Bright Self‐Trapped Exciton Emission of CsPbBr ₃ @CsPb ₂ Br ₅ Nanostructures Created by Dissolution and Recrystallization of Hydrophilic Cu:CsPbBr ₃

Nanoarchitectonics provide significant opportunities to endow materials with special photoluminescence (PL) properties. In this paper, novel self‐trapped exciton (STE) orange‐red emission is observed by creating CsPbBr 3 @CsPb 2 Br 5 nanostructures through controlling the dissolution and recrystallization of Cu:CsPbBr 3 . Due to the dissolution and phase transfer of CsPbBr 3 , CsPbBr 3 @CsPb 2 Br 5 nanostructures are formed. Cu + instead of Pb 2+ induced significant lattice distortion and formed a multi‐core@shell configuration, promoting STE emission center establishment and enabling the broad orange‐red PL peak (620 nm) of CsPbBr 3 components with a PL quantum yield (PLQY) of 45.6%. The CsPb 2 Br 5 shell effectively isolated the nanostructure from moisture and oxygen, resulting in extraordinary stability under ambient, ultraviolet light irradiation, and aqueous solutions. Cu + component is a key for the STE emission because Na:CsPbBr 3 @CsPb 2 Br 5 sample prepared using the same procedure revealed a narrow green PL peak (516 nm) even though the PLQY increased to 82.8% from 55.4%. Na:CsPbBr 3 @CsPb 2 Br 5 sample exhibited a single‐core@shell structure, in which Na + tends to occupy interstitial sites, effectively passivating deep‐level defects. Because of high stability, an light emitting diode was fabricated using Cu:CsPbBr 3 @CsPb 2 Br 5 to show stable warm‐orange emission with a correlated color temperature of 1430 K, and a color rendering index of 62, suggesting potential solid‐state lighting applications.