Tunable Single-Phase White-Light Emission in Double Perovskite Cs 2 NaGdCl 6 : Sb 3+ /Tb 3+ /Sm 3+ for Plant Growth Lighting and Advanced Optical Information Encryption

Lead-free double perovskites are ideal candidates for phosphors in white-light-emitting diodes (WLEDs), yet achieving efficient, tunable single-phase white-light emission remains challenging. Herein, single-phase white-emitting phosphors are synthesized via the synergistic Sb3+/Tb3+/Sm3+ codoping into Cs2NaGdCl6. Steady-state and transient spectra reveal three energy transfer channels: Sb3+ → Tb3+, Sb3+ → Sm3+, and Tb3+→Sm3+. Furthermore, a cascade Sb3+ → Tb3+ → Sm3+ energy transfer pathway is constructed to interlock emission intensities, enabling continuous cool-to-warm white light tuning via Tb3+ concentration adjustment. The optimized sample exhibits a quantum yield of 53.75%; notably, it maintains 84.03% of its emission intensity at 423 K. The fabricated WLED device displays near-standard white coordinates (0.3304, 0.3676), a color rendering index of 88.2, and a 91.12% spectral match with chlorophyll b absorption. Additionally, multichannel luminescence enables pixelated arrays and encrypted quick response codes, decodable only under UV excitation with a specific narrow-band filter key. This work proposes a strategy for optimizing single-phase white light and expands lead-free perovskite applications in information security and plant lighting.