Highly Stable Lead‐Free Perovskite Single Crystals with NIR Emission Beyond 1100 nm

Materials that emit in the near‐infrared (NIR) region are at the forefront of both research and industry, mainly due to their wide applications in national security, nondestructive bioimaging, long‐wave communications, and photothermal conversion for medical care. As a key member of the luminescent materials family, metal halide perovskites have been intensively demonstrated to emit light in ultraviolet and visible regions. However, NIR‐emitting perovskites suffer from severe limitations, such as low photoluminescence quantum yield and poor chemical/optical stability, thereby preventing them from practical applications. Herein, the synthesis and growth of Cs2MoCl6 and Cs2WCl6 perovskite single crystals with ultrahigh chemical and optical resistance to heat, moisture, polar solvents, and high‐energy radiation is reported. Upon ultraviolet or blue excitation, these lead‐free single crystals emit light beyond 1100 nm, the longest wavelength ever reported for perovskite hosts. Mechanistic studies indicate that self‐trapped excitons are responsible for the NIR emission. The authors fabricate optoelectronic devices using these single crystals and demonstrate their broad applications in noninvasive palm vein imaging, night vision, and nondestructive food analysis. These results may stimulate research in the development of high‐efficiency NIR perovskite phosphors for fast, accurate biometric identification and food inspection. Two types of lead‐free halide perovskite single crystals that emit near‐infrared (NIR) light are developed. Experimental and theoretical characterization suggest that self‐trapped excitons are responsible for the observed large Stokes shift. These highly stable single crystals enable practical uses of NIR light emitting diodes for facile biometric authentication, night vision, and nondestructive food analysis.