Efficient Broadband Near‐Infrared Emission from Lead‐Free Halide Double Perovskite Single Crystal

Ultra‐broadband near‐infrared (NIR) luminescent materials are the most important component of NIR light‐emitting devices (LED) and are crucial for their performance in sensing applications. A major challenge is to design novel NIR luminescent materials to replace the traditional Cr3+‐doped systems. We report an all‐inorganic bismuth halide perovskite Cs2AgBiCl6 single crystal that achieves efficient broadband NIR emission by introducing Na ions. Experiments and density functional theory (DFT) calculations show that the NIR emission originates from self‐trapped excitons (STE) emission, which can be enhanced by weakening the strong coupling between electrons and phonons. The high photoluminescence quantum efficiency (PLQY) of 51 %, the extensive full width at half maximum (FWHM) of 270 nm and the stability provide advantages as a NIR luminescent material. The single‐crystal‐based NIR LED demonstrated its potential applications in NIR spectral detection as well as night vision. An all‐inorganic bismuth halide perovskite Cs2AgBiCl6 single crystal achieves efficient broadband NIR emission by introducing Na ions. Experiments and DFT calculations show that the emission originates from self‐trapped excitons emission. The role of Na is to weaken the strong coupling between electrons and phonons and to localize the electron and hole wave functions to enhance this emission.