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.

Luminescent metal halide perovskites (MHPs) open new avenues for highly efficient radiation detection. To challenge the state‐of‐art technology, fundamental understanding of factors controlling radiation light yield of MHP scintillators is urgent. Herein, a design method is established by simultaneously considering charge‐transfer and recombination efficiencies via band alignment engineering in doped MHPs materials, and this strategy is corroborated experimentally and computationally by applying it to the luminescence of ns2 electron (Sb3+, Bi3+, and Te4+) doped vacancy‐ordered double perovskite Cs2ZrCl6. Alloying Te4+ into Cs2ZrCl6 is optimized and significantly improves the scintillation performance, including a twofold increase in light yield and a threefold increase in detection limit over pristine Cs2ZrCl6, and high‐resolution X‐ray imaging with 20 μm for 2D and 0.2 mm for 3D imaging. It is believed that doping engineering in MHPs enabling band alignment method holds great potential for the development of next‐generation MHP scintillators.

Yb 3+ doped lead-free double perovskites (DPs) with near-infrared (NIR)emitting have attracted extensive attention due to their wide application prospects. Unfortunately, they still suffer from weak NIR emission due to undesirable resonance energy transfer between the sensitizers and Yb 3+ ions. Herein, a new effective NIR-emitting DP is developed by co-doping Sb 3+ and Yb 3+ into Cs 2 AgInCl 6 . Experiments and theoretical calculations reveal that induced by co-doping Sb 3+ ions, the self-trapped excitation (STE) emission intensity of Cs 2 AgInCl 6 is greatly enhanced by 240 times, and the STE emission shifts from 600 nm to 660 nm, which contributes to a larger spectral overlap between STE emission and the absorption of Yb 3+ ions. As a result, the absolute NIR photoluminescence quantum yield reaches an unprecedented 50% in lead-free DPs via high-efficiency STE sensitization (>30%). The excellent optical performance of Cs 2 AgInCl 6 : Sb, Yb with high ambient, thermal and light stability makes it suitable for application in night-vision devices. Moreover, an ingenious dual-modal optical information encryption based on the combination of visible and NIR fluorescence printing patterns utilizing Cs 2 AgInCl 6 : Sb and Cs 2 AgInCl 6 : Sb, Yb respectively is successfully demonstrated. This study provides inspiration for designing highly efficient NIR-emitting Ln 3+ -doped DPs and illustrates their great potential in versatile optoelectronic applications.

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