Boosting NIR‐II/III Luminescence via Fe 3+ ‐Ni 2+ Energy Channels and Crystal Field Modulation in Monoclinic Double Perovskites

ABSTRACT Blue‐light‐excitable near‐infrared (NIR) emitting materials exhibit significant potential for compact light sources in bioimaging, nondestructive detection, and night vision. However, achieving efficient NIR‐II/III (1000–1800 nm) emission under blue excitation remains challenging due to the large excitation–emission Stokes shift and the forbidden nature of f – f or d – d transitions. In this study, we report on the Ni 2 + ‐doped monoclinic double perovskite Ca 2 ScTaO 6 , which exhibits broadband NIR‐II/III with a full width at half maximum of 240 nm and a photoluminescence quantum yield of approximately 21% when excited at 425 nm. The incorporation of Fe 3+ ions significantly improves the photoluminescence quantum yield to approximately 37% through energy transfer pathways from Fe 3+ to Ni 2+ and crystal field modulation. Structural and spectroscopic investigations reveal the presence of Fe 3+ ions at various lattice sites, resulting in localized distortions that facilitate the relaxation of d – d transitions in Ni 2+ . A prototype NIR light‐emitting diode utilizing Ca 2 ScTaO 6 :Fe 3+ , Ni 2+ exhibits strong NIR‐II/III emission, facilitating the visualization of subsurface damage in various materials, including fruits, capsules, meat, and silicon wafers. This work demonstrates an effective strategy for designing blue‐light‐excitable NIR materials through synergistic energy transfer and crystal field engineering.