Design and Control of the Luminescence of Cr3+-Doped Phosphors in the Near-Infrared I Region by Fitting the Crystal Field

Red or near-infrared phosphors, which have a lower absorption in biological tissue, show excellent promise in the field of bioimaging. Here, we design the red phosphor with a broad emission band and realize tunable luminescence of Cr3+ by two methods, i.e., adjusting the Cr3+-doping concentration in Zn3(AlGa)2­Ge2O10 solid solution and doping In3+ ions in Zn3Al2Ge2O10 due to a size mismatch. The solid solution is illustrated by density functional theory calculation, X-ray powder diffraction, and high resolution transmission electron microscopy. The Cr3+-doped phosphor shows a red emission band centered at 705 nm, which is ascribed to the 2E → 4A2 and 4T2(4F) → 4A2 transitions. When Cr3+ ions or In3+ ions are introduced, the full width at half-maximum (fwhm) increased due to the combination of crystal field splitting, nephelauxetic effect, and reabsorption.