Glycothermally synthesized YAG:Ce³⁺ nanophosphors for blue LEDs

Ce³⁺-doped yttrium aluminum garnet nanoparticles are prepared from yttrium acetate tetrahydrate, cerium acetate monohydrate, and aluminum isopropoxide by autoclave treatment in 1,4-butanediol at 300°C for 2 h. Optical and structural properties of nanoparticles are characterized as compared to micrometer-sized particles. A transparent film can be produced from the paste of nanoparticles. The back side of the film is excited by blue light and the photoluminescence intensity due to the 5d → 4f transition of Ce ³⁺ is measured in the front side of the film. The photoluminescence intensity of the film containing nanoparticles is proportional to the film thickness, while that of the film containing micrometer-sized particles reaches a saturated value. This result shows that the transparent film of nanoparticles has markedly low light scattering loss. The gradual decrease in the photoluminescence intensity for nanoparticles is observed under the continuous excitation of blue light. This photobleaching behavior is not observed for micrometer-sized particles. The photobleach is attributed to the photooxidation of Ce³⁺ to Ce⁴⁺ near surface of nanoparticles and can be suppressed for the sealed transparent film containing nanoparticles.