Analysis of down conversion and back-transfer processes in Pr3+-Yb3+ co-dopedphosphate glasses

The visible to near-infrared spectral modification in Pr3+ and Yb3+ co-doped phosphate glasses were verified through the energy transfer from Pr3+ to Yb3+ ions. A series of 0.1Pr(3+)-xYb(3+)(x = 0.5, 1, 1.2 mol%) co-doped phosphate glasses were prepared by the melt quenching method. The absorption, excitation and emission spectra and fluorescence decays were measured and analyzed. The emission in the visible region and the luminescence decay times of the Pr3+ confirmed the coexistence of the down-conversion processes from Pr3+ to Yb3+ due to the mechanism: Pr3+(D-1(2)) + Yb3+(F-2(7/2)) -> Pr3+(F-3(3)) + Yb3+(F-2(5/2)) and the cross relaxation processes between Pr3+ ions. The down conversion produces an important population of Yb3+ ions and consequently an intense emission at 975 nm. However, when the concentration of Yb3+ is larger than 0.5 mol% the emission from the Yb3+ start to decrease. In order to analyze all the transfer processes is proposed a generalized energy transfer model. Therefore, in basis to this model the luminescence decay curves of Yb3+ ions confirm an important back-transfer mechanism from these excited ions to the Pr3+ ions. This process limits the emission intensity of Yb3+ ions in the near-infrared region obtained by down-conversion under direct excitation of Pr3+ ions.

Automated summary

The energy transfer mechanism between Pr3+ and Yb3+ ions in co-doped phosphate glasses was investigated, and its impact on the emission intensity was analyzed.