Efficient Double Perovskite Cs ₂ NaGdCl ₆ : Sb ³⁺ /Pr ³⁺ for Plant‐Cultivation Lighting, Advanced Optical Anti‐Counterfeiting, and WLED Applications

Developing multifunctional luminescent materials with tunable spectra is crucial for plant lighting and information–security applications. To address the critical requirement of plant photosynthesis for blue and red spectral components, a novel lead‐free double perovskite Cs 2 NaGdCl 6 : Sb 3+ , Pr 3+ phosphor was designed and synthesized via a hydrothermal method. By incorporating Sb 3+ ions with an ns 2 electronic configuration, broadband blue emission originating from self‐trapped excitons (STEs) was induced within the host lattice. Concurrently, the stability and electron–phonon coupling strength of this STE emission were systematically investigated. Furthermore, the introduction of Pr 3+ established an efficient energy transfer channel (Sb 3+ → Pr 3+ ), activating red emission at 652 nm derived from the 3 P 0 → 3 F 2 transition, enabling efficient dual‐band blue–red luminescence. The fabricated single‐phase light‐emitting diode (LED) achieved a 90.28% spectral match with chlorophyll b absorption, along with an internal quantum efficiency of 49.81% and an external quantum efficiency of 29.41%. Leveraging the distinct excitation responses and spectral tunability across the series of materials, a multilevel dynamic anti‐counterfeiting system integrating excitation selectivity and narrow‐band gating was constructed. Additionally, a high‐performance white LED device was realized based on Cs 2 NaGdCl 6 : 0.01Sb 3+ , 0.15Pr 3+ , yielding a high color rendering index of 93.1, a correlated color temperature of 4790 K, and chromaticity coordinates of (0.35, 0.37). This work not only presents a high‐performance material for plant lighting and display applications but also provides new insights into the functional design of lead‐free double perovskite phosphors.