Upconversion luminescence of Er³⁺ in alkali bismuth gallate glasses

Frequency upconversion of Er³⁺ in alkali bismuth gallate glasses have been investigated. The upconversion mechanisms are discussed, and the dominant mechanisms are excited state absorption for the ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions, and energy transfer upconversion for the ⁴F_9/2 →⁴I_15/2 transition. Intense green (around 525-550 nm) and red (around 660 nm) emission bands were observed under 800 nm excitation. At a pump intensity of 15.6 W/cm², frequency upconversion efficiencies of 2.1×10^-2 and 4.8×10^-3 were obtained for the green and red emissions, respectively. The results are the highest among doped oxide glasses, and are comparable to those reported for Er³⁺/Yb³⁺ codoped fluoride glasses.