Highly Efficient and Thermally Stable Ultra-Broadband NIR-II Emtting Li(Ga, Al)5O8:Cr3+, Ni2+ Phosphors for Spectroscopy Analysis

Near-infrared (NIR) spectroscopy has diverse applications across various fields, such as the detection of food components and pesticide residues, early diagnosis, and treatment of cancer. In this work, a series of optimized LiAl_5–xGa_xO₈:0.1Ni²⁺ (x = 0–5) ultrabroadband NIR-II luminescent systems are developed. The density functional theory (DFT) calculations, time-resolved photoluminescence (TRPL) spectroscopy, and 77 K PL spectra demonstrate that the substitution of Ga³⁺ for Al³⁺ creates more favorable sites for Ni²⁺ luminescence and enhances structural orderliness while reducing the number of luminescent centers. This leads to a red shift in the emission peak from 1177 to 1252 nm with a 14-fold increase in luminescence intensity. At 375 K, thermal stability increases from 81% (x = 0) to 90% (x = 5) compared to 300 K. Subsequent co-doping with Cr³⁺ results in an excitation peak with a red shift into the blue-violet region (420 nm), accompanied by a notable enhancement in absorption efficiency (AE) and an increase in external quantum efficiency (EQE) from 4% to 62%. Finally, the potential application of the prepared phosphors in both qualitative and quantitative analysis of organic compounds is demonstrated, which will offer new insights for the design and synthesis of ultrabroadband NIR-II light sources.