Broadband NIR-II Emission with Wide Excitation Range in Cs₂WCl₆ Double Perovskites Utilizing Re⁴⁺ Doping

Halide double perovskites with near-infrared (NIR) emission are promising for optoelectronic applications. NIR-II (1000-1700 nm) emission, in particular, is attractive due to its strong tissue penetration, high spatial resolution, and low biological light damage risk. However, materials capable of NIR-II emission often require additional sensitizers and suffer from issues such as narrow emission bandwidth and low photoluminescence efficiency. In this work, we report a Re⁴⁺ doping strategy using Cs₂WCl₆, a vacancy-ordered double perovskite, to achieve efficient NIR-II emission. Spectroscopic and dynamic measurements reveal energy transfer between the Cs₂WCl₆ matrix and the Re⁴⁺ centers, resulting in efficient broadband NIR-II emission centered at 1345 nm (FWHM ≈ 87 nm), along with broad excitation ranging from 250 to 850 nm. The optimal NIR-II emission occurs at 1345 nm with a photoluminescence quantum yield (PLQY) of 29.83% when the Re⁴⁺ doping concentration is 1%. This work demonstrates an efficient, sensitizer-free method for achieving broadband NIR-II emission and provides a new material strategy for high-performance double perovskites NIR light sources.