Heterovalent Doping Enabled Efficient and Stable Extrinsic Self‐Trapped Exciton Emission in Zero‐Dimensional Cesium Zinc Halides

Abstract Lead‐free metal halides with 0D crystal structures have stimulated the interest of researchers due to their remarkable photoelectric capabilities, long‐term stability, and environmentally friendly nature. Here, an efficient cyan‐emitting copper(I)‐doped 0D cesium zinc halide is developed via a simple solution synthesis approach and valence stabilization strategy. The broad emission band, substantial Stokes shift, and relatively long decay time all point to extrinsic self‐trapped excitons as the source of the emission. The photoluminescence quantum yield increases from 85.3% to 93.6% after codoping with Al 3+ at Zn sites, which can be attributed to an increase in distortion of [CuCl 4 ] 3‐ polyhedrons caused by a decrease in local structure symmetry. Meanwhile, the environmental stability of Cu + ‐Al 3+ codoped samples is also boosted significantly by the distortion‐assisted charge compensation effect. Density functional theory calculations and investigations of temperature‐dependent photoluminescence behaviors back up the luminescence mechanism proposed above. The current study provides new possibilities for developing copper(I)‐relevant metal halides with high luminescence efficiency and excellent environmental stability.