A Bifunctional Cr/Yb/Tm:Ca3Ga2Ge3O12 Phosphor with Near-Infrared Long-Lasting Phosphorescence and Upconversion Luminescence

Currently, upconversion nanocrystals and long-lasting phosphorescent particles have attracted extensive research interest for their possible applications as bioimaging probes. However, there are few reports concerning the achievement of both upconversion luminescence of lanthanide ions and long-lasting phosphorescence of transition metal ions in a sole host so far. Herein, we demonstrate a novel calcium gallium germanium garnet (Ca3Ga2Ge3O12) host where lanthanide ions such as Tm3+/Yb3+ and transition metal ions such as Cr3+ can be easily incorporated through substituting the Ca2+ and Ga3+ respectively. This Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr3+ with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm3+. Impressively, it is evidenced that the addition of Yb3+/Tm3+ into Cr:Ca3Ga2Ge3O12 not only results in Tm3+ upconversion luminescence but also greatly increases Cr3+ afterglow time. Based on excitation/emission, three-dimensional thermoluminescence, and time-resolved luminescence spectra, the related long-lasting phosphorescence and upconversion luminescent mechanisms are systematically discussed as well.