Broadband Near‐Infrared Emission in Cr ³⁺ ‐Activated Ca ₂ LuGa ₃ Si _{2 Di Wu, Weiwei Zhu, Qi Wang, Zhiling Guo, Xinyue Yang, Xin Chen, Zhangwen Long, Dacheng Zhou, Jingchang Lin, Tao Han, Jianbei Qiu}

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.