A Multifunctional Fe ³⁺ ‐Activated Garnet Phosphor Enabling Near‐Infrared Imaging and Photochromic Information Encryption

Near‐infrared phosphor‐converted light‐emitting diodes (NIR pc‐LEDs) are emerging as compact and energy‐efficient light sources for next‐generation optical technologies. Nevertheless, the development of Cr 3+ ‐free NIR phosphors that simultaneously deliver wideband luminescence, superior biocompatibility, and tunable photo‐physical properties remains a formidable challenge. Here, we propose novel La 3 Sc 2 Ga 3 O 12 :Fe 3+ phosphors featuring broadband NIR emission enabled by crystal‐field engineering. Precise regulation of Fe 3+ concentration markedly reinforces the excitation band centered at 417 nm, ensuring high compatibility with commercial LED chips. Furthermore, Li + incorporation heals the lattice environment and suppresses non‐radiative relaxation, substantially amplifying NIR emission. The optimized composition exhibits robust thermal stability, retaining 57.45% of its emission intensity at 423 K, together with pronounced and reversible photochromic behavior. Integrating it with a 420 nm chip yields a high‐power NIR pc‐LED prototype. The material demonstrates multifunctional optical responsiveness suitable for secure photonic encoding and intelligent sensing platforms. These findings establish valuable insights for design of new NIR materials and the development of advanced intelligent devices.