação pública, cobrindo lacunas existentes no cenário nacional, este trabalho traz uma ampla análise sobre este tema. São apresentados conceitos básicos da fotometria clássica e um estudo sobre adaptações da fotometria para baixos níveis de luminância, que é a condição observada nas vias públicas durante o período noturno. Propõe-se a utilização de métricas escotópicas em sistemas de iluminação pública, uma vez que estas melhor representam a real sensação visual (se comparadas às métricas clássicas – fotópicas) nas condições de iluminamento típicas observadas nestes sistemas. Aspectos gerais da iluminação pública e um histórico da evolução do sistema nacional são brevemente apresentados bem como uma discussão sobre a situação atual deste sistema e das tecnologias utilizadas. O trabalho traz também um estudo sobre características ópticas, elétricas e mecânicas dos LEDs e uma análise dos diferentes tipos de LEDs brancos mais utilizados (HB – High Brightness – e HP – High Power – LEDs). Algumas normas e recomendações aplicáveis à utilização de LEDs em iluminação pública são analisadas e discutidas, com o intuito de se investigar lacunas ainda não cobertas pela normatização existente. Análises de resultados de ensaios de laboratório e de campo, inéditos no país, realizados com alguns modelos de luminárias LED para iluminação pública disponíveis no mercado, são também apresentadas. Um estudo sobre acionamento de LEDs é realizado, abordando técnicas de equalização de corrente entre arranjos série de LEDs associados em paralelo e diferentes tipos de circuitos de acionamento para LEDs. São propostas, analisadas e implementadas uma estrutura inédita de baixo custo para a equalização de corrente e um circuito para o acionamento de LEDs baseado na integração de dois conversores cc cc não isolados. A topologia de dois estágios proposta é composta por um conversor boost no primeiro estágio, utilizado para a correção do fator de potência e por um conversor buck no segundo estágio, utilizado para o controle da corrente nos LEDs. Por fim, o acompanhamento da implantação e do desempenho, ao longo de dez meses, do projeto piloto de iluminação pública empregando LEDs instalado no anel viário da Faculdade de Engenharia da UFJF é apresentado.
In order to present contributions to the use of light emitting diodes (LEDs) in public lighting systems, covering gaps on the national scenario, this work encompasses abroad analysis related to this issue. Basic concepts of classical photometry are presented and so a study of photometry’s adaptations for low luminance levels. It is proposed the use of scotopic metrics for street lighting systems, since they can better represent the actual visual sensation (when compared to the classical one – photopic metrics) on its typical nighty conditions. General aspects of street lighting and the history of the national’s public lighting system are briefly presented as well as a discussion about the current situation of the Brazilian system and technologies adopted. The work also brings a study of mechanical, electrical and optical characteristics of LEDs and an analysis of the two different types of commonly used white LEDs (HB – High Brightness – and HP – High Power - LEDs). Some standards and recommendations related to the use of LEDs in street lighting are analyzed and criticized, with the aim of show some gaps not yet covered by the existent standards. An unprecedented analysis regarding laboratory and field test benchmarking, taken for some luminaires available in commerce, is also presented. A study of LED driving is presented, covering equalization techniques for parallel LEDs strings and different types of LED driving circuits. It was proposed, analyzed and implemented a novel and low cost structure for current equalization and an LED driver, based on the integration of two non-isolated dc dc converters. This proposed two stages topology is composed by a boost converter, on the first stage, employed to the power factor correction and a buck converter, on the second stage, to control the LED’s current. Finally, the process of monitoring the installation and the performance, during ten months, of the LEDs public lighting pilot project, on the roadway belt of Engineering Faculty of UFJF is presented.

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Cresce a cada dia o n úmero de cargas não lineares conectadas aos diversos sistemas el étricos, seja em ní vel de transmissão ou distribui ção. Como consequência desse crescimento, e possí vel encontrar casos de consumidores enfrentando problemas relacionados a desarmes de disjuntores e sobreaquecimento de condutores, entre outros efeitos indesejados. Tomando um desses casos como base para este estudo, esta disserta ção tem o objetivo de avaliar e propor uma solu ção para uma rede monof asica real, que possivelmente e comum a outros consumidores. A carga monof ásica composta por lumin árias a LED (t picas cargas não lineares) e cargas indutivas se apresenta aos terminais da fonte com um comportamento de elevado conte udo harmônico (THD) de corrente e baixo fator de potência. Essa condi ção adversa pode ser mitigada de diversas maneiras, como por exemplo pela a ção de um fi ltro passivo,fi ltro ativo ou ainda fi ltro h brido (o qual e composto por uma combina ção dos dois primeiros). Ser a proposto nesta disserta ção uma metodologia de projeto relacionada a aplica ção de um fi ltro hi brido monof ásico visando corrigir o fator de potência e reduzir o conte udo harmônico de corrente presente na fonte, tomando como base as caracterí sticas do sistema avaliado em uma ind ústria gr áfi ca t ípica. Serão investigadas algumas con gura ções de filtros com o objetivo de mitigar problemas de Qualidade de Energia El étrica. Como consequência, ser a desenvolvida a an álise matem atica da topologia adotada e o projeto do controlador, baseado em um controlador proporcional-ressonante e na Teoria p-q Monof asica. A veri ca ção da solu ção proposta e sustentada pelos resultados de simula ção obtidos via software PSIM.
The amount of non-linear loads connected to the various electrical systems grows on a daily basis, regardless those loads are tied to a transmission or distribution bar. As a consequence of this growth, it is possible to nd cases of consumers facing problems such as tripping of breakers and cables overheating, among other undesired e ects. Taking one of these cases as the focus of this study, this dissertation aims to evaluate and propose a solution to a real single-phase system, which could be considered similar to other consumers. The single-phase load composed of LED luminaires (typical non-linear load) and inductive loads presents high THD and low power factor behavior at source terminals. This condition can be mitigated by using some well-known techniques, such as passive lters, active lters or hybrid lters, (which are composed by the combination of the former two). This Master document Thesis proposes a design methodology of a single-phase hybrid lter aiming power factor correction and reduction of the harmonic content of the current delivered by the AC power supply when feeding a typical printing factory. It will be reviewed and discussed some possible lter con gurations aimed to solve the case under evaluation. It is also included the mathematical analysis of the proposed topology, along with the design of the control system of the inverter. The Single-Phase p-q Theory is reviewed in order to design the control. The closed-loop control is desinged by a proportional-resonant compensator. Simulation results, by employing the PSIM software, are provided aiming to validate the solution proposed.

This work consists of the study, design and implementation of DC-DC converters, used in lighting systems based on light emitting diodes (LEDs). Can be powered by an universal AC voltage source or battery, and the current in the LEDs is controlled digitally. The main objective is to present a proposal of new step-up/down converters topologies with full conversion much higher than that of conventional converters. So, is initially presented an overview of solid-state lighting (SSL). Following is presented the study on the dynamic behavior of converters based on modeling by the method of varying state-space average, ending with the design of a digital PI controller. This work resulted in the application for a patent PI-0801425-6 filed with the INPI, which presents a new family of converters with full conversion extremely wide, called cubic converters.
O presente trabalho consiste do estudo, projeto e implementação de conversores CCCC, aplicados em sistemas de iluminação de estado sólido baseado em diodos emissores de luz (LEDs). Podem ser alimentados por uma fonte de tensão alternada universal ou por uma bateria sendo que a corrente nos LEDs é controlada digitalmente. O objetivo principal é apresentar uma proposta de novas topologias de conversores abaixadores/elevadores com faixa de conversão muito maior que a dos conversores convencionais. Portanto, inicialmente é apresentada uma visão geral sobre iluminação de estado sólido (SSL). Na sequência, é apresentado o estudo sobre o comportamento dinâmico dos conversores baseado na modelagem através do método de variáveis de espaço de estados médio, finalizando com o dimensionamento de um controlador PI digital. Este trabalho resultou no pedido de patente de invenção PI-0801425-6 depositado junto ao INPI, o qual apresenta uma nova família de conversores com faixa de conversão extremamente larga, denominados de conversores cúbicos.
Doutor em Ciências

De nouveaux complexes de cuivre(I) cationiques de formule générale [Cu(P^P)(N^N)][PF6] où P^P représente un ligand bis-phosphine chélatant, bis-[2- (diphenylphosphino)phenyl]ether (DPEPhos) et N^N, des ligands 2,2-bis-pyridyls ont été développés. Les complexes ont montré des émissions à l’état solide couvrant tout le spectre du visible et la présence de la fluorescence retardée activée thermiquement (TADF) a été démontrée. Ces complexes ont été évaluées dans des cellules électrochimiques luminescentes (LECs) et ont conduit aux LECs émettant dans de différentes couleurs, i.e., bleue, verte, jaune, orange, rouge, et enfin des LECs blanches
New cationic copper(I) complexes with the general formula of [Cu(P^P)(N^N)][PF6] where P^P is a chelating bis-phosphine ligand bis-[2-(diphenylphosphino)phenyl]ether (DPEPhos) and N^N 2,2-bis-pyridyl ligand derivatives were developed. The complexes featured solid-state emissions covering the entire visible spectrum and the presence of the thermally activated delayed fluorescence (TADF) was demonstrated. Furthermore, the complexes were incorporated in light-emitting electrochemical cells (LEC) and led to devices emitting in different colors, i.e., blue, green, yellow, orange, red, and ultimately white-emitting LECs

The International Energy Agency estimated that lighting accounts for ~19% of the total worldwide energy consumption. Light emitting diodes (LEDs) have higher efficiency compared to that of conventional lighting sources. The commercial white-LEDs (WLEDs) are based on broad-band Y3Al5O12:Ce3+ (YAG:Ce) yellow phosphor in combination with blue LED chips through a low cost and simple procedure, in which the YAG:Ce phosphor is directly packed on the blue InGaN chip. However, such two colour-based WLEDs exhibit poor colour rendering index (CRI, usually <75), high correlated colour temperature (CCT, >6500 K), and chromaticity drifts, which cannot fully satisfy the applications of lighting and backlighting of the displays. Also, LEDs still face some other drawbacks such as the relatively low efficient green emission, termed the ³green gap´ issXe. A promising alternative strategy is based on the downshift of the electroluminescence of near ultra-violet (NUV)/blue LEDs into the green spectral region by UV/blue-down shifting phosphors. Thus, novel efficient white and green-emitting materials for the phosphor-converted LED applications are required. In this thesis, organic-inorganic hybrids (ureasils, d-U(600)) doped with green emitting Tb3+-based complexes were applied in combination with NUV-LED chips to fabricate efficient green LED prototypes. To improve CRI and CCT of commercial WLEDs, novel blue-light excited La2Ce2O7:Eu3+ red phosphors were also successfully synthesised and characterized. Moreover, tuned white light emitters involving d-U(600) hybrids doped with lanthanide (Ln3+=Tb3+, Eu3+)-based complexes, fluorescent dyes (e.g. coumarin), and carbon dots were also prepared and optically characterised revealing intriguing CCT, CRI and photostability towards novel WLEDs.
A Agência Internacional de Energia estimou que o sector de iluminação representa cerca de 19% do consumo total de energia mundial. Os díodos emissores de luz (LEDs) têm maior eficiência em comparação com as fontes de iluminação convencionais. Os LEDs brancos comerciais (WLEDs) são baseados na combinação de LEDs azuis baseados em InGaN com o luminóforo Y3Al5O12:Ce3+ (YAG:Ce). Este material, que é um emissor de banda larga na região espectral do amarelo. é depositado de forma simples e a baixo custo sobre o LED azul. No entanto, a emissão deste WLEDs baseia-se na adição de duas cores tendo um índice de reprodução de cor baixo (CRI, geralmente <75), elevada temperatura de cor (CCT, > 6500 K) e variação de cromaticidade, que são claras desvantagens em aplicações de iluminação e retroiluminação. Para além destas desvantagens, estes LEDs ainda apresentam emissão na região do verde relativamente menos eficiente (usualmente designado em linguagem inglesa como ³green gap issue´). Uma estratégia alternativa a estes LEDs baseia-se na utilização de dispositivos emissores nas regiões espectrais do ultravioleta próximo (NUV) e do azul combinados com um material capaz de desviar esta emissão para a região do visível. Assim, novos materiais emissores eficientes quer de luz verde quer de luz branca para as aplicações em LEDs são necessários. Nesta tese, híbridos orgânicos-inorgânicos (ureasils, d-U(600)) dopados com complexos à base de Tb3+ emissores no verde foram combinados com NUV-LED comerciais para fabricar protótipos de LED verdes eficientes. Para melhorar o CRI e CCT dos WLEDs comerciais, novos luminóforos de La2Ce2O7:Eu3+ com emissão no vermelho e excitados com LEDs azuis foram, também, sintetizados e caracterizados. Na parte final da tese discute-se a contribuição de novos materiais emissores de luz branca sintonizável baseados em híbridos d-U(600) dopados com complexos de iões lantanídeos (Ln3+=Tb3+, Eu3+), corantes fluorescentes e pontos de carbono com propriedades óticas (CCT, CRI e fotoestabilidade) melhoradas, face ao estado da arte.
Programa Doutoral em Ciência e Engenharia de Materiais

Inorganic-organic semiconductor heterostructures have been subjects of interest for solid-state lighting (SSL) in the last decades due to the potential for simultaneous utilization of the complementary favorable properties of two distinct material classes for producing light. This work proposes a hybrid composite active layer design for light emission which combines inorganic and organic semiconductors. Particular to this composite design, light- emitting organic semiconductor molecules are embedded in an ambipolar charge- transporting inorganic semiconductor matrix. The embedded molecules serve as the radiative recombination sites for charge carriers that are injected into the matrix. Coming up with a composite layer may seem to be just a plug-and-play of different inorganic and organic semiconductor combinations. However, there are several fundamental requirements to make the concept work. Very important factor in realizing high efficiency devices are the properties of the interfaces between the different components because they often govern the physical properties of the overall structure. With this in mind, the energy level alignments at the interfaces of the candidate material combinations and the different chemical interactions taking place at such interfaces were investigated by photoelectron spectroscopy (PES). For the energy level alignment, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the organic dye should be situated in between the valence and conduction bands of the inorganic semiconductor. This alignment provides the necessary energetic driving forces for electron and hole transfers from the charge-transporting inorganic matrix to the light-emitting organic molecules. The PES investigations were focused on the interface formations of these two types of materials in three deposition configurations, namely: the inorganic/organic bilayer, the composite layer and the organic/inorganic bilayer. Additionally, the interface between the inorganic and organic part has to be of high purity and electronic perfection, as otherwise defect states will destroy the coupling of the two materials. By interpreting PES data, we also determined and described the chemical composition of the interface and the resulting coupling of the two materials on the atomic scale. Furthermore, as one of the advantages of hybrid designs, energy transfer from the matrix to the dopant is another possible route for obtaining light emission from the organic dopant. Therefore, another factor to look into would be the resonance between the exciton energies of the inorganic and organic materials. With this in mind and in conjunction with available experimental methods, the room-temperature (RT) photoluminescence (PL) of the hybrid composite active layer was investigated using a high energy laser for exciting the inorganic matrix. The idea here is to exclusively excite the matrix; if there is a light emission coming from the dopant, then it could hint at two possible mechanisms: one is energy transfer and the other is charge transfer from the excited matrix to the dopant. As one of the candidate material combinations, zinc selenide (ZnSe) and a red emitter, Ir(BPA), were investigated. Bilayer and composite thin films of ZnSe and Ir(BPA) organic light emitter were prepared in situ by UHV thermal evaporation technique. The measured energy band alignments for the ZnSe/Ir(BPA) bilayer and ZnSe+Ir(BPA) composite reveal that the HOMO and LUMO of the organic dye are positioned within the ZnSe bandgap. For the initial steps of ZnSe deposition on a dye film to form Ir(BPA)/ZnSe bilayers, zinc atoms were found to intercalate into the dye film leaving behind an excess of selenium at the interface that partly reacts with dye molecules. PES of the composites shows the same chemical species suggesting a similar mechanism. This mechanism leads to composite films with increased content of amorphous phases in the inorganic matrix. The PL spectra of composite films showed a relative enhancement of the emissions coming from the films with low dye concentrations as compared to the films with higher concentrations. This enhancement may hint at a charge transfer and/or an energy transfer from ZnSe to Ir(BPA). Proof of concept for the novel composite design is provided by a device that was fabricated with an active layer that is composed of alternating layer sequences of ZnSe and Ir(BPA). Weak areal emission and red intermittent sparks were visually observed from the device. Overall, several challenges in realizing the hybrid composite active layer design were uncovered during the course of this work. From the results of the PES measurements on several material combinations, it is found that the position of the Fermi level in the pristine inorganic semiconductor and the pristine organic light emitter strongly directs the resulting energy level lineup in the bilayer and composite upon thermodynamic Fermi level equalization at the interfaces. A large interface dipole formation at the material interface can positively reinforce the desired alignment for the proposed composite design. In addition, reactive interfaces of certain compositions are formed rather than the desired abrupt material interface. This reactive interface can hinder efficient charge and energy transfers, impede charge carrier conduction and supply nonradiative recombination sites. Furthermore, alternatives for a less-chemically reactive deposition method are limited by the availability of techniques that are compatible for inorganic-organic layered and composite depositions.

碩士
明新科技大學
光電系統工程系碩士班
105
In order to provide power supply for the dimming circuit, the square wave of regular duty cycle design by 555 non-steady-state circuit is used. In which providingthe buck switching power supply circuit to replace the traditional transformer. To reach the goal of minimizing the weight, improving the efficiency and reducing the heat. Due to the bulkiness of the experimental BUCK switching power supply circuit,we switched to a smaller UCC28880 IC control switching power supply circuit to providepower with the advantage to reduce costs, streamline the circuit, and improve efficiency. This paper presents a light-emitting diode (Light Emitting Diode, LED) lighting device dimmer, can be used for dimming incandescent optical silicon-controlled rectifier (Triode for Alternating Current, TRIAC), the use of pulse width Pulse Width Modulation (PWM) controls the AC power so that the LED does not blink when dimming to low brightness. In the dimming circuit design circuit, the use of 555 monostable circuit PWM modulation is used to adjust the dimming, however in low luminance, there will be flashing phenomenon. To improve this down side, the use of microprocessor with the output of a stable PWM signal will enhance it at low light, making the light source stable and flicker-free phenomenon. In this paper, the product circuit UCC28880 IC design power circuit is used as a voltage source. Bluetooth module and microprocessor combining with an external oscillator output PWM signal are used to control the AC power, also digitally dimming control can be conduct with the use of Bluetooth on mobile phoneincorporating with an App. Keywords: light-emitting diodes, pulse width modulation, switching power supply, Bluetooth.

博士
國立臺灣大學
機械工程學研究所
96
The main purpose of this research is to investigate the control technology of red-green-blue (RGB) light emitting-diode (LED) in order to stabilize luminance and color of lighting. In addition, the well control performance can be provided by knowing of thermal-electric-luminous-chromatic dynamics of RGB LED luminaire. The dynamic model of RGB LED luminaire is a Multi-Input Multi-Output system, and can be divided into three parts as thermal, chromatic and luminous model. Thermal model is derived as fourth-order system, and can be simplified as first-order bi-proper system by using system identification technique. Chromatic and luminous model are zero-th order system due to fast response of photon. The system identification shows that both models are non-linear systems of input power and junction temperature. By knowing the complete thermal-electric-luminous-chromatic model, the control system can thus design by using luminous feedback and junction temperature compensation. In this study, the PI control can satisfy transient specification and reduce luminous steady-state error and color difference. The experimental results showed rise time tr = 0.88s and settling time ts = 2.84s. It also indicated luminous error 0.99％ and color difference Δu′v′= 0.00171 under 15W thermal disturbance. The results prove that the control system can improve RGB LED lighting performance.

碩士
國立臺灣大學
光電工程學研究所
102
In this paper, variable separation mapping design method and solving differential equation method were adopted to obtain freeform surface for a square target plane and circular target plane, respectively. Starting from the freeform lens constructed by these methods, we would keep the light field intensity uniform. We then utilized heterogeneous micro lens array (MLA) to approximate the shape of the freeform lens. We adjusted the curvature radius and size by the simulation results. Through optimization process, we could achieve a uniform light intensity of ight emitting diodes using heterogeneous MLA. The thickness of direct-lit backlight unit is 2 mm thick. This design achieved 96% efficiency and 90% uniformity. It covers an area of 49 square centimeters .