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.