Abstract
Cr4+-activated phosphors are important candidate materials for NIR-II light sources, but providing a suitable lattice coordination environment for Cr4+ and achieving long wavelength broadband emission remains a challenge. In this work, a series of Cr4+-activated ABO2 (A = Li, Na; B = Al, Ga) phosphors were successfully prepared. Due to the presence of only tetrahedral coordination structures available for Cr4+ to occupy in the matrix crystal ABO2, the valence state and luminescence stability of Cr4+ are effectively guaranteed. Through the cation substitution design of A-site (Na → Li) and B-site (Ga → Al), the [BO4] tetrahedron is distorted and expanded, which degrades the symmetry of the Cr4+ coordination crystal field. Consequently, the central wavelength of the Cr4+ emission peak is tuned from 1280 to 1430 nm, and the fwhm is significantly extended from 257 to 355 nm. Thebroadband NIR-II light sources constructed with LiAlO2: 0.03Cr4+ and NaGaO2: 0.03Cr4+ phosphors verify their important potential applications in nondestructive testing and biological imaging.
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