Upconversion emissions in Yb 3+ –Tm 3+ -doped tellurite glasses excited at 976 nm

Intense Tm 3+ blue upconversion emission has been observed in Tm 3+ –Yb 3+ 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 1 G 4 → 3 H 6 , 1 G 4 → 3 H 4 and 3 F 4 → 3 H 6 , respectively, simultaneously occur. The dependence of upconversion intensities on Tm 3+ ions concentration and excitation power are investigated. For fixed Yb 2 O 3 concentrations of 5.0 mol%, the maximum upconversion intensity was obtained with Tm 2 O 3 concentration of about 0.1 mol%. The blue upconversion luminescence lifetimes of the Tm 3+ transitions 1 G 4 → 3 H 6 are measured. The results are evaluated by the possible upconversion mechanisms.