Broadband Near‐Infrared Emitting Lead‐Free Perovskites with High Internal Quantum Efficiency and Small Stokes Shift for Versatile Spectroscopy Applications

Abstract Materials capable of broadband near‐infrared (NIR) emission are critical for developing next‐generation intelligent NIR light sources based on phosphor‐converted light‐emitting diodes. However, the low quantum efficiency and poor thermal stability of most known broadband NIR‐emitting materials have limited their practical applications. Herein, this work presents an investigation of Mo 4+ ‐doped Rb 2 HfCl 6 lead‐free perovskite single crystals exhibiting broadband NIR emission with an exceptionally high internal quantum efficiency of 94.9% and a small stokes shift of 0.3 eV. Theoretical calculations, in parallel with experimental characterizations, are utilized to reveal that the intense NIR emission originates from the dopant‐induced extrinsic crystal field transitions, providing key insights into the underlying optical transition mechanisms. Notably, the relative intensity of these crystal field transitions gradually increases with increasing temperature. The NIR integrated intensity at 450 K remains 51% of that at 300 K under 746 nm red light excitation, while it is 40% under 298 nm UV light excitation. The intense broadband NIR‐emitting crystals demonstrate significant potential for nondestructive testing and spectroscopy applications. This work expands the repertoire of NIR light sources with high‐performance broadband NIR emission and opens new avenues for advanced spectroscopic technologies.