Near-infrared Phosphors: Photophysical Properties of Calcium-doped YSGG:Cr4

Toward developing super-broadband LEDs using NIR phosphors, the effect of Ca substitution on the luminescence of Cr-doped Y3Sc2Ga3O12 garnet (YSGG) was evaluated. The valence of chromium ions in YSGG mainly takes two states, trivalent and tetravalent, and YSGG shows luminescence peaks at 740 nm (Cr3+) in octahedral Sc sites and at 1530 nm (Cr4+) in distorted tetrahedral Ga sites. The garnet host is very suitable for optical-sensing LED applications because these two emission bands closely match two NIR windows, NIR-I (600-950 nm) and NIR-III (1500-1800 nm), which are applied for bio-imaging. In this study, we demonstrated that the Cr4+ broad emission was improved by Ca substitution to control the photophysical properties. We concluded that YSGG:Cr4+ with D-2d symmetry in a unique distorted tetrahedron is a promising NIR phosphor for light-emitting applications.