Multiple Crystal‐Fields Engineering in Spinel Unlocks Efficient Broadband NIR Emission of Cr 3+

ABSTRACT 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.