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CsPbBr3 nanoplates (NPs) have shown great potential in diverse optoelectronic applications. Despite the wonderful luminescence properties, the inherent instability of these NPs hinders their use in practical situations. Herein, a facile water‐assisted strategy is reported to synthesize highly stable blue emission CsPbBr3 NPs encapsulated in PbBr(OH). The introduction of water directly into the reaction mixture is pivotal, as it triggers the transformation of bulk CsPbBr3 nanocubes into 2‐D CsPbBr3 NPs within the PbBr(OH) matrix, resulting in the formation of CsPbBr3@PbBr(OH) microbricks. Remarkably, the water content in the reaction mixture allows the control of the number of perovskite layers in the NPs, thus enabling the emission color to be tuned from deep blue to green. The unconventional approach presented herein not only offers a cost‐effective pathway to synthesize blue‐emitting perovskites which are highly stable in a wide variety of polar and non‐polar solvents, but also holds immense potential for propelling the advancement of high‐performance LEDs and other optoelectronic devices. The findings underscore the significance of water in dictating the growth dynamics and emission characteristics of perovskite NPs, paving the way for their practical application. [ABSTRACT FROM AUTHOR]

Quantum‐confined perovskite CsPbBr3 Nanoplatelets (NPLs) have recently emerged as promising blue‐emitting materials for perovskite light‐emitting diodes (PeLEDs). Yet, their susceptibility to optical instability in solid films under ambient conditions poses a significant hindrance. This study introduces a novel chelating strategy that utilizes metal manganese ions and multidentate ligands, markedly improving the structural stability, and emission efficiency of NPLs. The approach involves adding Diethylenetriaminepentaacetic acid (DTPA) to the perovskite precursor solution, which allows for strong coordination to surface [PbBr6]4− octahedrons via its multiple chelation sites. Ensuing metal manganese ion integration during the purification phase addresses Pb2+ and Br− site vacancies, culminating in near‐perfect octahedral structures with significantly fewer vacancies. These metal manganese ions are then further immobilized on the NPLs surface by the chelating effect of unbound DTPA functional groups. The resultant CsPbBr3 NPLs films demonstrate an impressive PLQY of 66%, showcasing remarkable air stability with consistent blue emission for up to 5 days. The CsPbBr3 NPLs‐based PeLEDs show electroluminescence at 460 nm with a current efficiency of 1.07 cd A−1 and a maximum luminance of 220 cd m−2. The proposed chelating strategy positions perovskite NPLs as an extremely promising prospect in future applications of high‐definition displays and high‐quality lighting. [ABSTRACT FROM AUTHOR]