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.