Achieving Ultralong Red Afterglow Emission in Mn ²⁺ ‐Doped NH ₄ CdCl ₃ Hybrid Perovskite Through Trap State Modulation

Abstract Organic–inorganic hybrid perovskites (OIHPs) show great potential for long afterglow luminescence owing to their adjustable structures and exceptional optoelectronic properties. However, achieving stable, ultra‐long afterglow emission remains a challenge, primarily because of the limitations of triplet exciton phosphorescence. This paper presents a novel Mn ²⁺ ‐doped NH ₄ CdCl ₃ perovskite single crystal with ultra‐long red afterglow emission. By introducing defect states through doping, afterglow emission is realized independently of triplet exciton phosphorescence. Under 254 nm excitation, the crystal exhibits a red afterglow lasting up to 2400 s, with controllable trap depth and concentration by adjusting the Mn ²⁺ doping levels, thus tuning the afterglow duration. Additionally, the crystals demonstrate excellent photoluminescence (PL) under high‐temperature and humid conditions. Information encryption patterns are also developed based on materials with varying doping concentrations, demonstrating their potential for anti‐counterfeiting and encryption applications. This study provides a new strategy for achieving ultra‐long afterglow in organic–inorganic hybrid perovskites.