Small Stokes Shift Induced Highly Efficient and Thermally Stable Broadband Near‐Infrared Antimonite Double Perovskite Emitters for Spectroscopy Applications

Abstract The exploration of efficient broadband portable near‐infrared (NIR) light sources is crucial for next‐generation NIR spectroscopy‐based technologies. However, developing thermally stable and highly efficient NIR photonic materials exceeding 830 nm is met with limited success. Here, a series of broadband NIR phosphors with long‐wavelength emission (λ em > 830 nm) is designed by incorporating activator Cr 3+ ions into ALaMgSbO 6 (A = Ca, Sr) double perovskite matrices. Specifically, a cation site substitution strategy is proposed to reduce the Stokes shift of ALaMgSbO 6 :Cr 3+ (A = Ca, Sr), rendering these as‐prepared NIR phosphors possess excellent thermal resistance performance (89.80%@423 K) and high quantum efficiency (82.5%) simultaneously. Structural analyses, DFT calculations, and spectroscopy measurements revealed that Cr 3+ ions can occupy both [SbO 6 ] and [MgO 6 ] polyhedral sites but prefer to replace Sb 5+ ions in ALaMgSbO 6 (A = Ca, Sr). The luminescence efficiency and thermal stability of the samples are further improved through a flux strategy, and the emission spectra are effectively broadened by the introduction of Yb 3+ as an extra NIR emitter. Furthermore, the designed phosphors exhibit a full visible‐spectrum conversion ability from 400 to 800 nm, showing great promise for versatile NIR spectroscopy applications in solar energy harvesting, night vision, non‐destructive visualization, and dental analysis.