Persistence luminescence in Ca2Ge7O16:Pr3+ phosphors with visible and near-infrared emission

Ca_2-xGe₇O₁₆:Pr³⁺ (x = 0.125-1 mol%) phosphors were synthesized via the solid-state reaction at 1100 °C for 10 h. The Ca₂Ge₇O₁₆ tetragonal structure was identified in all samples. Photoluminescence emission spectra under 254 nm exhibited characteristic Pr³⁺ emission in visible (488, 566, 611, 634, 700, and 733 nm; corresponding to the ³P₀ → ³H₄, ³P₁ → ³H₅, ¹D₂ → ³H₄, and ³P₀ → ³F₂, ³F₃, ³F₄ transitions, respectively) and infrared region (979, 1059, and 1432 nm; corresponding to the ¹D₂ → ³F₃, ³F₄, ¹G₄ transitions, respectively) (Fig. 1A)^[1,2] with persistent luminescence emission at 611 nm (Fig. 1C) and 1059 nm (Fig. 1B) after 5 min. Afterglow emission remained detectable for at least 75 s in samples doped with up to 0.5 mol% Pr³⁺ (Fig. 1D). These results demonstrate that Ca₂Ge₇O₁₆:Pr³⁺ exhibits structural and spectroscopic properties, highlighting its potential for photonic device applications.