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⁺ (Lu_3-xCaxAl_2-2xMg_2xAl_3-3xSi_3xO₁₂: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⁺. © 2020 American Chemical Society.