Kinetically Trapped High‐Density Interstitial Mn 2+ Enables Concentration‐Quenching‐Free Persistent Luminescence in CsCdCl 3 Perovskites

Long‐persistent luminescence materials commonly suffer from concentration quenching at high dopant levels, limiting simultaneous optimization of luminescent centers and trap states. Herein, we report a kinetically controlled room‐temperature strategy for high‐density interstitial Mn 2+ doping in CsCdCl 3 perovskites. Using cetyltrimethylammonium bromide as both bromine source and crystallization modulator, rapid nucleation kinetically traps Mn 2+ ions at interstitial sites within a Br–expanded lattice, bypassing thermodynamically favored substitutional incorporation. This nonequilibrium doping configuration effectively suppresses Mn 2+ aggregation and breaks the concentration‐quenching limit of conventional substitutional doping, enabling efficient emission even at 20% Mn 2+ loading. The cooperative halide–interstitial doping further establishes a hierarchical trap landscape with optimized carrier trapping and release behavior. Consequently, the material exhibits a near‐unity photoluminescence quantum yield of 94.2%, ultralong persistent luminescence exceeding 4000 s, continuously tunable afterglow emission, and anomalous thermally enhanced luminescence over 77–407 K. The synthesis is completed within 20 s at room temperature and is readily scalable to gram‐level production. Multifunctional applications including optical thermometry, rewritable information storage, and dynamic anti‐counterfeiting are further demonstrated.