Cationic Substitution-Enabled Green-Emitting Gd2–yYyLuAl4GaO12: Ce3+ Garnet Phosphors with High Quantum Efficiency and Superior Thermal Stability for Advanced WLEDs

A novel garnet-type phosphor, Gd2–yYyLuAl4GaO12: Ce3+, was synthesized via a high-temperature solid-state reaction to address the demand for efficient green-emitting materials in solid-state lighting. By employing a cation substitution strategy (Y3+/Gd3+ codoping), the photoluminescence performance was significantly enhanced: the quantum efficiency increased from 86.79 to 96.86%, accompanied by a tunable emission shift from yellow to green (560–520 nm). Moreover, the thermal stability at 423 K improved dramatically from 40.79 to 92.98%, surpassing those of commercial green phosphors. Structural and spectral analyses revealed that the optimized crystal field splitting and enhanced lattice rigidity, induced by cation substitution, effectively suppressed nonradiative transitions, thereby boosting both quantum efficiency and thermal stability. A prototype white light-emitting diode (WLED) fabricated with Y2LuAl4GaO12: Ce3+ phosphor exhibited excellent performance, including a high color rendering index (Ra = 91), low correlated color temperature (CCT = 3043 K), and good color stability under varying driving currents. These findings highlight the significant promise of Gd2–yYyLuAl4GaO12: Ce3+ as a superior green-emitting phosphor for advanced WLED systems, providing a feasible pathway for designing outstanding thermal stability and color-tunable luminescent materials via cationic engineering.