Blue Upconversion Emission in Yb³⁺ and Tm³⁺ Codoped Lead-Germanate-Tellurite Glasses

Intense blue and red upconversion emissions have been observed in Yb³⁺/Tm³⁺ co-doped 0.05 K₂O-0.1ZnO-0.1BaO-0.2PbO-0.2GeO₂-0.35TeO₂ glasses under the pump of 976-nm laser diode. The dependence of the intensity of the upconversion emissions on the Tm³⁺ concentration has been studied in order to determine the ion concentration and the involved mechanism. The blue emission centred at 476 nm decreases and the 792-nm red emission increases with the increasing Tm³⁺ concentration. Subsequently, the dependence of upconversion emission intensity on the excitation power is investigated. It is found that the intensity ratio between the 792-nm red and 476-nm blue emissions decreases with the increasing pump energy.