Luminescence properties and spectral modulation of the ultra-broadband, highly efficient near-infrared luminescent material CaGa4O7:Cr3+, Cr4+, Yb3+

Recently, near-infrared phosphors have received a lot of attention due to their wide application in the field of detection and analysis, and it is urgent to develop efficient broadband NIR phosphors. In this paper, a conventional high-temperature solid-phase method was used to prepare a novel near-infrared phosphor CaGa4O7:Cr3+, Cr4+, which provides two emission bands ranging from 600 to 1000 nm and 1100–1600 nm. Although there are only four and five coordination sites in the CaGa4O7 (CGO) lattice, the doping of the Cr3+ ions in the CGO causes the Ga–O tetrahedral distortion into an octahedron, providing a favorable environment for the emission of the Cr3+ ions. Under blue light excitation, Cr3+ emits luminescence in the NIR I region from 600 to 1000 nm with a half-height width of up to 148 nm. With increasing Cr ion concentration, more and more Cr4+ preferentially occupy the four coordinated Ga3+ sites, and the intensity of the ultra-broad emission band in the NIR II region (1100 nm–1600 nm) increases with a full width at half maximum (FWHM) of 262 nm. To further optimize the emission spectrum, Yb3+ was codoped into CGO: Cr3+, Cr4+, the energy transfers from Cr3+ to Yb3+ in CGO was found, thus filling the gap between 1000 and 1100 nm in the CGO emission spectrum and obtaining a more complete ultra-wide spectrum. Moreover, the luminescence mechanism, energy transfer efficiency, and quantum yield are also studied in detail, and the ability of CaGa4O7:Cr3+, Cr4+, and Yb3+ luminescent materials to achieve ultra-broadband efficient near-infrared emission was demonstrated.