Broadband Near‐Infrared Emission in Cr 3+ ‐Activated Ca 2 LuGa 3 Si 2 O 12 Garnet through Host‐Lattice Heterogeneity and Bi 3+ ‐Assisted Dual Regulation

ABSTRACT Broadband near‐infrared (NIR) phosphors with efficient excitation and high thermal stability are highly desirable for spectroscopy, nondestructive inspection, and night‐vision imaging. However, in Cr 3+ ‐activated garnets, these properties are rarely achieved simultaneously because a strong crystal field generally leads to narrowband emission. Here, we report a new silicate garnet, Ca 2 LuGa 3 Si 2 O 12 (CLGS), constructed from the Lu 3 Ga 5 O 12 prototype via coupled Ca 2+ ‐Si 4+ and Lu 3+ ‐Ga 3+ substitution. This strategy creates a chemically heterogeneous lattice with distributed local cation environments. Under visible‐light excitation, CLGS: 10%Cr 3+ exhibits broadband NIR emission centered at 800 nm with a full width at half maximum of 170 nm, despite an average strong crystal field (Dq/B = 2.51). Such unusual behavior is attributed to substitution‐induced local crystal‐field distribution, multiple Cr 3+ ‐related emitting environments, and possible thermally assisted population of the 4 T 2 state. Furthermore, Bi 3+ co‐doping enhances the NIR emission and thermal stability through ultraviolet sensitization and local crystal‐field modulation. The optimized composition is CLGS:10%Cr 3+ ,3%Bi 3+ , corresponding to the nominal formula Ca 2 Lu 0.97 Bi 0.03 Ga 2.9 Cr 0.1 Si 2 O 12 . A prototype NIR pc‐LED demonstrates the potential of the optimized phosphor for solvent discrimination and night‐vision imaging.