In order to confirm the relationship between the luminescence and the ratio of Ce3+/Ce4+ more clearly, a series of YAG:Ce3+ (Yttrium Aluminum Garnet, Y2.94Al5O12:0.06Ce3+) phosphors were pre- pared under different sin...In order to confirm the relationship between the luminescence and the ratio of Ce3+/Ce4+ more clearly, a series of YAG:Ce3+ (Yttrium Aluminum Garnet, Y2.94Al5O12:0.06Ce3+) phosphors were pre- pared under different sintering atmosphere. A semi-quantitative analysis based on X-ray photoe-lectron spectroscopy (XPS) was introduced to study the mole ratio of Ce3+/Ce4+ in the as-synthesized YAG:Ce3+ phosphors. The results indicated that the percentage of Ce3+/(Ce3+ + Ce4+) reached 88.46% under the reduction atmosphere. The emission intensity of YAG:Ce3+ phosphors was in-creased significantly with the increasing of Ce3+ concentration.展开更多
A Matlab （2009a） program was developed to simulate the photons emitted by the LED chips. The photons＇ transmission, reflection, and refraction in phosphor layers with different shapes were calculated in this progra...A Matlab （2009a） program was developed to simulate the photons emitted by the LED chips. The photons＇ transmission, reflection, and refraction in phosphor layers with different shapes were calculated in this program. The CCT was calculated at different emergent angles with different layer profiles, such as planar layer, hemispherical layer （with different diameters）, half ellipsoid layer and other irregular shapes. As a consequence of optimization of angular color uniformity, the trend of configuration of the phosphor layer was discussed and analyzed.展开更多
YAG： Ce^3 ＋ phosphor particles were prepared using polyacrylamide gel method. The structure evolution of powders during annealing process was followed by X-ray diffraction determination. It is found that some interm...YAG： Ce^3 ＋ phosphor particles were prepared using polyacrylamide gel method. The structure evolution of powders during annealing process was followed by X-ray diffraction determination. It is found that some intermediate phases, including θ-Al2O3, YAM and YAP, are formed when calcining polyacrylamide gel, however, the pure YAG phase can be formed directly when calcining polyacrylamide gel with α-Al2O3 as seed crystal. These facts show that the existence of α- Al2O3 seed crystal can block the formation of θ-Al2O3, YAM and YAP, and accelerate its reaction with Y2O3 to form YAG phase directly at lower temperature. The emission peak of prepared YAG ： Ce^3 ＋ phosphor is wide with maximum at 550 nm and the exitation band has two peaks, the major one is around at 460 nm, which matches the blue emission of GaN LED and is suitable for the assemble of white LED. Some fluxes can enhance the photoluminescence intensity of phosphor particles, that can be attributed both to the improvement of crystallization processes of YAG and to the stabilization of trivalence cerium ion in YAG：Ce^3 ＋.展开更多
YAG:Ce3+ phosphor was prepared by sol-gel low-temperature combustion method. The effects of the precursor properties and calcining temperature on the crystallization process, microscopic morphology and luminescent pro...YAG:Ce3+ phosphor was prepared by sol-gel low-temperature combustion method. The effects of the precursor properties and calcining temperature on the crystallization process, microscopic morphology and luminescent properties of phosphor were studied. The results indicate that the pure phase of YAG can be obtained at 800 ℃ by sol-gel low temperature combustion method, using citric acid as complexing agent. When the molar ratio of metal ion to citric acid is 2.0 and pH value is 2, the crystallinity increases and the phosphor particle size grows up gradually with the increase of the calcining temperature. The powders were characterized through thermal analysis, X-ray diffraction analysis and scanning electron microscope analysis. The excitation spectra of YAG:Ce3+ phosphor take on a double peak structure, and the peak value of the main excitation spectra occurs at 460 nm and that of the emission spectra is near 530 nm. With the gradual increase of the calcining temperature, the peak position of excitation and emission spectra remains basically unchanged, but its relative intensity increases gradually.展开更多
文摘In order to confirm the relationship between the luminescence and the ratio of Ce3+/Ce4+ more clearly, a series of YAG:Ce3+ (Yttrium Aluminum Garnet, Y2.94Al5O12:0.06Ce3+) phosphors were pre- pared under different sintering atmosphere. A semi-quantitative analysis based on X-ray photoe-lectron spectroscopy (XPS) was introduced to study the mole ratio of Ce3+/Ce4+ in the as-synthesized YAG:Ce3+ phosphors. The results indicated that the percentage of Ce3+/(Ce3+ + Ce4+) reached 88.46% under the reduction atmosphere. The emission intensity of YAG:Ce3+ phosphors was in-creased significantly with the increasing of Ce3+ concentration.
文摘A Matlab （2009a） program was developed to simulate the photons emitted by the LED chips. The photons＇ transmission, reflection, and refraction in phosphor layers with different shapes were calculated in this program. The CCT was calculated at different emergent angles with different layer profiles, such as planar layer, hemispherical layer （with different diameters）, half ellipsoid layer and other irregular shapes. As a consequence of optimization of angular color uniformity, the trend of configuration of the phosphor layer was discussed and analyzed.
文摘YAG： Ce^3 ＋ phosphor particles were prepared using polyacrylamide gel method. The structure evolution of powders during annealing process was followed by X-ray diffraction determination. It is found that some intermediate phases, including θ-Al2O3, YAM and YAP, are formed when calcining polyacrylamide gel, however, the pure YAG phase can be formed directly when calcining polyacrylamide gel with α-Al2O3 as seed crystal. These facts show that the existence of α- Al2O3 seed crystal can block the formation of θ-Al2O3, YAM and YAP, and accelerate its reaction with Y2O3 to form YAG phase directly at lower temperature. The emission peak of prepared YAG ： Ce^3 ＋ phosphor is wide with maximum at 550 nm and the exitation band has two peaks, the major one is around at 460 nm, which matches the blue emission of GaN LED and is suitable for the assemble of white LED. Some fluxes can enhance the photoluminescence intensity of phosphor particles, that can be attributed both to the improvement of crystallization processes of YAG and to the stabilization of trivalence cerium ion in YAG：Ce^3 ＋.
文摘YAG:Ce3+ phosphor was prepared by sol-gel low-temperature combustion method. The effects of the precursor properties and calcining temperature on the crystallization process, microscopic morphology and luminescent properties of phosphor were studied. The results indicate that the pure phase of YAG can be obtained at 800 ℃ by sol-gel low temperature combustion method, using citric acid as complexing agent. When the molar ratio of metal ion to citric acid is 2.0 and pH value is 2, the crystallinity increases and the phosphor particle size grows up gradually with the increase of the calcining temperature. The powders were characterized through thermal analysis, X-ray diffraction analysis and scanning electron microscope analysis. The excitation spectra of YAG:Ce3+ phosphor take on a double peak structure, and the peak value of the main excitation spectra occurs at 460 nm and that of the emission spectra is near 530 nm. With the gradual increase of the calcining temperature, the peak position of excitation and emission spectra remains basically unchanged, but its relative intensity increases gradually.
