Detection of Up-converted Persistent Luminescence in the Near Infrared Emitted by the Zn3Ga2GeO8: Cr3+, Yb3+, Er3+ Phosphor

Up-conversion luminescence and long-persistent luminescence are two well-studied, special luminescence processes. By combining the unique features of these two luminescence processes, here we design a new luminescence process called up-converted persistent luminescence (UCPL), which enables us to generate persistent luminescence having an emission energy higher than the excitation energy. Guided by the UCPL concept, we create the first UCPL phosphor Zn3Ga2GeO8 : 1% Cr3+, 5% Yb3+, 0.5% Er3+ by incorporating an up-converting ion pair Yb3+/Er3+ into a Zn3Ga2GeO8 : 1% Cr3+ near-infrared persistent phosphor. After being excited by a 980 nm laser, the phosphor emits long-lasting (> 24 h) near-infrared persistent emission peaking at 700 nm. The UCPL concept and the associated phosphors are expected to have important implications for several fields such as biomedical imaging.