Investigation on the effect of vacuum annealing time on structural and optical properties of YAG:Ce nanoparticles prepared by mixed-fuel microwave solution combustion synthesis

Abstract

Cerium doped yttrium aluminum garnet (YAG:Ce) nanoparticles were synthesized via mixed-fuel microwave solution combustion synthesis and further optimized by post annealing treatment. The effects of vacuum annealing time and ambient on the phosphor structural, morphological, compositional, and optical properties were investigated in detail. The structural study performed with X-ray diffraction analysis and Rietveld refinement revealed a direct crystallization from amorphous into single phase YAG:Ce was achieved at 1050 °C for 1 h. The increase in annealing time enhances the powder crystallinity and promotes crystal growth to form larger particles (50–85 nm). However, prolonged annealing would cause the partial oxidation of Ce3+ into optically inert Ce4+ ions, which was likely due to the increased Ce segregation. X-ray photoelectron spectroscopy evidenced that vacuum annealing has a higher tendency to suppress Ce3+ oxidation in comparison to air annealing, resulting in a significant enhancement of photoluminescence emission intensity by 20%. The optimum emission intensity was obtained for YAG:Ce nanoparticles after 5 h of vacuum annealing treatment with color coordinates of (0.391, 0.569). The white light emitting diode (WLED) fabricated with the optimized YAG:Ce nanoparticles showed a cool-white light with a maximum luminous efficacy of radiation of 285 lm/W and a corresponding color rendering index of 83.