Revealing Atomic‐Level Surface Passivation of PbI 2 ‐Reconditioned Red Perovskite Quantum Dots

CsPbI 3 perovskite quantum dots (QDs) are promising materials for high‐efficiency and low‐cost red fluorophores in advanced display and light‐sensing applications. However, structural and spectral stabilities of CsPbI 3 QDs by traditional preparation are seriously broken in water or light environment. Here, a compositional engineering strategy with an additional PbI 2 ‐recondition process to synthesize highly‐stable CsPbBr 1.2 I 1.8 @ SiO 2 QDs is demonstrated. Time‐ and temperature‐dependent photoluminescence and Raman measurements prove that spectral stability and exciton binding energy of QDs are greatly improved within this strategy. Notably, high‐resolution structure characterizations, point‐to‐point diffraction patterns and line‐scanning of element distributions provide strong and direct evidence at atomic‐level to reveal that PbI 2 ‐recondition can repair defects well, which helps to construct perfect lattices and homogeneous SiO 2 passivation layers to prevent the surface bonding of molecules. Moreover, our red perovskite QDs are further designed to prepare various anti‐counterfeiting labels as multi‐scale complex patterns to store and protect information. The proposed recondition strategy explores a new avenue to prepare stable and high‐quality red perovskite QDs for new‐generation lighting and light‐sensing devices.