Raman investigation and glass-compositional dependence on blue up-conversion photoluminescence for Tm3+/Yb3+ co-doped TeO2-TlO0.5-ZnO glasses
Résumé
In this study, glass-compositional dependence of Tm3+ blue up-conversion photoluminescence (UCPL), which is known to be obtained via three-steps' energy transfers from Yb3+ to Tm3+ ions under near-infrared light excitation at ~980 nm, is investigated for Tm3+/Yb3+ co-doped TeO2-TlO0.5-ZnO glasses. The third step of energy transfer from Yb3+ to Tm3+ ions is particularly important ((Yb3+, Tm3+); (2F5/2, 3H4)→(2F7/2, 1G4)) since it determines the final blue UCPL intensity from 1G4 level compared to red and near-infrared UCPLs, and so then estimated with varied TlO0.5 and ZnO contents at the expense of TeO2 in the fixed Tm3+ and Yb3+ contents ([Yb3+]/[Tm3+] = 5). The substantial energy transfer rate (ETR) in the third step is evaluated from excitation power dependence of the blue UCPL intensity in comparison with near-infrared UCPL of Tm3+ ions with an aid of analytical method of PL lifetime and Judd-Ofelt theory. It is here revealed that the highest ETR is achieved to be 3.54 × 10−17 cm3/s for the glass composition of 70TeO2-10TlO0.5-19.4ZnO-0.1Tm2O3-0.5Yb2O3, and that the transfer rate is possibly related with the length of TeO2 glass network because a long tellurite glass network can cause segregation of rare-earth elements inducing effective Yb3+-Yb3+ energy migration and less quenching centers like dangling bonds of isolated TeO32-, resulted in the enhancement of the energy transfer for blue UCPL.