Intense upconversion emission of Er3+/Yb3+-codoped Bi2O3-Ge2-Na2O glasses

Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth glasses for developing potential upconversion lasers have been fabricated and characterized. The absorption and upconversion fluorescence spectra were measured and investigated. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er³⁺ based on the Judd-Ofelt theory. Intense green and red emission bands at around 526, 547, and 657 nm wavelength were observed at room temperature. The mechanisms for explaining these upconversion processes have also been provided. The optimal rare earth doping ratio of Er³⁺ and Yb³⁺ is 1:6 for these glasses, which results in a stronger upconverssion fluorescence intensities. The upconversion efficiency was measured when the incident light power density was about 270W/cm², and the "standardized" upconversion efficiency for green emission is 2.27×10^-4. This value is higher than those reported in lead-germanate, lead-tellurite-germanate, and silicate glasses. The results indicate that the Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth oxide glass may be a potential material for developing upconversion optic devices.