Boosting NIR-II/III Luminescence via Fe3+-Ni2+ Energy Channels and Crystal Field Modulation in Monoclinic Double Perovskites

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.