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 Lu 3 Al 5 O 12:Ce 3+ (LuAG:Ce 3+ ) and orange phosphor Lu 2 CaMg 2 Si 3 O 12:Ce 3+ (Lu 3– x Ca x Al 2–2 x Mg 2 x Al 3–3 x Si 3 x O 12:Ce 3+ ), 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, Ba 2+ 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:Ce 3+ .