Rozprawy doktorskie na temat „Rare earth phosphors”

Photovoltaic solar cells can generate electricity directly from sunlight without emitting harmful greenhouse gases. This makes them ideal candidates as large scale future energy producers for the global energy economy. Ideally, solar cells should be efficient and inexpensive to compete in the global energy market. Unfortunately, a number of fundamental limitations exist for the efficiency due to fundamental loss mechanisms of the semiconductor materials used to make solar cells. One of the dominant loss mechanisms from a conventional silicon solar cell is the transparency of sub-bandgap near-infrared photons. Up-conversion is an optical process involving the sequential absorption of lower energy photons followed by luminescence of a higher energy photon. This mechanism could be exploited to minimise photovoltaic sub-bandgap losses. Rare-earth doped materials have ideal up-conversion luminescent properties and have been utilised for many near-infrared to visible applications. This thesis investigates the near-infrared to near-infrared up-conversion processes required for the sub-bandgap photon utilisation within a silicon photovoltaic device. Various sodium yttrium fluoride phosphors doped with rare-earths were characterised theoretically and experimentally. Erbium doped phosphors were found to be ideal for single wavelength power dependent investigations for the non-linear up-conversion processes. The radiative and non-radiative rates of various erbium doped sodium yttrium fluoride phosphors have been approximated and compared with experimental photoluminescence results. These phosphors have been applied to the rear of a bi-facial silicon solar cell and an enhancement in the near-infrared region has been demonstrated. An external quantum efficiency close to 3.4% was measured at 1523nm under 6mW laser excitation. The non-linear dependence on incident pump power has been investigated along with the dominant up-conversion mechanisms involved. It can be concluded that up-conversion phosphors can enhance the near-infrared spectral response of a silicon device. These phosphors have high luminescent efficiencies once up-conversion occurs, but suffer from poor infrared absorption and low up-conversion efficiencies. The results from this study show that relatively high doping levels of selected rare-earths into low phonon energy crystals can improve the absorption and luminescent properties of the phosphor.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第17670号
人博第637号
新制||人||153(附属図書館)
24||人博||637(吉田南総合図書館)
30436
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, 教授 加藤 立久
学位規則第4条第1項該当

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第18380号
人博第693号
新制||人||166(附属図書館)
25||人博||693(吉田南総合図書館)
31238
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 加藤 立久, 教授 杉山 雅人, 教授 森本 芳則, 教授 山本 行男
学位規則第4条第1項該当

Ces travaux de thèse ont pour ambition de proposer des solutions alternatives, aux luminophores avec terres rares, offrant des performances convenables pour des applications dans des dispositifs à LED comme l’éclairage mais également la visualisation ou encore le marquage ou la signalétique. Nous nous sommes intéressés à des luminophores organiques mais également inorganiques tels que les quantum dots (QD). Le problème majeur de ces familles de luminophores est leur instabilité sous contrainte thermique et/ou photonique. Aussi, afin de pallier ce problème nous avons choisi d’utiliser des matériaux inorganiques plaquettaires de type « hydroxyde doubles lamellaires » (HDL) comme matrice hôte du luminophore. Les luminophores étudiés sont la fluorescéine, la sulforhodamine B et des quantum dots InP/ZnS. Plusieurs techniques expérimentales ont été utilisées afin de caractériser leurs propriétés structurales et morphologiques (DRX, SAXS, IR, MEB, MET…). Les propriétés optiques ont également été enregistrées (émission, excitation, rendement quantique de photoluminescence, déclins…). Ces travaux ont mis en évidence la plus-value de la matrice HDL qui permet de reproduire un effet de solvatation pour le luminophore organique ou QD dans une matrice solide et de retrouver des propriétés d’émission semblables à celles de ces luminophores en solution diluée. La dispersion dans une matrice silicone est également favorisée et la stabilité de ces revêtements composites (HDL-Luminophore/silicone) sous différentes contraintes est nettement améliorée
These works have the ambition to offer alternative solutions to phosphors with rare-earth elements, displaying suitable performance for LED devices applications as well as signage or display applications. We have been interested in organic as well as inorganic phosphors such as quantum dots (QD). The main problem encountered with these compounds is their relative instability under thermal and/or photonic stresses. Thus, in order to overcome this issue, we decided to use inorganic materials called layered double hydroxide (LDH) as host matrix to protect these phosphors. Several experimental techniques (XRD, SAXS, IR, SEM, TEM…) have been used to characterize structural and morphological properties. Optical properties have also been recorded (emission and excitation spectra, photoluminescence quantum yields, fluorescence decay…). Using extremely small amounts of phosphors, it is demonstrated here that Zn2Al cation-based LDH tethering acts as a «solid solvent» for the dye, enabling its luminescence even in powder form. Additionally, LDH platelets are found to help the dispersion of the dye or QD in silicone to obtain homogeneous composite films, which exhibit luminescent properties. Finally, the stability of composite coatings (LDH-phosphor/silicone) under different stresses (thermal and photonic) is most often improved

The work in this thesis had two main aims. The first aim was to study the use of a number of precipitation methods to control the size and morphology of precursor phosphor materials for potential applications in a new generation of high definition and field emission displays. The morphological and luminescent characteristics of these precursor phosphor materials were studied after they were annealed to form their respective luminescent oxides using electron microscopy and light measuring techniques. The first set of experiments presented describes the development of a range of spherical submicron europium-doped yttrium oxide phosphor particles and their optimisation for use in the aforementioned applications. A homogeneous precipitation technique exploiting a hydrothermal decomposition of urea that provides hydroxycarbonate phosphor precursor ligands is at the centre of this work. In the presence of rare earth element nitrates the hydroxycarbonate ligands form spherical phosphor precursor particles that after annealing yield the luminescent oxides. This is followed by the presentation of a novel synthetic method using a micellar phase of rare earth element chlorides, after annealing, yielding europium-doped yttrium oxide. This method produces a variety of morphologies with crystallites as small as a few nanometres and up to hundreds of nanometres. Next is described a new precipitation method using ammonia and carbon dioxide gases that are introduced in a controlled manner into a solution of rare earth element chlorides at room temperature. Rare earth element hydroxycarbonates rapidly precipitate upon supersaturation, yielding a range of morphologies and particles sizes. The second aim of the thesis was to prepare a novel range of three-dimensional photonic band gap materials composed of conventional phosphor materials.

This study documents the magmatic, hydrothermal and supergene mineralogy and geochemistry of phosphorus and rare earth elements in carbonatite complexes using examples from Tundulu (Malawi), Sokli (Finland), Siilinjarvi (Finland) and Kaluwe (Zambia). In carbonatites, phosphorus averages 1-2% P20S and forms the minerals fluorapatite and monazite. Hydrothermal and supergene processes enrich fluorapatite in Na and REEs through vitusite-type exchanges which lead to formation of vitusite, belovite and britholite; and in CO2 through anti-francolite substitutions. The highest rare earth element contents are found in late-stage ankerite carbonatites or similar rocks of low temperature origin (T < S(XtC) and in hydrothermally altered rocks, where they occur mainly as fluorocarbonates or carbonates. Such minerals are consistent with the REEs having been transported in form of mixed fluoride-carbonate complexes. The mineral paragenesis in hydrothermal veins suggests that different fluorocarbonates precipitated depending on the activity of Ca supplied to the fluid by the wall rocks. The various minerals are modelled to form by simple combinations of calcite (CaCO:v and bastnaesite (REEC03F) molecules. A secondary characteristic feature of these reactions is that extreme heavy rare earth enrichment occurs if the wall rocks are apatite-rich. Petrogenetic modelling using REEs suggests that carbonatites are unlikely to be derived from carbonated silicate magmas by fractional crystallisation or liquid immiscibility. These findings are supported by ex solution temperatures of about 9S0·C recorded using the calcitedolomite geothermometer for quenched lapilli from the Kaluwe carbonatite.

Les luminaires à LEDs représentent une alternative "verte" aux lampes fluorescentes et aux lampes à incandescence en répondant notamment à des critères de préservation de l'environnement : réduction de la consommation d’énergie, technologies sans mercure ni plomb et recyclables à 98%. Cependant, ces luminophores, qui sont actuellement utilisés dans les luminaires à LEDs, contiennent aujourd’hui des éléments de terres rares qui sont issus à 95% de Chine, créant de ce fait une situation de quasi-monopole et un risque réel pour le déploiement de la technologie LED dans les années à venir. Dans le cadre de cette thèse, nous nous sommes intéressés au développement de luminophores sans terres rares pour produire de la lumière blanche dans les luminaires à LEDs. Au cours de ces travaux nous avons étudié trois types de luminophores sans terres rares: luminophores organiques, luminophores hybrides (organiques-inorganiques) et quantum dots (QDs) type cœur-coquille. Les études optiques réalisées sur ces luminophores sous excitation LEDs UV ou bleue nous ont permis de déterminer leurs caractéristiques colorimétriques (IRC, T(K), PLQY(%)) et de mettre en évidence l’évolution de leurs performances dans les conditions d’usage. Pour obtenir une lumière la plus proche du blanc idéal, les luminophores les plus performants ont été sélectionnés puis mélangés en proportion adéquate avec une matrice polymère de type silicone pour conduire à un film composite offrant une émission blanche de qualité sous excitation LEDs UV ou bleue. Un autre volet de ce travail a été dédié à l’étude de la stabilité de ces luminophores (films ou poudres) en fonction du temps et de la température. L’influence de ces paramètres sur les propriétés optiques a été déterminée. Des performances optiques de 30% ont été enregistrées avec des caractéristiques photométriques intéressantes. Aussi, l’ensemble des résultats obtenus montre l’intérêt de poursuivre ces études sur les luminophores sans terres rares qui offrent des propriétés optiques intéressantes. Même s'ils ne concurrencent pas encore les luminophores inorganiques pour l’application « éclairage grand public », les luminophores sans terres rares peuvent déjà se positionner sur d’autres secteurs d’activité comme par exemple : l’éclairage d’ambiance, la signalétique le marquage anti-contrefaçons
Lighting technologies based on light-emitting diodes have become an alternative solution over the obsolete technologies (fluorescent lamps and incandescent lamps) due to their positive key criteria of environmental conservation: reduction of energy consumption and mercury/lead-free with 98% recycling technologies. However, the rare-earth elements, which are currently used in LED lightings, are produced by China at about 95%, thereby creating a monopoly situation on the rare-earth elements’ market and also a risk to the deployment of LED technologies in coming years. In this work, we have been interested in the development of rare-earth-free luminescent materials for LED lighting applications in order to produce a white light emission. Three kinds of rare-earth-free luminescent materials have been investigated: organic phosphors, hybrid (organic-inorganic) phosphors and core-shell quantum dots (QDs). The optical studies of these phosphors recorded upon UV and/or blue excitations allow us to determine their colorimetric parameters (CRI, T(K), PLQY(%)) and to demonstrate their optical performances for use in lighting devices. In order to yield a color emission close to ideal white light, the best phosphors were selected and then introduced by mixing them in appropriate proportions into silicone polymers. Another part of this work was devoted to the studies of stability of phosphors (films or powders) under operating conditions of LEDs, moreover, variation of their optical properties as a function of time and temperature were also determined. The optical performances about 30% have been recorded with some interesting colorimetric parameters. Although these materials have presented lower photoluminescence properties compared with commercial rare-earth based inorganic phosphors for “public lighting” applications, they can already be positioned on other luminescent sectors such as indoor lighting, signage anti-counterfeit marking

Існує необхідність в оптимізації і підвищенні ефективності існуючих процесів селективного біовилуговування фосфогіпсу, для розробки комплексного технологічного рішення, спрямованого на зниження негативного впливу фосфогіпсових відвалів на навколишнє середовище і повноцінного використання компонентів фосфогіпсу у виробництві як вторинного ресурсу.

碩士
國立交通大學
應用化學系碩博士班
99
In an attempt to investigate phosphors for light emitting diode (LED) application, we have successfully synthesized four series of thiogallate and oxythiogallate phosphors with compositions of SrLaGa3S6O:Ln (Ln = Ce3+, Eu2+, Ce3+/Li+ or Ce3+/Eu2+), (Sr1-xAx)LaGa3S6O:Ce3+ (A = Ca, Ba), Ca(La1-yMy)Ga3S6O:Ce3+ (or Eu2+) with M = Y, Gd,, and Sr2Ga2S5:Ce3+, respectively, by solid-state method under reduction atmosphere of H2S/Ar. .The crystal structure, luminescence, chromaticity and thermal luminescence quenching properties have been characterized by using X-ray diffraction (XRD), diffuse reflectance, and fluorescence spectroscopy. We first investigated the optimization of synthetic conditions of all phosphors and carried out phase identification using XRD. We then investigated luminescence spectra of thiogallate and oxythiogallate and found that both can be excited in the range of 300-450 nm with optimal excitation at 397 nm (Ce3+-activated phases) and 405 nm (Eu2+-activated phases), respectively. The effect of crystal field strength on the luminescence of the (Sr1-xAx)LaGa3S6O:Ce3+ (A = Ca, Ba) and Ca(La1-yMy)Ga3S6O:Ce3+ (M = Y, Gd) systems has also been studied by cation substitution for Sr2+ and La3+, respectively. The energy transfer from Ce3+ to Eu2+ in SrLaGa3S6O:Ce3+,Eu2+ was investigated and found to occur via a resonance-type dipole-dipole mechanism. The chromaticity coordinates of SrLaGa3S6O:5%Ce3+,xEu2+was observed to shift from blue to yellowish-green with x increasing from to 0.10. Furthermore, the charge compensation study revealed that the emission spectrum of charge-compensated SrLaGa3S6O:Ce3+,Li+ red-shifted as compared to that of the uncompensated (Sr1-nCen)LaGa3S6O phase. Finally, we have studied the temperature-dependent luminescence intensity for the SrLaGa3S6O:Ln (Ln = Ce3+, Eu2+) and Sr2Ga2S5:Ce3+ phosphors and discovered that the thermal quenching was observed to be more serious in Sr2Ga2S5:Ce3+ than that observed in SrLaGa3S6O:Ln.

博士
國立臺灣大學
化學研究所
100
The applications of phosphors according to different excitation sources are versatile due to the utilization of rare earth ions. The tunable energy levels of 5d orbital and the large number of energy levels of 4f orbitals can emit photons with different wavelength. In this thesis, excitation sources from vacuum ultraviolet (VUV), ultraviolet (UV) to visible photons, and electrons are investigated. Emission ranges from UV to visible range and near-infrared (NIR) are also utilized. The third chapter focuses on the synthesis of red-emitting oxynitride phosphor. Intraconfigurational 4f → 4f transitions are designed because of the determined environment for 5d → 4f transitions. The high thermal stability reveals that β–SiAlON is a good candidate for white light-emitting diodes (wLEDs) and plasma display panels (PDP). Pr3+ ions show the possibility of an alternative for red emitting activators. In the fourth chapter, comparison of LED- and FED-used phosphors under electron bombardment is made and it suggests a new class of host lattice should be developed. Evidences from solid-state nuclear magnetic resonance (ssNMR) lead to a different explanation of the incorporation of rare-earth ions into AlN host lattice. A new phosphor composition of AlN doped with Si4+ and Ce3+ ions is synthesized and shows the validity for field emission displays. The fifth chapter includes two proposed quantum cutting (QC) rare-earth combination for enhancing the efficiency of crystalline silicon (c-Si)-based solar cells: (1) adding a sensitizer to transfer the excited energy to the donor with 4f → 4f transitions , and (2) using a broad band donor such as Eu2+ and Ce3+ ions. It is concluded that due to the high energy of phonons required for Ce3+ ions, Eu2+-Yb3+ pairs is a better choice.

碩士
國立交通大學
平面顯示技術碩士學位學程
105
In this study, we successfully prepared the novel fluorescent materials and discussed their synthesis methods, luminescence properties and luminescent mechanism to apply to white light emitting diodes. The high temperature solid state method was used to synthesize the new phosphors, Ca2Y8Si6O26:Sm3+, La5BSi2O13:Sm3+, and BaY2Si3O10:Sm3+ with different calcination temperature. The X-ray diffraction, Electron microscopy, fluorescence spectrometer, temperature analyzer, chromaticity coordinates were used to analyze the crystal structure parameters, surface morphology, luminescent properties, fabrication performance, thermal stability and so on. The rare earth ions Sm3+ belong to the f-f forbidden transition, and the experimental results showed that there were multiple absorption narrow peaks appear ranged from 300 nm to 500 nm, which covered with the ultraviolet light and blue chip package. The strongest emission peak of Ca2Y8Si6O26:Sm3+ is locating at 648 nm, the strongest emission peak of BaY2Si3O10:Sm3+ is centered at 602 nm, and the strongest emission peak of La5BSi2O13:Sm3+ is near to 602 nm, and the phosphors are shot out of orange light. In this paper, the red light phosphors were packaged with BaMgAl10O17:Eu2+ blue commercial phosphor and (Ba, Sr)2SiO4:Eu2+ respectively with current red-emitting phosphors with a 390 nm wavelength N-UV light to investigate its luminescent properties.

碩士
明新科技大學
化學工程與材料科技系碩士班
107
The main lattice material of this study is carbonate，Doping the activation centers: Tb3+, Gd3+, Ce3+, respectively, to prepare red, green, and blue primary color phosphors，The synthesis method is a wet method in a solid-phase synthesis method， and is heated to 900℃and 1400℃at a temperature increase rate of 10℃per minute in a high-temperature furnace, and the calcination is carried out for 10 hours while the calcination is completed. The phosphor powder is finished and tested. The crystal structure is detected by X-ray diffraction (XRD), and the excitation and emission spectra of the phosphor are detected by photoluminescence (PL). Enter the CIE chromaticity coordinate map to know the exact color of the sample. 1.Sr2SiO4 series The sample with added Ce3+ ions has nonlinear optical blue light, and the sample with Tb3+ ions emits green light, while the addition of two rare piles of the earth (Ce3+, Tb3+) emits blue light and also has the characteristics of the above two samples. 2.Ba2SiO4 series The sample with Ce3+ ion added and calcined at 1400 °C has a nonlinear optical blue light. The sample with Tb3+ ion and calcined at 1400 °C emits green light while adding two rare piles of the earth (Ce3+, Tb3+) to emit blue light. With the characteristics of the above two samples, the same calcination temperature is also visible at 1400 °C. 3.Ca2SiO4 series When the calcination temperature is 1400 °C, the luminescence efficiency and crystallinity are better. The sample with Ce3+ has nonlinear optics and emits blue light; the sample with Tb3+ emits green light; while the sample with Ce3+ and Tb3+ remains at the same time. The characteristics of the aforementioned samples showed that the sample to which Gd3+ was added emitted red light.

碩士
國立成功大學
電機工程學系碩博士班
96
Rare earth-activated YVO4 phosphors have been attracting more attention in recent years because of their high luminescent intensities and stability under UV or UVU excitation as comparison with the conventional phosphors. Thus, rare earth-activated YVO4 phosphors have been considered as one possible luminescent material for flat display devices, such as plasma display panel (PDP) and field emission displays (FED). In this thesis, we have employed solid state reaction method and successfully prepared Tm- and Dy-codoped YVO4 with high luminance of white light emission. The relationship between the ratio of Tm3+/Dy3+ and the chromaticity is also studied. The best white-light emission was observed with YVO4：0.01mol(Tm0.2Dy0.8). Since the energy is efficiently transferred from VO43- to the two dopants Tm3+ and Dy3+, YVO4：0.01mol(Tm0.2Dy0.8) exhibits a strong white light emission. Additionally, we have investigated the morphological crystal structure and luminescent properties of YVO4：0.01mol(Tm0.2Dy0.8) thin film phosphors deposited by RF magnetron sputtering deposition. In particular, the effects of pressure, power and annealing temperature on luminescent properties of YVO4：0.01mol(Tm0.2Dy0.8) thin film phosphors have been examined. We concluded that the best white-light emission is achieved under the following conditions： pure Ar atmosphere, pressure of 5mtorr, RF power of 200W, substrate temperature of 350℃ and annealing temperature of 800℃.

碩士
國立成功大學
材料科學及工程學系碩博士班
98
Rare-earth (RE) ion doped phosphors, Li3Ba2La3-xREx(MoO4)8 (RE = Eu3+, Dy3+), were synthesized by a solid-state reaction process at 800C. The structural and photoluminescent properties of the prepared phosphors were investigated by X-ray diffraction, scanning electron microscopy, Raman scatter spectroscopy, UV-visible absorption, and photoluminescence (PL) spectroscopy. The aim of the research was to develop novel phosphors for the UV-LED to white light conversions. The experimental results showed that the dominant emissions of the Li3Ba2La3-xEux(MoO4)8 phosphors under the UV excitation (394 nm) were at 593 nm and 618 nm, originating from the electronic transitions between the trivalent RE states. Due to the high phonon frequency of the host lattice, the transitions from the emitting levels higher than 5D0 were not observed in the PL spectra. The above two observed emissions were due to the 5D0-＞7F1 (593 nm) and 5D0-＞7F2 (618 nm) transitions. In particular, the 5D0-＞7F2 emission was very strong and for the x=2.1 samples, its peak intensity was about 3.3 times more than the commercial phosphors ZnS:(Mn2+,Te2+). The CIE chromaticity coordinate of the Li3Ba2La0.9Eu2.1(MoO4)8 red emissions was calculated to be at (0.67, 0.33), which is almost the same as the standard red chromaticity of the NTSC system. In the Li3Ba2La3-xDyx(MoO4)8 (x=0.01-0.24) series, the dominant emissions under the UV excitation (388 nm) were from the 4F9/2-＞6H15/2 (blue) and 4F9/2-＞6H13/2 (yellow) transitions, and the intensity of the later was stronger. The mixture of all the emissions had the CIE chromaticity coordinates at (0.35, 0.40), which is at the yellowish-white color region.

碩士
國立交通大學
應用化學系碩博士班
101
White LEDs fabricated with blue or near-UV LED chips and compatible R/G/B phosphors is the main stream of current solid-state lighting device. This research is attempted to develop new fluorosulfide and oxyfluorosulfide phosphors undisclosed in the literature or patent application. We have prepared four series phosphors with compositions of CeSF:Lnn+ (Lnn+ = Gd3+, Y3+, Tb3+, Mn2+), La3OF3S2:Ce3+, Ce2CaF4S2:Tb3+ and (Ce1-xYx)2SrF4S2 by solid-state reactions in evacuated sealed quartz glass tubes at 900-1000℃, which were further characterized by powder X-ray diffraction, fluorescence spectroscopy, and electron microscopy to investigate their phase identity, luminescence, microstructures, chromaticity, quantum efficiency and thermal luminescence quenching behaviors. Based on the characterization results, we then evaluated their potential applications in fabrication of white light LEDs. This thesis first investigates the optimization of synthesis conditions and performs X-Ray diffraction characterization and phase identifications. The second part deals with the luminescence of La3OF3S2:Ce3+ and the third part investigates the luminescence of Mn2+-doped fluorosulfide and oxyfluorosulfide phosphors. Fourthly, this research investigates the luminescence of Ce3+/Tb3+-codoped fluorosulfides and studies the possibility of Ce3+ → Tb3+ energy transfer. Finally, we investigated the thermal luminescence quenching property of all synthesized phosphors and fabricated a white-light LED device using Ce2CaF4S2:Tb3+ and blue-emitting commodity phosphors in combination of a 365 nm near-UV LED chip.

碩士
國立成功大學
奈米科技暨微系統工程研究所
97
In this thesis, the (Ca, IIA)3(VO4)2: Eu3+ (IIA=Mg, Sr, Ba) red phosphors were prepared by the solid-state reaction method for the first time, and the preferable sintered condition was obtained at 1050 oC for 6 h. To improve the luminescence intensity of Ca2.82(VO4)2: 0.12Eu3+, an attempt was made to replace Ca2+ by (IIA)2+. It was found either of IIA substitution enhanced the PL intensity of Ca2.82(VO4)2: 0.12Eu3+ at different (IIA)2+ contents under 465 nm excitation. According to the changes of the lattice constants, this enhancement may originate from the lower site symmetry of the Eu3+ ion in the center with noninversion symmetry. It was noted Ba2+ was the best choice of (IIA)2+ ions (IIA=Mg, Sr, Ba) in partial substitution for Ca2+ to enhance the PL intensity. And the optimum value of the Ba2+ content (y) was at 9.9 mol% in (Ca1-yBay)2.82(VO4)2: 0.12Eu3+. The (Ca0.901Ba0.099)2.82(VO4)2: 0.12Eu3+ phosphor showed 136% improved integrated intensity than that of the Ca2.82(VO4)2: 0.12Eu3+ phosphor. Compared to commercial oxysulfide and sulfide red phosphors suitable for blue excitation, our synthesized phosphor (Ca, Ba)3(VO4)2: Eu3+ has the advantages of no chemical instability and sulfur pollution. The luminescence intensity of (Ca0.901Ba0.099)2.82(VO4)2: 0.12Eu3+ phosphor has been successfully further enhanced by adding the sensitizer, Sm3+ ion. We have discovered the energy transfer from Sm3+ to Eu3+ through the relative decline and growth in emission peaks of Sm3+ and Eu3+, respectively, as well as the variation of the decay behaviors of the Sm3+ 4G5/2→6H9/2 transition with the increasing Eu3+ content. The mechanism of the energy transfer from Sm3+ to Eu3+ was investigated and determined as the dipole-quadrupole interaction. The energy transfer efficiency, probability and the critical concentration in our Sm3+→Eu3+ system were also estimated. The optimized red phosphor (Ca0.89Ba0.099)2.82(VO4)2: 0.02Sm3+, 0.12Eu3+ is well-excited by the 465 nm blue lights, so it gives a potential for this phosphor to be applied on the phosphor-converted white LED with a blue chip (450-470 nm). Besides, the good overlap of the PLE and PL spectrum of (Ca0.89Ba0.099)2.82(VO4)2: 0.02Sm3+, 0.12Eu3+ phosphor and the absorption spectrum of CuPc indicates the potential use of the down-conversion phosphor coating to increase the performances of CuPc-based solar cells. We also synthesized the new infrared Ca3(VO4)2: Yb3+ phosphors suitable for UV excitation. The infrared emission peak at 983 nm under excitation of 310 nm was observed and the optimum Yb3+ content was 14 mol%. And the sufficiently large SR’s variation (~0.6 A/W) of a poly-Si solar cell for this phosphor indicates this phosphor can be used as a potential candidate to increase the power conversion efficiency of poly-Si solar cells.

碩士
國立交通大學
應用化學系分子科學碩博士班
100
Fluorosulfide and oxyfluorosulfide-based phosphors have relatively low synthetic temperature and appropriate excitation wavelengths for applications in fabricating white-light LEDs. To enhance the thermal stability of sulfides, we choose the fluorosulfides and oxyfluorosulfide as host matrices and activated with Ce3+ and Eu2+ as activator, respectively. In this study, we have prepared five series of fluorosulfide and oxyfluorosulfide phosphors, viz., Y3S2OF3:Ce3+, La2MF4S2:Ce3+ and La2MF4S2:Eu2+(M = Ca, Sr) using sealed quartz tube at 850-1000℃and 1150℃, respectively. These phosphors can be excited by radiation with wavelength ranging from 300 nm to 500 nm and their emission colors almost cover the whole visible spectral range. The content of this thesis can be divided into two parts. Firstly, we will introduce the background knowledge of phosphors used in LEDs, and then elaborate the design rules, the motivations and goals of the study. The synthetic methods and further characterization results will be discussed in the second part.

碩士
國立成功大學
材料科學及工程學系碩博士班
97
The objet of this study is to synthesize Li3Ba2Gd3(MoO4)8 doped with various activators(Eu3+,Tb3+,Dy3+,Er3+,Sm3+), and the raw material had been mechanically activated by grinding in high energy vibromill followed by calcined at temperature of 900℃ for 12 h. By using XRD, SEM, PL spectra, and UV-visable spectra, the characterization of structure, morphology of powders and photo-luminescent properties of phosphors were analized. The dominant emission peaks of Li3Ba2Gd3(MoO4)8:Eu3+ phosphor are 5D0→7F1(591nm)、5D0 →7F2(614nm) which are originate from intra-4f transitions of excited state. The intensity of the emission from 5D0 to 7F2 is stronger than 5D0 to 7F1 and three times more than commercial phosphors, ZnS:Mn2+,Te2+ when Eu3+ concentration in x=2.4. The CIE chromaticity coordinates of red emission of the Li3Ba2Gd0.6Eu2.4(MoO4)8 phosphor is (0.67, 0.33) which is just at NTSC system standard red chromaticity. There are two regions in the excitation spectra of Li3Ba2Gd2 Tb1(MoO4)8 phosphor；one is assigned from 4f��5d transition in 200 to 300 nm, and the others are from intra-4f transitions in 350 to 500 nm. The dominant emission peak of Li3Ba2Gd2Tb1(MoO4)8 phosphor is 5D4��7F5 under excitation of 307nm. The CIE chromaticity coordinates of green emission of the Li3Ba2Gd2 Tb1(MoO4)8 phosphor is (0.25, 0.58). The the other series of green phosphor is Li3Ba2Gd2.95Er0.05(MoO4)8.Because its emission peaks locates in the light of green region, it has better color rendering index than Li3Ba2Gd2 Tb1(MoO4)8. However, the valence electrons are shielded by the 5s and 5p outer electrons, the valance electrons of trivalent rare earth ions are weakly affected by ligand ions in crystals, so the features of optical spectra of the most phosphors doped with trivalent rare earth, such as Li3Ba2Gd3(MoO4)8:Dy3+ and Li3Ba2Gd3(MoO4)8:Sm3+ is similar to those expected for free ions.

博士
國立交通大學
應用化學系碩博士班
105
The thesis is divided into three parts. Firstly, the study of the blue LED-excitable cyan-emitting, green-emitting, and reddish orange-emitting thiosilicate phosphors. Secondly, the study of the blue LED-excitable cyan-emitting and reddish orange-emitting halothiosilicate phosphors. Finally, the study of the near-UV LED excitable cyan-emitting and green-emitting thiogallates. In Chapter 1, the research background and current status of sulfides and thiosilicates are introduced, and the motivations and goals of this thesis are elaborated. The literature review was focused on the fundamentals of phosphors, concentration quenching of activators, and mechanism of energy transfer of different types of phosphors. In Chapter 2, we describe the synthesis and characterization methods of the thiosilicate phosphors; BaLa2Si2S8:R (R = Ce3+ or Eu2+), CaY2Si2S8:Ce3+, La3Br(SiS4)2:R (R = Ce3+ or Eu2+), BaGa2SiS6:Eu2+, and Ba2Ga8SiS16:Eu2+. In Chapter 3, we discuss the crystal structure and spectroscopic properties of the BaLa2Si2S8:R (R = Ce3+, Eu2+), CaY2Si2S8:Ce3+, La3Br(SiS4)2:R’ (R’ = Ce3+ or Eu2+), BaGa2SiS6:Eu2+, and Ba2Ga8SiS16:Eu2+ phosphors and their LED lighting applications. In Chapter 4, the properties of the thiosilicate phosphors are summarized and the future work is discussed.

碩士
國立臺南大學
材料科學系碩士班
107
In this study, solid state reactions were performed to synthesize a series of lithium yttrium molybdate phosphors, i.e., 1) those co-doped by samarium (Sm) and europium (Eu), 2) those doped by either Sm or Eu, and 3) those not doped. The crystal structure, luminous characteristics, and surface structure of the above- mentioned phosphors were analyzed by means of X-ray diffractometers (XRD), photoluminescence (PL) spectrometers, and scanning electron microscopes (SEM) respectively. XRD analysis shows that both lithium yttrium molybdate phosphors and sodium yttrium molybdate phosphors belong to tetragonal scheelite-type crystallines, and that potassium yttrium molybdate phosphors belong to orthorhombic crystallines. As shown by the PL spectrums, LiY0.96(MoO4)2:4Sm has a strong absorption peak at 407 nm and a dark red emission at 651 nm; in addition, the sintering temperature maintained at 900 °C for 5 hours has the optimal luminous intensity. LiY0.91(MoO4)2:9Eu has two strong absorption peaks at 396 nm and 466 nm, with a strong red emission at 619 nm. Moreover, the sintering temperature maintained at 900 °C for 5 hours has the optimal luminous intensity. Lithium yttrium molybdate phosphors codoped by Sm and Eu display strong absorption peaks at 396 nm, 407 nm and 466 nm, with a strong red emission at 619 nm. Besides, the absorption peak at 466 nm is about two times as high as that at 396 nm. Excited at 466 nm and sintered at 900 °C for 5 hours, LiY0.87(MoO4)2:4Sm, 9Eu shows the optimal luminous intensity. After displacement of Na or K ion, LiY(MoO4)2 excited at 466 nm still has the optimal luminous intensity. SEM analysis shows that, whether doped by one rare earth element or codoped by two rare earth elements, all the phosphors exhibit irregular polyhedral grains and agglomeration. Meanwhile, the phenomenon of agglomeration tends to increase the luminous intensity of red-light phosphors.

碩士
國立交通大學
應用化學系碩博士班
102
With the gradual enhancement of environmental awareness, the development of green luminescent materials has been an important issue in phosphors research. This research is attempted to synthesize and investigate new UV-emitting materials, which can be excitated by 172 nm and used for the applications of phototherapy, sterilization, and disinfection. We have explored and investigated the luminescence mechanism of four series of UV-emitting phosphors, including nine types of rare earth-doped phosphates, silicates and borates. In this study, using the vacuum ultraviolet (VUV) light source provided by National Synchrotron Radiation Research Center (NSRRC), as well as the X-ray diffraction technique and electron microscopy analysis, we have prepared and investigated UVB-emitting NaCa(Y,Gd) (PO4)2, Na2(Y,Gd)2O(BO3)2, Li6(Y,Gd)(BO3)3, Na(Y,Gd)Si2O6, NaCa (Y,Pr,Gd)(PO4)2, Li6(Y,Pr,Gd)(BO3)3 and Na(Y,Pr,Gd)Si2O6; UVC- emitting NaCa(Y,Pr)(PO4)2 and Na(Y,Pr)Si2O6. Under excitation at 172 nm, the NaCa(Y,Gd)(PO4)2, Na2(Y,Gd)2O(BO3)2, Li6(Y,Gd)(BO3)3, Na(Y,Gd)Si2O6, NaCa(Y,Pr,Gd) (PO4)2, Li6(Y,Pr,Gd)(BO3)3 and Na(Y,Pr,Gd)Si2O6 phosphors were found to give sharp UVB emission centered at 313 nm, which was attributed to the 4f7→4f7 transition of Gd3+. Under the same excitation, NaCa(Y,Pr)(PO4)2 and Na(Y,Pr)Si2O6 were found to emit UVC light, which was found to be due to the 4f15d1 →4f 2 transition of Pr3+. With the co-doping of Pr3+ as a sensitizer, NaCa(Y,Pr,Gd)(PO4)2, Li6(Y,Pr,Gd)(BO3)3, and Na(Y,Pr,Gd) Si2O6 exhibit a much stronger emission at 313 nm. The emission intensity of the UVB-emitting NaCa(Y0.8293Pr0.0007Gd0.17)(PO4)2, Li6(Y0.695Pr0.005 Gd0.3)(BO3)3 and Na(Y0.775Pr0.005 Gd0.22)Si2O6 was found to be 1.6, 5.4, and 1.4 times that of the UVB emission of the patented LaB3O6:Bi3+,Gd3+ commodity, respectively. Our investigation results indicate that the above three Pr3+/Gd3+-coactivated phosphors may have great potential for practical application in phototherapy and tanning. The luminescence performance of all types of UV radiation was found to be crucially dependent on the chemical compositions, bonding and crystal structure of the host matrix.

碩士
國立交通大學
應用化學系碩博士班
100
In this study, we have successfully synthesized several novel phosphors with compositions of Ca2(Ba1-xEux)3(PO4)3F, (Ca1-xEux)4Si2O7F2, Ca2(Ba1-2x- CexLix)3(PO4)3F, (Ca1-xCex)4Si2O7F2, Ca2(Ba0.99-yCe0.005Li0.005Euy)3(PO4)3F, and (Ca0.998-yCe0.002Euy)4Si2O7F2 by using solid-state method under reducing H2/Ar atmosphere. The crystal structure, luminescence and chromaticity properties of these phosphors were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DR), and photoluminescence spectroscopy. This thesis first reports the optimization of synthetic condition for all phosphors and the analysis of XRD profiles. Then, the spectroscopic properties and thermal-quenching behaviors of Eu2+-doped phosphors were investigated, which were then rationalized by considering nephelauxetic effect and crystal field strength. Furthermore, the luminescence properties and thermal- quenching behaviors of Ce3+-activated phosphors have also been investigated. On the other hand, the Ce3+→Eu2+ energy transfer in systems of Ca2Ba3(PO4)3F: Ce3+, Li+, Eu2+ and Ca4Si2O7F2: Ce3+, Eu2+ were also studied and the energy transfer mechanisms were determined to be the dipole-dipole type interactions. Finally, this thesis discusses the results of all phosphors that we have synthesized and evaluates its applicability in the fabrication of white-LEDs.

碩士
國立交通大學
應用化學系碩博士班
108
In this study, solid-state synthesis was successfully used to prepare nine novel Ce3+ and Eu2+-activated rare earth thiosilicate and halothiosilicate phosphors such as La3X(SiS4)2:Eu2+(X = Cl, I), Y9Al5S21:Ce3+, Ba3AlS4Cl:Eu2+, Y6Al2SiS14:Ce3+, AM(SiS4):Ce3+ (A = K, Cs; M = La, Y), the excitation mainly locates in the near- ultraviolet to the blue region (350 nm-460 nm), the emission locates in the region of blue-green to orange. Our research results provide new choices of phosphors for application in fabrication of white light-emitting diodes (WLEDs). The above-mentioned phosphors were characterized by X-ray diffraction (XRD) and fluorescence spectroscopy to study the phase purity and optimal synthesis conditions and activator doping concentration. In particular, the crystal structure of CsY(SiS4) was determined by the single crystal XRD. Luminescence characterizations were performed to obtain diffuse reflectance spectra, variable temperature PL spectra, quantum efficiency measurement and chromaticity coordinates determination. The first part mainly introduces research background, phosphor design principle and motivations. The second chapter discusses the preparation methods and characteristics of the phosphors developed. The third chapter details the crystal structure and luminescence properties of all phosphors. The fourth chapter summarizes the characteristics of the phosphors for WLEDs fabrication developed in this research and finally discusses the work that can be continued in the future.

In this work, alkaline earth aluminate phosphors doped with rare-earth ions and manganese were synthesized using combustion method. Several characterization techniques were used to study the structural and luminescent properties of the as-synthesized phosphors, namely X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray energy Dispersive Spectroscopy (EDS), Ultraviolet-Visible (UV-Vis) Spectroscopy, Photoluminescence (PL), and Thermoluminescence (TL). The structural properties were studied by collecting the XRD patterns of the samples using an X'Pert PRO PANalytical diffractometer with CuKα at λ = 0.15405 nm. The particle morphologies of the as-synthesized powder phosphors were investigated using a JEOL JSM-7500F field-emission scanning electron microscope (FE-SEM). The optical properties of the phosphors were studied using Perkin-Elmer Lambda 750s UV-Vis spectrometer, Jobin Yvon/SPEX FluoroLog spectrofluorometer (Model FL-1040) and Riso TL/OSL reader (Model DA-20). The as-prepared SrAl2O4:Eu 2+ ; SrAl2O4:Dy 3+; SrAl2O4:Mn 2+; phosphors were synthesized at an initiating temperature of 600 oC. The XRD patterns were consistent with the low temperature monoclinic structure of SrAl2O4 for all the as-synthesized phosphor powders. SEM measurements showed nano-rod like particles. The SrAl2O4:Eu 2+ ; SrAl2O4:Dy 3+; SrAl2O4:Mn 2+ samples were excited using a 450 W Xenon light source at 364 nm, 390 nm, and 426 nm respectively. A broad blue emission peak at 500 nm shown by the SrAl2O4:Eu 2+ sample is attributed to the 6 1 7 4f 5d 4f transition of the Eu 2+ ion. Also, the red sharp emission lines due to the 4f-4f transition of the Eu 3+ were observed. SrAl2O4:Dy3+ samples exhibited blue, green, and red emissions which can be atributed to the 4 6 9/2 15/2 F  H ,4 6 9/2 13/2 F  H , and 4 6 9 11 2 2 F  H transitions of Dy 3+ ions respectively. The two broad emissions (green at 513 nm and red at 650 nm) shown by 2+ 0.98 2 4 0.02 Sr Al O :Mn sample can be atributed to the 4 4 6 6 1 1 T ( G)  A ( S) transition of the Mn 2+ ion in the sample. The SrAl2O4:Eu 2+ , Dy 3+ ; SrAl2O4:Eu 2+, Mn 2+ ; SrAl2O4:Dy 3+, Mn 2+; and SrAl2O4:Eu 2+ ,Mn 2+, Dy 3+ phosphors were synthesized by combustion method at an initiating temperature of 600 oC. The blue emissions were observed in all the samples except SrAl2O4:Eu 2+ ,Mn 2+, Dy 3+ sample. The SrAl2O4:Eu 2+ ,Mn 2+, Dy 3+ phosphor showed the longest afterglow intensity. The BaAl2O4 doped with Eu 2+ , Mn 2+ and Dy 3+ phosphors synthesized at an initiating temperature of 600 oC using combustion method. The XRD patterns confirmed the hexagonal structure of BaAl2O4 in all the as-synthesized samples. A broad blue emission of the BaAl2O4:Eu 2+ sample at 490 nm is attributed to the 6 1 7 4f 5d 4f transition of the Eu 2+ ion in the sample. A red emission peak observed at 611 nm is due to the 4f - 4f transition of un-reduced Eu 3+ ions during the combustion reaction. A blue emission at 482 nm, a green emission at 575 nm, and a red emission at 663 nm of the BaAl2O4:Dy 3+ sample can be associated with 4 6 9/2 15/2 F  H ,4 6 9/2 13/2 F  H , and 4 6 9 11 2 2 F  H transitions of the Dy 3+ ions respectively. The green emission peaks exhibited by BaAl2O4:Mn 2+ sample at 512 nm is due to the 4 4 6 6 1 1 T ( G)  A ( S) transitions of the Mn 2+ ions. Barium aluminate phosphors doped with different concentrations of Dy 3+ ion were synthesized by combustion method at an initiating temperature of 600 oC. The XRD patterns confirmed the hexagonal structure of BaAl2O4. The emission peaks observed at 482 nm, 575 nm, and 663 nm are due to4 6 9/2 15/2 F  H ,4 6 9/2 13/2 F  H and 4 6 9 11 2 2 F  H transitions of Dy 3+ ion respectively. The PL measurements also confirmed the quenching of luminescence at higher concentrations of the Dy 3+ ion. The UV-Vis measurements has confirmed the increase in the band-gap of the BaAl2O4 sample followed by a decrease and an increase again as doping concentration of the Dy 3+ increased. The X-ray diffraction patterns of the Ca0.97M0.3Al2O4:Eu 2+ , Dy 3+ (M = Ba, Mg, and Sr) powder samples prepared by combustion method confirms the monoclinic structure of CaAl2O4 in all samples. A broad emission peak at 490 nm for both Ba 2+ and Mg 2+ substituted samples and the one for Sr 2+ substituted sample at 485nm are attributed to the 6 1 7 4f 5d 4f transition of the Eu 2+ . The decay curves confirmed that the Mg 2+ substituted sample has a longer persistence (phosphorescence) than all the other samples.
Physics
M. Sc. (Physics)

博士
國立成功大學
電機工程學系碩博士班
101
Our previous work [J. Am. Ceram. Soc., 93, 138 (2010)] reported a red phosphor Ca2.82(VO4)2:0.12Eu3+ which was well-excited by 465-nm blue light and was therefore a candidate for application to the phosphor-converted WLED (pc-WLED) with a blue chip (450-470 nm). On the basis of Ca2.82(VO4)2:0.12Eu3+, we sought to develop down-shifting (DS) inorganic phosphors for use in pc-WLEDs by the commonly-used solid-state reaction method, which was the main purpose of the present research. We found that substitution of not only a larger ion like Ba2+ [J. Am. Ceram. Soc., 93, 138 (2010)] but also a smaller one like Mg2+ (this research) replacing no ＞ 14.9% Ca2+ ions could enhance the integrated DS emission intensity of red phosphor Ca3(VO4)2:0.12Eu3+, indicating that both lattice expansion and contraction could decrease the site symmetry of Eu3+ in Ca3(VO4)2:0.12Eu3+ phosphor. This finding is anticipated to improve the Eu3+ emission intensity of other Eu3+-doped phosphors. To further investigate Eu3+ up-conversion (UC) behaviors, Yb3+ ion was used as a sensitizer. Interestingly, the enhanced Eu3+ emission from 5D1,2,3 states under UC excitation was observed as compared to that under DC excitation. This phenomenon led to the variation in the emission color of the optimized (Ca0.742Mg0.067)2.82(VO4)2:0.36Yb3+,0.12Eu3+ phosphor from red to near warm white as the excitation mechanism changed from DS to UC. Additionally, it was found that substitution of 3% Sr2+ replacing Ca2+ enhanced the red emission intensity of Ca2.82(VO4)2:0.12Eu3+ by 14% under 465-nm excitation. The conventional methods to determine multipolar mechanisms responsible for the energy transfer between different ions (I0/I － C plot) and alike ions (log(C/I) － logC plot) supposed hypotheses of I0/I ≫ 1 and βCθ/3 ≫ 1, respectively, where I0 and I are the emission intensity of the energy donor in the absence and presence of the acceptor; C is the sum of both energy donor and acceptor contents; θ represents the type of multipolar interactions, and β is a constant for each interaction. Compared with the conventional methods, the modified methods for investigation of the multipolar energy transfer proposed in this research demonstrated more precise and valid results. Excluding the prerequisite of I0/I ≫ 1, the concentration-dependent dipole-dipole multipolar interactions for the Sm3+ → Eu3+ energy transfer were observed for the first time based on the fitting results of (I0/I － 1) － C plots. Additionally, the Harris model was found to be an alternative way to release us from the prerequisite of βCθ/3 ≫ 1 when fitting the I/C － C plot. And a dipole-dipole multipolar interaction of 3-body type was found to be responsible for the concentration quenching of Sm3+ emission around 951 nm in the (Ca0.97Sr0.03)3(VO4)2 host.

Luminescent materials can be found in a broad range of everyday applications. While in the seventies and eighties, the field of luminescent materials seemed to be fairly well covered, research in nineties has been revitalized both in industry and academia. Improvements over the last three decades have led to phosphor materials that operate close to their physical limits. It cannot be expected that properties such as quantum yield and spectral energy distribution will be significantly improved or that distinctly better materials will be found in the near future. Recently, there is a considerable research activity in the field of luminescent materials for lighting and displays to improve the chemical stability and to adopt the materials to the production technology. Ongoing miniaturization, lifetime improvement and spectral stability of fluorescent lamps on the one hand and brightness and contrast improvement in imaging systems on the other hand demand luminescent materials with very high stability that is invariable to operating conditions. All of the today's efficient lighting sources are based on either direct or indirect light emission from plasma discharges. During the pioneering stage, fluorescent lamp industries predominantly used mixtures of two photo luminescent materials: (Zn,Be)2SiO4.'Mn2+ having two emission maxima at 520 and 600 nm and MgW04 with 480 nm emission. The emission from these two phosphors covers the major portion of the visible spectrum. However, the compound (Zn,Be)2Si04 is hazardous to health because of its beryllium content. In 1942, Jenkins showed that Ca5(PO4)3(F,Cl):Sb,Mn was a very efficient emitter. The halophosphates emit both in the blue (Sb3+) as well as in the orange (Mn2+) spectral region, thus in addition yield white light. By carefully adjusting the ratio of Sb3+ and Mn2+ ion concentrations, a white light emitting phosphor was obtained with color temperatures ranging between 6500 and 2700K. However, the drawback of the halophosphate lamps is that it is impossible to have simultaneously high brightness and high color rendering; if the brightness is high (efficacy -80 lm W"1), the color rendering index (CRI) is of the order of 60, the CRI value can be improved up to 90, but then brightness decreases (-50 lm W"1). In 1974, another important breakthrough came in the form of compact fluorescent lamp, based on the trichromatic phosphor blend which resulted color rending values of 80-85 (color 80 lamps) at high efficiencies of 100 lm W"1. The fluorescent lamps with very high color rendering and efficiency can be obtained if three narrow band emitters with emission maxima at 450, 540 and 610 nm are employed. A typical trichromatic lamp phosphor blend comprises of (i) Sr5(PO4)3Cl:Eu2\ BaMgAl1()O,7:Eu2' as blue component, (ii) Ce0.67Tbo.33MgAl,,0,9, LaPO4,Le3\Tb3+ as green component and (iii)Y2C>3:Eiru as the red component. The color 80 lamps employ line emitters that generated light in discrete wavelength intervals. Colored objects that absorb outside these spectral regions appear with a slightly different body color when illuminated with these lamps rather than with a black body radiator such as the light bulb. For these purposes, color 90 or Deluxe lamps have been developed. The emission maximum of the blue phosphor can be shifted towards longer Wavelength by substituting BaMgAli0Oi7:Eu2+ with Sr4Ali4025:Eu2+. The red and green line emitters can be substituted by broad band emitters covering the whole spectral range. For this concept, (Ce,Gd,Tb)MgB5Oi0:Mn has been developed as a red emitter in which energy transfer from Ce3+ via Gd3+ to Mn2+ gives rise to an additional broad band at 630 nm. On the other hand, (Ba,Sr,Ca)2Si04:Eu has been developed as an alternative green-band emitter in which depending on the exact composition, the phosphor emits between 550 and 580 nm with a high quantum yield. Unfortunately, the host lattice is not stable in water, which prevents its deposition on the lamp bulb from aqueous suspensions and for environmental reasons more and more lamps producers use water as the suspending solvent in production instead of butyl acetate. Therefore, it is necessary to develop a new full color emitting phosphors, which has both thermal and chemical stability for application in luminescent lighting. The classical cathode ray tube (CRT) invented as the brown tube more than 100 years ago has developed into a remarkably mature product considering the complexity of its manufacturing process. Cathode rays are a beam of fast electrons, the accelerating voltage in a television picture tube is high (>10 kV). Basic requirements of display phosphors are stability (2000 hr operation) and emission color purity according to the standards set by the European Broadcasting Union (EBU). The blue and green phosphors are still the very cheep ZnS based materials, essentially the same ever since color-TV was introduced in fifties. On the other hand, (Zn,Cd)S, Ag+,C1" was originally used as the red phosphor however, the broad emission centered at 650 nm due to intrinsic donor-acceptor transition leads to rather low lumen equivalent as large fraction of the emission integral lies outside the eye sensitivity curve. For this and the environmental reasons, it has been replaced by the much more expensive Y2O2S:Eu with main emission lines at 612 and 628 nm. Recently, the big electronic companies are trying to enforce flat panel displays e.g. PDPs (plasma display panels) and FEDs (field emission displays). This is because of the fact that when compared to the CRT screen pigments, FED phosphors are required to operate at lower voltages and higher current densities. Although the voltages used in FEDs are only 0.1 to < 2 kV, the high-energy surface excitation on the phosphor particles causes degradation of sulfides, leaving the oxide hosts as the only favorable choice. The phosphor blends used are mixtures of SrTiO3:Pr3+ (red), Y2Si05:Tb (green) and Y2Si05:Ce (blue). However, the white light generation efficiency is very low (-5 lm W"1) and required improvement of phosphor efficacy because of its distinct advantages such as a very wide range of operational temperatures, stability under rugged conditions and wide viewing angle of emission. Similarly, in PDPs blue emitting BaMgAlioOniEu, green emitting Z^SiO^Mn and red emitting (Y,Gd)BO3:Eu are mostly used which shows a screen efficiency of about 1.5 lm W"1, just only half that of a CRT used in today's TV sets. However, the advantages of PDPs over CRTs are that it is not sensitive towards the display manufacturing process, which includes high temperature annealing up to about 600°C and it is stable under the harsh conditions of a Ne/Xe plasma used in PDPs (ion bombardment, VUV radiation). This puts pressure on the development of phosphor for maximum brightness and high stability to replace completely the classical CRTs. On the other hand, the invention of the blue-light emitting diode (LED) based on GaN can be regarded as a triumph of materials chemistry. In principle, it is possible to vary the emission wavelength of blue GaN-based LEDs between 370 nm (band-gap of pure GaN) and 470 nm by increasing the indium (In) content in InGaN devices. Assuming a conversion from the incident light by a phosphor material emitting at 555 nm, InGaN is coated with (Yi.xGdx)3(Ali-yGay)5Oi2:Ce (YAG:Ce) which has broad yellow band varying between 510 and 580 nm. This allows the adjustment of white color temperature from 8000 down to 3000 K. Recently, S^SiCU and S^SiOs have attracted current interest due to their potential applications in developing white light-emitting-diodes (LEDs) because GaN (400 nm chip)-coated with Sr2Si04:Eu2+ or Sr3SiC>5;Eu2+ exhibits better luminous efficiency than that of the industrially available product such as InGaN (460 nm chip)-coated with YAG:Ce. However, the major drawback of this combination is the strongly decreasing overall efficiency upon lowering the color temperature. This can be solved by using a phosphor material that has sufficient absorption at the emission wavelength of the blue diode, the quantum yield should be high under UV/Vis excitation and the FWHM of the emission band should be as small as possible in order to achieve high luminous output. The search for stable inorganic rare-earths phosphors with high absoiption in the near UV/blue spectral region is therefore an attractive research work. Since luminescence materials are a key component for lighting and display concept, research in the field of rare-earths doped oxide phosphors is carried out. Although state-of-the-art materials fulfill most requirements, improvements are still necessary to further boost the efficiency of the phosphor materials. Since it is not expected that materials will be found that perform better than the already established phosphor, the present work concentrates on the improvements of the phosphor by modifying the chemical and niicrostructurai features as well as the crystal structure. Chapter I gives a brief introduction to luminescence in solids, physical aspects and applications. Chapter II describes the synthesis and various experimental techniques employed in the investigation. Chapter III deals with photoluminescence and energy transfer involving charge transfer states in Sr2-xLnxCe04+x/2 (Ln = Eu and Sm) leading to an efficient full color emitting phosphor for luminescent lighting. Chapter IV and V describe charge transfer transition involving interface states associated with transitional nanophaseprecipitates leading to photoluminescence enhancement of SrTiO3:Pr3+,Al3+ and SrAli2Oi9:Pr3+,Ti4\ The light induced charge transfer leading to changing oxidation state of Eu in Sr2Si04 involving transient crystal structure results an efficient material for optical storage is presented in Chapter VI.Photoluminescence due to efficient energy transfer from Ce3+ to Tb3+ and Mn2t in SnAlioSi02o leading to an efficient phosphor for FEDs is presented in Chapter VII. Chapter VIII describes charge transfer transition involving trap states leading to long phosphorescence in SrAl2-xBxO4 (0