From Nonluminescent CsPbX (X = Cl, Br, I) Nanocrystals to Highly Luminescent CsPbX Nanocrystals: Water-Triggered Transformation through a CsX-Stripping Mechanism.

We report a novel CsX-stripping mechanism that enables the efficient chemical transformation of nonluminescent CsPbX (X = Cl, Br, I) nanocrystals (NCs) to highly luminescent CsPbX NCs. During the transformation, CsPbX NCs dispersed in a nonpolar solvent are converted into CsPbX NCs by stripping CsX through an interfacial reaction with water in a different phase. This process takes advantage of the high solubility of CsX in water as well as the ionic nature and high ion diffusion property of CsPbX NCs, and produces monodisperse and air-stable CsPbX NCs with controllable halide composition, tunable emission wavelength covering the full visible range, narrow emission width, and high photoluminescent quantum yield (up to 75%). An additional advantage is that this is a clean synthesis as CsPbX NCs are converted into CsPbX NCs in the nonpolar phase while the byproduct of CsX is formed in water that could be easily separated from the organic phase. The as-prepared CsPbX NCs show enhanced stability against moisture because of the passivated surface. Our finding not only provides a new pathway for the preparation of highly luminescent CsPbX NCs but also adds insights into the chemical transformation behavior and stabilization mechanism of these emerging perovskite nanocrystals.