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 Cr 3+ by two methods, i.e., adjusting the Cr 3+ -doping concentration in Zn 3 (AlGa) 2 Ge 2 O 10 solid solution and doping In 3+ ions in Zn 3 Al 2 Ge 2 O 10 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 Cr 3+ -doped phosphor shows a red emission band centered at 705 nm, which is ascribed to the 2 E → 4 A 2 and 4 T 2 ( 4 F) → 4 A 2 transitions. When Cr 3+ ions or In 3+ ions are introduced, the full width at half-maximum (fwhm) increased due to the combination of crystal field splitting, nephelauxetic effect, and reabsorption.