Highly Efficient and Thermally Stable Ultra-Broadband\nNIR-II Emtting Li(Ga, Al)<sub>5</sub>O<sub>8</sub>:Cr<sup>3+</sup>, Ni<sup>2+</sup> Phosphors for Spectroscopy Analysis

Near-infrared\n(NIR) spectroscopy has diverse applications across\nvarious fields, such as the detection of food components and pesticide\nresidues, early diagnosis, and treatment of cancer. In this work,\na series of optimized LiAl<sub>5–<i>x</i></sub>Ga<sub><i>x</i></sub>O<sub>8</sub>:0.1Ni<sup>2+</sup> (<i>x</i> = 0–5) ultrabroadband NIR-II luminescent systems\nare developed. The density functional theory (DFT) calculations, time-resolved\nphotoluminescence (TRPL) spectroscopy, and 77 K PL spectra demonstrate\nthat the substitution of Ga<sup>3+</sup> for Al<sup>3+</sup> creates\nmore favorable sites for Ni<sup>2+</sup> luminescence and enhances\nstructural orderliness while reducing the number of luminescent centers.\nThis leads to a red shift in the emission peak from 1177 to 1252 nm\nwith a 14-fold increase in luminescence intensity. At 375 K, thermal\nstability increases from 81% (<i>x</i> = 0) to 90% (<i>x</i> = 5) compared to 300 K. Subsequent co-doping with Cr<sup>3+</sup> results in an excitation peak with a red shift into the\nblue-violet region (420 nm), accompanied by a notable enhancement\nin absorption efficiency (AE) and an increase in external quantum\nefficiency (EQE) from 4% to 62%. Finally, the potential application\nof the prepared phosphors in both qualitative and quantitative analysis\nof organic compounds is demonstrated, which will offer new insights\nfor the design and synthesis of ultrabroadband NIR-II light sources.