Upconversion emissions in Yb3+–Tm3+-doped tellurite glasses excited at 976 nm

Intense Tm3+ blue upconversion emission has been observed in Tm3+–Yb3+ codoped oxyfluoride tellurite glass under excitation with a diode laser at 976 nm. Three emission bands centered at 475, 650 and 796 nm corresponding to the transitions 1G4→ 3H6, 1G4→ 3H4 and 3F4→ 3H6, respectively, simultaneously occur. The dependence of upconversion intensities on Tm3+ ions concentration and excitation power are investigated. For fixed Yb2O3 concentrations of 5.0 mol%, the maximum upconversion intensity was obtained with Tm2O3 concentration of about 0.1 mol%. The blue upconversion luminescence lifetimes of the Tm3+ transitions 1G4→ 3H6 are measured. The results are evaluated by the possible upconversion mechanisms.