Preparation And Optical Properties Of Ce:YAG Fluorescent Ceramics

LED solid-state lighting has a very broad application prospect and huge market value due to the advantages of energy saving and environmental protection,long service life,fast response time and small size of components.Luminescence efficiency is an important optical parameter of LED,the current mainstream way to realize white light LED is through the combination of Ce:YAG yellow phosphor and blue chip,using organic resin with low thermal conductivity packaging,the phosphor efficiency is unstable and is prone to thermal quenching.In order to improve the LED luminescence efficiency,Ce:YAG fluorescent ceramics with high thermal stability and excellent mechanical properties can be used as fluorescence conversion material.At present,for the relationship between fluorescent ceramic luminescence efficiency and annealing process,especially Ce with high cerium ion concentration:YAG ceramic packaging high brightness yellow LED light source（565-590 nm）is still low.This paper explores the quantum efficiency of fluorescent ceramics and by introducing high thermal conductivity of Al₂O₃.The specific research contents of the paper are as follows:（1）The effect of annealing process on the optical properties of high cerium ion concentration of 1.0 at%Ce:YAG ceramics was studied.It is found that the annealing process can not only eliminate the oxygen vacancy defects inside the ceramic and improve the quantum efficiency,but also oxidize Ce³⁺to Ce⁴⁺with smaller ion radius,reduce the concentration of luminescent ions and form pores.When the annealing temperature was increased from 900 ^oC to 1400 ^oC,the more obvious the Ce³⁺oxidation degree was,and the linear transmittance of the ceramic at 550 nm was also decreased from 81.45%to 46.19%.In addition,the formed pore can act as an additional scattering center to change the light propagation path and improve the conversion efficiency of the excitation light.（2）Explore the relationship between cerium ion concentration,annealing temperature and luminescence efficiency in Ce:YAG-based CB-LEDs.The results show that controlling the annealing temperature can achieve the"balance"between the number of internal defects and the luminous ion concentration.As the cerium ion concentration increased from 0.2 at%to 1.0 at%,the optimal annealing temperature of Ce:YAG ceramics gradually decreased from 1200 ^oC to 900 ^oC,and the optical flux of the corresponding CB-LEDs increased by 8.98%（1200 ^oC）,8.56%（1100 ^oC）,9.65%（1000 ^oC）,6.99%（900 ^oC）and 8.23%（900 ^oC）.（3）High-brightness yellow light（565-590 nm）is achieved by adjusting the concentration of Gd³⁺and Ce³⁺in（Ce,Gd）:YAG ceramics.Since LED packaging structure usually requires ceramic thickness less than 200μm and Gd³⁺to reduce the material quenching temperature,select(Ce_0.6%Y_69.4%Gd_30%)₃Al₅O₁₂ceramics as composite ceramic matrix material with emission spectrum peak of 568 nm,CCT3107 K,CRI 55.5 and color coordinates（0.4708,0.4899）.（4）In order to improve the luminescence efficiency of(Ce_0.6%Y_69.4%Gd_30%)₃Al₅O₁₂ceramics,Al₂O₃second phase preparation of composite ceramics was introduced to study the relationship between Al₂O₃composite ratio,working temperature and luminescent efficiency of CB-y LEDs excited at 450 nm.The results show that the Al₂O₃content increased from 0 wt%to 40 wt%,the thermal conductivity of composite ceramic increased from 7.244 W/（m·K）to 13.944 W/（m·K）.The temperature difference between ceramic（T_c）and matrix（T_s）of working CB-LEDs gradually decreased from 17.3 ^oC to 10.9 ^oC,and the steady state temperature of ceramic gradually decreased from 141.1 ^oC to 132.2 ^oC.Among them,(Ce_0.6%Y_69.4%Gd_30%)₃Al₅O₁₂-40wt%Al₂O₃ceramics is up to 109.49 lm/W,8.54%higher compared to(Ce_0.6%Y_69.4%Gd_30%)₃Al₅O₁₂ceramics.