Improved Energy Transfer in Mn-Doped Cs 3 Cu 2 I 5 Microcrystals Induced by Localized Lattice Distortion.

With nontoxicity and high emission efficiency, luminescent copper(I)-based halides have attracted much attention as alternatives for lead-based perovskites in photoelectric domains. However, extending the emission wavelength by doping with Mn in a facile way is still a challenge. In this work, Mn-doped CsCuI microcrystals were synthesized by a mild solution method, and double emission bands from self-trapped excitons (STEs) and Mn peaking at 445 and 560 nm, respectively, were observed. More importantly, further introduction of alkali metal ions (Rb, K, Na) considerably promoted the luminescence performance of the CsCuI-Mn microcrystals. The STE → Mn energy transfer efficiency of the typical sample doped with Na increased from ∼0 to 21.30%, and the photoluminescence quantum yield (PLQY) increased from 47.32% to 62.06%. The detailed structural and optical characterizations combined with DFT calculations proved that the doping with alkali metal ions causes lattice distortion and enhances the coupling between [MnI] and [CuI] tetrahedra, thus promoting the energy transfer efficiency and the PLQY.