Cr³⁺/Ni²⁺ codoped LiGaSiO4: A thermally stable broadband NIR-II phosphor for non-invasive spectroscopic sensing of organic and aqueous systems

Near-infrared II (NIR-II, 1000–1700 nm) luminescent materials are essential for NIR spectroscopy applications, including biometrics, night vision imaging, and chemical composition analysis. However, achieving thermally stable and ultra-broadband emission under ultraviolet-to-visible (UV–Vis) excitation remains a significant challenge. In this work, a high-efficiency NIR-II phosphor was reported by codoping Cr³⁺ and Ni²⁺ ions into the LiGaSiO₄ lattice, where Cr³⁺ serves as a sensitizer and Ni²⁺ acts as the primary emitter. Owing to the strong absorption of Cr³⁺ in the violet region and its efficient energy transfer to Ni²⁺, the LiGaSiO₄:Cr³⁺/Ni²⁺ phosphor exhibits intense NIR-II emission under 419 nm excitation, with a peak centered at 1250 nm and a full width at half maximum (FWHM) of 227 nm. The material also demonstrates excellent thermal stability, retaining 73.3 % of its luminescence intensity at 393 K. Using a commercial 405 nm LED as the excitation source and a custom-engineered NIR-II spectroscopic detection platform, this phosphor enables functional group-specific differentiation of organic solvents and facilitates quantitative analysis of ethanol–water and NaCl–water binary systems across a broad concentration range. These findings highlight the potential of LiGaSiO₄:Cr 3+ /Ni 2+ as a robust NIR-II probe for next-generation portable sensing technologies, paving the way for the practical deployment of NIR-II photonics systems in industrial and biomedical applications.