Academic literature on the topic 'SOLID STATE LIGHTING (SSL)'

Light-emitting diodes (LEDs) have been intensively studied for white-light lighting since their luminous efficacy exceeds 50 lm/W. Currently, the luminous efficacy of an LED light tube/bulb is almost above 100 lm/W. LED solid-state lighting (SSL) has unequivocally become the major light source in general lighting. The fact of high efficiency and other advantages of LED SSL is enough to penetrate all lighting scenarios. However, what people demand from new-generation lighting is not only in energy efficiency but also in lighting quality. Thus, how to make the lighting more user friendly is one of the important issues, and, here, optics is the key point. For making a collection with the discussions of the novel optical design in enhancing lighting efficiency in a more uniform illumination pattern, in higher sharpness for special lighting, in a higher signal-to-noise ratio for communication, in more functions for new applications, etc., this Special Issue of “Advanced LED Solid-State Lighting Optics” focuses on advanced applications in all aspects.

The determinants of successful development, commercialization and diffusion of solid state lighting (SSL) are not well understood particularly in a global context. Patent data provide one means to gain insight into corporate and national research and development activities. However, existing SSL patent analyses have focused primarily on United States (US) patents. This study analyzes SSL patents granted worldwide to measure the strengths of US, Japan, Germany, the Netherlands, South Korea, Taiwan, and China, nations all poised to play a key role in SSL's future. It shows a strong and growing role of corporate patent portfolios for firms headquartered in Asian nations. The data cover patents that were applied for and issued from 1937 to March 2009. Our findings suggest a stronger role of non-US organizations and individuals than had been reported in previous studies that focused only on US patents.

Solid-state lighting (SSL) is emerging as a highly competent field and a possible alternative to existing lighting technologies. Development of a suitable phosphor is an important aspect of SSL. The aim of this review is to summarize status of Inorganic Phosphors towards SSL applications. Various examples have been taken from oxide, fluoride, nitride, sulfide and phosphate based host lattices. The important concepts like CIE coordinates and Color Correlated Temperature (CCT) will also be discussed. The sections encompasses of red, blue and green light emitting phosphors. The white light emitting phosphors will also be discussed in details.

AbstractOrganic light-emitting devices (OLEDs) have been widely developed for flat-panel displays, but only recently the efficiency of white OLEDs has risen to the point where they can be considered for solid-state lighting (SSL) applications. In this review, we discuss the requirements of solid-state lighting as they relate to OLEDs. We focus on how the color, efficiency, and cost requirements of general illumination differ from those of displays and how these differences might have an impact on the design of organic SSL. We then present some recent developments in large-area fabrication techniques that might be appropriate for solid-state lighting applications. Finally, we review recent results in the development of organic materials, device architectures, light extraction schemes, and fabrication techniques that can lead to cost-effective OLED lighting.

Recent advances in perovskite nanocrystals-enhanced solid-state lighting (SSL) and liquid-crystal displays (LCDs) are reviewed. We first discuss the development, optical properties, and stability issue of materials, and then we evaluate the performance of SSL and LCDs with perovskite downconverters adopted. In SSL performance evaluation, we investigate the fitting-curve effect in calculations and optimizations where simple Gaussian fitting and precise fitting are compared in detail, and we further optimize for highly efficient, good color-rendering, and human-healthy SSL sources. For LCD performance evaluation, we study the intrinsic tradeoffs between total light efficiency and color gamut coverage. Through optimizations using real line shapes, Rec. 2020 standard coverage as large as 92.8% can be achieved through hybrid integration. Finally, we briefly discuss two future challenges: materials development and device integration. We believe the emerging perovskite nanocrystals are highly promising for next-generation SSL and LCDs.

Nanotechnology has led to a profound paradigm shift after the developments in recent years and after being recognised as one of the most important areas of impending technology. Nanomaterials are the basis of newly emerging nanotechnologies for various applications in sensors, photonics, drug delivery, proteomics, biomolecular electronics, and homeland security. Luminescent nanomaterials have attracted great interest worldwide because of their unusual structural, optical and electronic properties as well as efforts to prepare miniaturised devices. By understanding and manipulating these properties, the performance of the resulting optical structure can be tailored for desired end-use applications. Luminescence nanoparticles have tremendous potential in revolutionizing many interesting applications in today’s emerging cutting-edge optical technology such as solid state lighting. Solid-state lighting (SSL) relies on the conversion of electricity to visible white light using solid materials. SSL using any of the materials (inorganic, organic, or hybrid) has the potential for unprecedented efficiencies. The development of novel mercury-free inexpensive nanomaterials, that convert longer wavelength UV to blue light eventually into white-light and are eco-friendly with improved luminous efficacy, energy-saving, long-lifetime, and low-power consumption characteristics, is discussed. In this review, we present a general description of EL related to nanomaterials as the emitter and outlines basic research requirements that could enable solid-state lighting to achieve its potential. Continuing progress in the synthesis and purification of SSL materials are beginning to enable separation of extrinsic and intrinsic phenomena and improve device performance. This review mainly focuses on the basic mechanism, classification, synthesis and characterization of luminescent nanomaterials. The review also covers recent advances in lanthanide-based nanomaterials and photoluminescent nanofibers formed by combining electrospun polymeric nanofibers and quantum dots (QDs) for lighting applications. In spite of the remarkable scientific progress in preparation processes and applications of nanomaterials, they are still not widely used by the industry. Finally, we conclude with a look at the future challenges and prospects of the development of electroluminescence (EL) devices for lighting.Contents of Paper

The integration of trivalent europium ion (Eu3+)-doped zinc molybdate (ZnMoO4) as red phosphors in next-generation solid-state lighting (SSL) is impeded by their extended electron lifetime and suboptimal thermal stability. To overcome these limitations, we propose a co-doping approach by incorporating Mn2+ and Eu3+ in ZnMoO4, aiming to improve thermal reversibility and reduce the lifetime of electron transitions. A series of Eu3+-doped ZnMoO4 and Mn2+/Eu3+-co-doped ZnMoO4 phosphor materials were synthesized via the conventional sol–gel method, and their photoluminescence properties were compared under high-temperature conditions. Experimental results indicate that the introduction of Mn2+ into Eu3+-doped ZnMoO4 leads to a decrease in quantum efficiency and electron lifetime, primarily attributed to defects within the crystal lattice and energy transfer from Eu3+ to Mn2+, resulting in enhanced non-radiative transitions. However, the addition of a small quantity of Mn2+ remarkably improves the thermal stability and reversibility of the phosphors. Consequently, this co-doping strategy presents a promising avenue for expanding the application possibilities of phosphor materials, particularly for high-power SSL applications subjected to elevated temperatures. Hence, Eu3+-only doped samples are well-suited for lighting applications due to their high IQE and excellent thermal stability. Conversely, Eu3+/Mn2+-co-doped samples show promise in applications that require a shorter electron lifetime and good reversibility.

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.