Highly Efficient Broadband Near-Infrared Emission from Sn2+ Alloyed Lead-Free Cesium Zinc Halides

Abstract

Luminescent metal halides have attracted increasing attention because of their tunable emission and superior photoelectric properties. However, it is still challenging to achieve near-infrared (NIR) emission from metal halides, which is important in applications such as food quality analysis and night vision. In this work, the broadband NIR emission is achieved by alloying Sn2+ into zero-dimensional (0D) Cs2ZnBr4. The incorporating of Sn2+ cations enables the originally weakly luminescent Cs2ZnBr4 to exhibit an efficient broadband NIR emission. Upon photoexication, the optimized Sn2+ alloyed Cs2ZnBr4 (Cs2Zn0.875Sn0.125Br4) exhibits a highly efficient broadband NIR emission peaked around 700 nm, with a large Stokes shift of 323 nm, a full width at maximum of 177 nm, and a high quantum efficiency of around 41%. Spectroscopic and theoretical calculations unveil that the efficient NIR emission originates from the self-trapping emission introduced by the Sn alloying. In addition to the high efficient broadband emission, the Sn2+ alloyed Cs2ZnBr4 also exhibits high thermal stability, retaining 78% of its initial intensity at 150 °C. The night vision application is demonstrated by using a light source fabricated by combining Sn2+ alloyed Cs2ZnBr4 phosphor with a 365 nm LED chip in the dark.