A Bifunctional Cr/Yb/Tm:Ca<sub>3</sub>Ga<sub>2</sub>Ge<sub>3</sub>O<sub>12</sub> 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 (Ca<sub>3</sub>Ga<sub>2</sub>Ge<sub>3</sub>O<sub>12</sub>) host where lanthanide ions such as Tm<sup>3+</sup>/Yb<sup>3+</sup> and transition metal ions such as Cr<sup>3+</sup> can be easily incorporated through substituting the Ca<sup>2+</sup> and Ga<sup>3+</sup> respectively. This Cr/Yb/Tm:Ca<sub>3</sub>Ga<sub>2</sub>Ge<sub>3</sub>O<sub>12</sub> phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr<sup>3+</sup> with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm<sup>3+</sup>. Impressively, it is evidenced that the addition of Yb<sup>3+</sup>/Tm<sup>3+</sup> into Cr:Ca<sub>3</sub>Ga<sub>2</sub>Ge<sub>3</sub>O<sub>12</sub> not only results in Tm<sup>3+</sup> upconversion luminescence but also greatly increases Cr<sup>3+</sup> 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.