Rare-Earth Substitution of La<sub>3</sub>Si<sub>2</sub>S<sub>8</sub>I for Efficient and Color-Tunable Phosphor Converted White Light Emitting Diodes
Trinanjan Dey, Dundappa Mumbaraddi, Razieh Firouzi-Haji, Dmitry Vrublevskiy, Z. Lin, A. Meldrum, Arthur Mar
Abstract
Mixed-anion compounds enable properties to be controlled to a greater degree by chemical substitution than single-anion compounds. La 3 Si 2 S 8 I was investigated as a host to develop phosphors based on solid solutions (La 1– x RE x ) 3 Si 2 S 8 I ( RE = Ce, Pr, Tb, Dy, Ho; x = 0–0.33) and (La 1– x – y Ce x RE y ) 3 Si 2 S 8 I ( 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 RE 3+ concentration, the spectra featured broad emission (cyan for Ce 3+ ) or sharp 4f–4f emission peaks (red for Ho 3+; green for Tb 3+; cyan-green and red for Pr 3+; yellow and cyan for Dy 3+ ) which can be fine-tuned to a wider gamut. The cosubstituted (La 1– x – y Ce x RE y ) 3 Si 2 S 8 I phosphors showed even more intense photoluminescence and wider color palettes within the cyan to green regions (Ce 3+ –Tb 3+ ) and cool to warm white (Ce 3+ –Dy 3+ ). 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 Ce 3+ ) to 3–450 μs (for other RE 3+ ). 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.