Multiple Crystal-Fields Engineering in Spinel Unlocks Efficient Broadband NIR Emission of Cr3+

Achieving efficient ultra-broadband near-infrared (NIR) emission in Cr 3+ -doped traditional spinel remains a challenge owing to the inherent rigidity of the host lattice and the dominant strong crystal-field effect. Herein, we demonstrate multiple crystal-field engineering to realize efficient broadband NIR emission in Cr 3+ -activated spinel phosphors. A low-symmetry Mg 4 InSbO 8 spinel with mixed-cation octahedral sublattices is employed to construct diversified weak crystal-field environments for Cr 3+ . Through synergistic site and valence regulation, the occupation of Cr 3+ at various octahedral sites is optimized, while the unfavorable formation of high-valent Cr 4+ is suppressed. Specifically, partial Ga substitution in In/MgO 6 octahedra mitigates lattice mismatch and weakens electron-phonon coupling. Meanwhile, LiF acts as a flux agent and charges compensator under an N 2 atmosphere to further restrict Cr 4+ generation. The optimized phosphor exhibits a broadband NIR emission centered at 783 nm with a full width at half maximum of 203 nm and an internal quantum efficiency of 89.1%. The integrated emission intensity at 423 K remains 46.2% of the intensity at room temperature. The as-fabricated phosphor-converted light-emitting diode (pc-LED) enables clear target imaging at a distance of 2.7 m through dense smoke at night, outperforming a conventional visible pc-LED that achieves only an imaging distance of 0.4 m.