A cooperative afterglow enhancement in the second biological window of Na2CaSn2Ge3O12 with co-doping of Pr3+–Yb3+

Abstract

A novel near-infrared persistent luminescent phosphor Na₂CaSn₂Ge₃O₁₂ (NCSGO) doped with Ho³⁺, Er³⁺, Tm³⁺ and Yb³⁺ was synthesized by a high-temperature solid-state reaction. The afterglow emission bands located at 1553 nm, 801 nm and 970 nm were attributed to the transitions of ⁴I_13/2 → ⁴I_15/2 of Er³⁺, ³H₆ → ³H₄ of Tm³⁺, and ²F_5/2 → ²F_7/2 of Yb³⁺, respectively. Compared with single-doped afterglow, the co-doping of Pr³⁺ and Yb³⁺ not only increases the initial afterglow intensity of Pr³⁺ (2 times that of the Pr³⁺ single-doped sample), but also increases the initial afterglow intensity of Yb³⁺ (2.4 times that of the Yb³⁺ single-doped sample). At the same time, the associated afterglow duration is significantly prolonged. The persistent energy transfer (PET) between Pr³⁺ (∼607 nm) and Yb³⁺ (∼970 nm) was also confirmed. The calculation results of the luminescence decay curves showed that the energy transfer (ET) efficiency was 36%. The 3D thermoluminescence spectra of the samples were recorded, and a new model of the afterglow mechanism involving charge capture and the PET process was proposed.