Cation-Size Mismatch as a Design Principle for Enhancing the Efficiency of Garnet Phosphors

In this study, we report on the development of a new garnet phosphor with enhanced optical properties and cost reduction. Samples were prepared using the solid-solution method, in which the chemical unit and substitutions with cation-size mismatch were combined. Solid solutions between two garnet structure compounds, green phosphor Lu3Al5O12:Ce3+ (LuAG:Ce3+) and orange phosphor Lu2CaMg2Si3O12:Ce3+ (Lu3-x CaxAl2-2xMg2xAl3-3xSi3xO12:Ce3+), constituted the complete solid-solution range x (x = 0-1). The crystal structures of all the compounds were discerned through Rietveld refinement based on the X-ray diffraction patterns. The unique occupancy of {Lu/Ca}, [Al/Mg], (Al/Si), and O atoms in the solid-solution samples was identified. Optical properties were classified in terms of the excitation and emission spectra, quantum yield, and temperature-dependent photoluminescence intensity. To investigate the relationship between the structural and optical changes, Ba2+ ions (employed for cation-size mismatch) were substituted into dodecahedral and octahedral sites at various concentrations. Finally, we report the development of a new green garnet phosphor via the use of a solid-solution design and cation-size mismatch, the emission intensity of which was measured 116% higher than that of commercial LuAG:Ce3+.