Interfacial B-Site Ion Diffusion in All-Inorganic Core/Shell Perovskite Nanocrystals.

All-inorganic metal halide perovskites (ABX, X = Cl, Br, or I) show great potential for the fabrication of optoelectronic devices, but the toxicity and instability of lead-based perovskites limit their applications. Shell passivation with a more stable lead-free perovskite is a promising strategy to isolate unstable components from the environment as well as a feasible way to tune the optical properties. However, it is challenging to grow core/shell perovskite nanocrystals (NCs) due to the soft ionic nature of the perovskite lattice. In this work, we developed a facile method to grow a lead-free CsMnCl shell on the surface of CsPbCl NCs to form CsPbCl/CsMnCl core/shell NCs with enhanced environmental stability and improved photoluminescence (PL) quantum yields (QYs). More importantly, the resulting core/shell perovskite NCs have color-tunable PL due to B-site ion diffusion at the interface of the core/shell NCs. Specifically, B-site Mn diffusion from the CsMnCl shell to the CsPbCl core leads to a Mn-doped CsPbCl core (i.e., Mn:CsPbCl), which can turn on the Mn PL at around 600 nm. The ratio of Mn PL and host CsPbCl PL is highly tunable as a function of the thermal annealing time of the CsPbCl/CsMnCl core/shell NCs. While the halide anion exchange for all-inorganic metal halide perovskites has been well-developed for band-gap-engineered materials, interfacial B-site diffusion in core/shell perovskite NCs is a promising approach for both tunable optical properties and enhanced environmental stability.