Synthesis And Properties Of Yellow YAG Phosphors With High Efficiency And High Stability For White LEDs

Profit from its high luminous efficiency,small size,long life,energy saving and environmental protection,white light LED（WLED）has been widely used in the lighting industry.As an important part of WLED,phosphor properties will have an important impact on the luminous effect of WLED.Wide spectrum,simple production process and mature preparation technology are YAG:Ce³⁺phosphor advantages.Combining blue LED chips to realize WLED light source has become the main way to realize WLED light source.However,YAG:Ce³⁺phosphors have poor stability and easy to produce light decay applied to WLED lighting in actually,which reduces the luminescent properties of phosphors.Therefore,it is imperative to study ways to improve the luminous efficiency of YAG:Ce³⁺phosphors and improve the stability of powders.This paper aims to solve the above problems of YAG:Ce³⁺phosphors.Combined with different preparation methods of phosphors,surface modification and composite plasma effect materials etc,various characterization methods are used to study the luminous efficiency and thermal stability and moisture stability of YAG:Ce³⁺phosphors,in order to find ways to improve the luminous potential of phosphors.The specific research contents are as follows:1、The YAG:Ce³⁺phosphor was successfully prepared by high temperature solid phase method and sol-gel method.The YAG:Ce³⁺phosphor was prepared by two-step method based on(Y_1-xCe_x)₂O₃ precursor.The preparation method of the sample,the synthesis temperature,the phase structure of the rare earth ions,the micro structure,the morphology,the luminescence properties and the stability properties of the powder were investigated.The results show that the YAG:Ce³⁺phosphor’s best synthesis temperature is 1500℃by high temperature solid phase method,and the best doping of cesium ion is 1.33%.The YAG:Ce³⁺phosphor was prepared by two-step method based on(Y_1-xCe_x)₂O₃ precursor.The optimum doping concentration of cerium ions is 0.67%.The purity of the phosphor sample was higher than that of the traditional high-temperature solid phase method.The appearance is more uniform,the diameter of the particles is 2-5 um,and the particle size is nearly double that of the YAG:Ce³⁺phosphor sample prepared by the high temperature solid phase method.The luminescence centers of the YAG:Ce³⁺phosphor samples prepared by the two methods are all located at 535 nm.Compared with the powder prepared by the high temperature solid phase method,the luminescence intensity of the powder samples prepared based on the(Y_1-xCe_x)₂O₃ precursor is improved 14%.The powder samples prepared based on the(Y_1-xCe_x)₂O₃ precursor have better thermal stability and moisture resistance by comparison of high temperature and high humidity experiments.2、The SiO₂ nanospheres were successfully prepared by the Stober method,and the YAG:Ce³⁺@SiO₂ core-shell phosphor was further synthesized.The effect of the coating on the luminescence properties as well as the thermal and moisture resistance of the phosphor were investigated comprehensively.The results show that the YAG:Ce³⁺@SiO₂ core-shell phosphor with the uniform morphology can be obtained by improving the coating parameters.When the coating particle size is about 100nm,the surface defects of the powder is improved and the luminous intensity is increased by 34%compared with the behaviors of YAG:Ce³⁺phosphor.The high temperature and high moisture experiments were designed and realized successfully.Compared with YAG:Ce³⁺phosphor under the same experimental conditions,the luminous intensity attenuation value of YAG:Ce³⁺@SiO₂ phosphor at 180℃temperature and180℃corresponding humidity are decreased by 4%and 8%respectively.Surface modification technology can improve the thermal stability and moisture resistance of phosphors.3、The TiO₂ nanoparticles were successfully coated on the surface of YAG:Ce³⁺phosphor particles by a sol-gel method.TiO₂-coated YAG:Ce³⁺fluorescence was excited by an excitation source at 460 nm wavelength under optimized conditions of C₁₆H₃₆O₄Ti（TTBO）:H₂O=2:1（volume ratio）compared to uncoated YAG:Ce³⁺phosphor.The powder makes the luminescence intensity of the coated powder significantly improved by²1%,which is attributed to the localized surface plasmon resonance（LSPR）effect at the interface between the TiO₂ coating and the phosphor surface.When the preparation temperature of the TiO₂ coated phosphor is 600℃,the PL intensity of the phosphor can be improved due to the positive effect of the higher anatase content and the spherical particle shape of TiO₂ on the LSPR effect.Therefore,the technology of coating the phosphor with TiO₂ nanoparticles can be applied to the WLED without using the conventional metal plasma material and utilizing the LSPR effect of the semiconductor material.