Quantum cutting and up-conversion investigations in Pr3+/Yb3+ co-doped oxyfluoro-tellurite glasses

In this work we have investigated quantum cutting, up-conversion and downconversion processes in new Pr3+/Yb3+ co-doped transparent oxyfluoro-tellurite glasses with chemical composition TeO2-ZnO-YF3-NaF-0.5Pr(2)O(3)-xYb(2)O(3) (x = 0.25, 0.5, 0.75 and 1.0 mol%). In the down-conversion process, Pr3+-Yb3+ co-doped samples present emission in the visible (Pr3+: P-3(0) -> F-3(2) transition, 640 nm) and in the infrared (Yb3+:F-2(5/2) -> F-2(712), 980 nm) spectral regions upon excitation at 440 nm. The luminescence decay time of the emitting levels were obtained in co-doped samples as a function of Yb3+ concentration and the results confirmed the occurrence of energy transfer from Pr3+ to Yb3+ via a combination of two different cross relaxation processes: (1) Pr3+: P-3(0) -> (1)G(4) to Yb3+: F-2(7/2) -> F-2(5/2) and (2) Pr3+: D-1(2) -> F-3(4) to Yb3+: F-2(7/2) -> F-2(5/2). Furthermore due to the reverse-energy transfer mechanism from Yb3+ F-2(5/2) level to- Pr3+ (1)G(4) level, luminescence intensity quenching was observed for the F-2(5/2) -> F-2(7/2) transition at 980 nm, for Yb3+ concentrations higher than 0.5 mol%. The energy transfer efficiency was estimated from the intensity ratios and decay times associated to the P-3(0) -> F-3(2) transition, and it reached 66% for a glass co-doped with 0.5Pr(3+) and 1.0Yb(3+) (mol%). The results indicate that these glasses are potential candidates for manipulation of the solar spectrum, via up-conversion and downconversion processes, in order to increase the absorption efficiency of currently used c-Si photovoltaic solar cells. (C) 2016 Elsevier B.V. All rights reserved.