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

Abstract

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.