LuGdAG:Ce ceramic compositions as promising candidates for high CRI white light emitting diodes

Abstract

In this study, powders of LuGdAG:Ce oxide compositions with gadolinium content ranging from 0 to 100 at.% were synthesized using the chemical precipitation method. The influence of the nominal composition on the kinetics of phase transformations, as well as the particle size distribution and morphology of the powders, was investigated. Ceramic samples of LuGdAG:Ce were produced from these ceramic powders. A comparison with reference materials revealed differences in the properties of LuGdAG:Ce ceramics obtained from chemically precipitated powders versus those synthesized through solid-phase reactive sintering. The examination of the optical and luminescent properties of the ceramic samples indicated that as the proportion of gadolinium increases, the light transmittance of the ceramics also increases at a vacuum sintering temperature of 1740°C. In addition, as the gadolinium content increased, there was a shift in the luminescence spectrum toward the red region, a decrease in correlated color temperature, a reduction in luminescence efficiency, and an increase in the color rendering index. When comparing the luminescent characteristics of LuGdAG:Ce and YAG:Ce ceramics with the same cerium content, it was found that YAG:Ce exhibits higher efficiency and brightness but a lower color rendering index. The highest color rendering index (Ra ≈ 77) was recorded for Ce0.01Lu1.19Gd1.8Al5O12 ceramics, which is a notable achievement for single-phase ceramics with a garnet structure. These results confirm that LuGdAG:Ce ceramics hold promise for use in warm white light sources with a high color rendering index, including high-power laser-excited sources.