Ultra-broad NIR emission from two-site Cr3+occupation in fluoride phosphor via composition-driven structural transformation

Cr3+-activated fluoride-based near-infrared (NIR) phosphors have attracted wide attention from re-searchers due to their high luminous efficiency and high thermal stability. However, the practical application of this type of phosphors is severely hindered by their narrow emission. In this work, a structural transformation from Li3GaF6 to LiMgGaF6 was successfully obtained by stoichiometric control during hydrothermal process, leading to an NIR phosphor LiMgGaF6:Cr3+ with broadband emission ranging from 650 to 1150 nm. With the replacement of Li by Mg atom of Li3-2xMgxGaF6:Cr3+(0 <= x <= 1), the full width at half maximum of emission band can be broaden to 189.9 nm from 140 nm. This ultra -wide NIR emission of fluoride phosphor is caused by double-site Cr3+ occupation, which is verified by activator concentration-dependent spectra, Rietveld structural refinement, and density functional theory first-principles calculations. Despite the wide-band NIR emission, the LiMgGaF6:Cr3+ phosphor shows relatively high quantum efficiency of 42.3% and high thermal stability, which maintains 50% of its initial intensity at 400 K. The ultra-broadband NIR emission of LiMgGaF6:Cr3+ has potential applications as a light source in ingredient identification, and the strategy of multisite occupation of Cr3+ through compositional regulation opens a new way for the exploration of Cr3+-doped broadband NIR fluoride phosphors.(c) 2022 Elsevier Ltd. All rights reserved.