Realizing Color‐Tunable and Time‐Dependent Ultralong Afterglow Emission in Antimony‐Doped CsCdCl3 Metal Halide for Advanced Anti‐Counterfeiting and Information Encryption

Abstract Long afterglow luminescent materials have captured intense attention for their unique applications in biological imaging, photodynamic therapy, and optical anti‐counterfeiting. However, achieving highly efficient and tunable ultralong afterglow emission in all‐inorganic metal halides is an open challenge. Herein, Sb 3+ ‐doped hexagonal CsCdCl 3 metal halide is reported via hydrothermal reaction. Upon photoabsorption, the as‐synthesized compounds exhibit dual‐emission bands with a photoluminescence quantum yield (PLQY) of 59.6%, which can be attributed to the self‐trapped exciton emission out of the strong electron‐phonon coupling. After ceasing excitation of 365 nm, bright afterglow emission with the longest duration lasting up to 5000 s is witnessed in Sb 3+ ‐doped CsCdCl 3 . More importantly, the color‐tunable and time‐dependent ultralong afterglow emission is realized via regulating the doping concentration of Sb 3+ , which should be due to the trap electrons increase gradually under high doping concentration. Given this unusual afterglow emission characteristics, the optical anti‐counterfeiting and information encryption are constructed based on as‐synthesized compounds. These findings not only help further understand the tunable afterglow emission mechanism in all‐inorganic metal halides, but also provide a new strategy for designing novel ultralong afterglow luminescent materials.