Ce3+ and Eu3+ emissions in YAG via a core-shell strategy for warm white LED lighting

YAG:Ce and YAG:Eu sols were synthesized by a polymeric sol-gel route. The crystallization temperature of YAG was determined by X-ray diffraction as a function of the calcination temperature, revealing that YAG starts to crystallize directly from the amorphous phase at 800 A degrees C. The effects of the thermal treatment and the dopant amount on the photoluminescent properties were studied, observing the highest emission after calcination at 1000 A degrees C for 1 h in both cases and with a concentration of 1 and 3 mol% of Ce and Eu, respectively. Core-shell materials were prepared by dipping YAG:Ce or YAG:Eu sintered pellets into the synthesized sols and then, these materials were calcined at 1000 A degrees C for 1 h. An effective energy transfer from Ce to Eu was observed in the sample YAG:Eu (core)-YAG:Ce (shell) when blue light (lambda = 465 nm) is used as excitation source. This wavelength excites the Ce but not the Eu; however, in the photoluminescence emission spectrum, the bands associated to both ions can be clearly detected, confirming that the core-shell strategy is a good method for the preparation of warmer white LEDs. [GRAPHICS] .