Rare-Earth Substitution of La

Mixed-anion compounds enable properties to be controlled to a greater degree by chemical substitution than single-anion compounds. La3Si2S8I was investigated as a host to develop phosphors based on solid solutions (La1-xREx)3Si2S8I (RE = Ce, Pr, Tb, Dy, Ho; x = 0-0.33) and (La1-x-yCexREy)3Si2S8I (RE = Tb, Dy; x, y = 0-0.33) that exhibit wide color tunability and white emission. Upon excitation with a 364 nm UV laser source, the phosphors emit through a down-conversion process over a wide visible color gamut. Depending on the RE3+ concentration, the spectra featured broad emission (cyan for Ce3+) or sharp 4f-4f emission peaks (red for Ho3+; green for Tb3+; cyan-green and red for Pr3+; yellow and cyan for Dy3+) which can be fine-tuned to a wider gamut. The cosubstituted (La1-x-yCexREy)3Si2S8I phosphors showed even more intense photoluminescence and wider color palettes within the cyan to green regions (Ce3+-Tb3+) and cool to warm white (Ce3+-Dy3+). The photometric parameters were appropriate for backlighting display and near UV-pumped phosphor-converted white light-emitting diodes (pc-wLEDs). Photoluminescence decay profiles follow biexponential behavior with lifetimes ranging from a few ns (for Ce3+) to 3-450 μs (for other RE3+). Most of the optimized phosphors were moderately stable at 80-100 °C before the onset of thermal quenching effects. They gave absolute quantum yields up to 50%, which are favorable for efficient energy conversion. Prototype pc-wLEDs fabricated from a blend of three phosphors or from single-phase phosphors showed promising performance.