Preparation And Luminescence Properties Investigation Of Ca₂MHf₂?AlO₄?₃:Ce³⁺?M=Y,Gd,La? Phosphors With Garnet Structure For W-LED Application

In recent years,white light-emitting diodes?W-LED?have been regarded as ideal lighting sources due to their high efficiency and environmental friendliness.Phosphor is an important part of W-LED,which greatly affects the performance of W-LED.Currently,the commercial green phosphors are?-Sialon:Eu²⁺,Lu₃Al₅O₁₂:Ce³⁺and Ca₃Sc₂Si₃O₁₂:Ce³⁺.Although they have been commercialized,they still suffer from lack of variety,complex manufacturing process,low color purity and poor thermal stability.Therefore,there is urgent need to develop a new green phosphor with high efficiency and excellent thermal stability.This paper focuses on solving the above problems via designing and synthesizing a new garnet structure green phosphor Ca₂MHf₂?AlO₄?₃:Ce³⁺?M=Y,Gd,La?for W-LED application for the first time,the luminescence performance and related mechanisms are systematically studied.The specific work is as follows:?1?The green phosphors of Ca₂Y_1-xHf₂?AlO₄?₃:xCe³⁺?0?x?0.06?were synthesized by high-temperature solid-phase method.The phase purity and structure information of the samples were determined by XRD spectrum and Rietveld refinement results.The morphology and microstructure of the sample were analyzed by using SEM,TEM and HRTEM.The luminescence performance and thermal stability are discussed in detail by the diffuse reflectance spectrum,excitation emission spectrum,quantum efficiency,fluorescence lifetime curve and thermal quenching spectrum.The results showed that the optimal excitation wavelength of the prepared sample was at 410 nm,which was consistent with the results of the diffuse reflection spectrum,and the emission spectrum exhibited an asymmetric broad band centered at 490 nm with a full wave at half maximum about 90 nm.The optimal doping concentration point of Ce³⁺in Ca₂YHf₂?AlO₄?₃ was x=0.03,and the quantum efficiency is confirmed to be 73.8%.The thermal quenching test results showed that when the temperature was 120?,the emission intensity of Ca₂YHf₂?AlO₄?₃:0.03Ce³⁺still reached about 70%of the initial intensity.Finally,Ca₂YHf₂?AlO₄?₃:0.03Ce³⁺was nitrided to further improve thermal stability.?2?Ca₂Gd_1-xHf₂?AlO₄?₃:x Ce³⁺?0?x?0.06?series green phosphors were synthesized for the first time based on the above work.The phase purity,elemental composition,luminescence performance and thermal stability were discussed in detail.The results showed that the prepared samples were single-phase,and the optimal excitation wavelength was at 412 nm,the emission spectrum showed an asymmetric broad band centered at 495 nm with a full wave at half maximum about 100 nm.The optimal doping concentration point of Ce³⁺was x=0.03 with quantum efficiency of 60.2%.The emission intensity Ca₂GdHf₂?AlO₄?₃:0.03Ce³⁺could still reach 54%of the initial intensity when the temperature rose to 120?.?3?The Ca₂La_1-xHf₂?AlO₄?₃:xCe³⁺?0?x?0.05?series green phosphors were synthesized for the first time.The phase purity and elemental composition of the samples were determined by XRD and EDS spectrum,the luminescence properties and thermal stability of Ca₂LaHf₂?AlO₄?₃:Ce³⁺sample were discussed in detail.The test results showed that the optimal excitation wavelength of the prepared phosphor was about 425 nm,and the emission spectrum illustrated an asymmetric broad band centered at 512 nm with a full wave at half maximum about 110 nm.The optimal doping concentration point of Ce³⁺was x=0.03 with quantum efficiency of 18.7%.The thermal quenching test results showed that the Ca₂LaHf₂?AlO₄?₃:0.03Ce³⁺sample can still maintain 51%of its initial intensity when the temperature reached 120?.Finally,by analyzing the CIE color coordinate diagram of the samples,it can be seen that the color coordinates of the Ca₂La_1-xHf₂?AlO₄?₃:xCe³⁺?0?x?0.05?series of phosphors were located in the standard green zone.