Photoluminescence properties of YAG:Ce, RE phosphors prepared by citric acid gel combustion method

(Y_0.99-xRE_x)₃ Al₅O₁₂:Ce_0.03 (RE=Lu, Gd, La) phosphors were successfully synthesized by sol-gel combustion method using citric acid as chelating agent and fuel.Through the analysis of XRD, FTIR, SEM, and photoluminescence spectrum (PL), the crystal structure, particle morphology and luminescent properties of YAG:Ce under different calcination temperatures and RE co-doped concentrations were investigated.The powders with nanocrystalline size were obtained only at 900°C.As the calcination temperatures increasing , the average particle size was from 50 nm to 200 nm. With decreasing ionic radius from La³⁺, Gd³⁺, to Lu³⁺, the ceiling concentration leading to phase transformation was gradually increasing. Doped with only 50 mol% of La³⁺, to replace Y³⁺sites, the main phase of sample had transformed into LaAlO₃. While the concentration of Gd³⁺, reached 90 mol%-99 mol%, the main phase of sample remained cubic YAG. Furthermore, Y³⁺ were completely replaced by Lu³⁺, with a cubic YAG. The location of the emission peak of Gd-codoped YAG:Ce³⁺system shifted to the red region, and it had a red shift of 21 nm corresponding to the maximum emission intensity before the appearance of GdAlO₃. It reached 33 nm when Y³⁺ sites were completely replaced by Gd³⁺. Additionally, it had a blue shift of 24 nm when Y³⁺ completely replaced by Lu³⁺. The model of configuration coordinate and the crystal field theory gave this phenomenon a reasonable explanation.