Powerful visible upconversion fluorescence of Er³⁺ in novel bismuth gallate glasses compared with in common tellurite glasses

Powerful visible upconversion fluorescence intensities of Er³⁺ in novel bismuth gallate glasses (LKBBG) and common tellurite glasses (TZN) with low phonon energies and high refractive indices have been compared. Under the same measurement condition, Er³⁺-doped LKBBG glasses show the stronger upconversion emission intensities than Er³⁺-doped common tellurite glasses (TZN). The visible upconversion emission bands peaked at 531, 548 and 668 nm have been confirmed that two photons contribute to these upconversion processes. The maximum phonon energy obtained in LKBBG glasses is 673 cm^-1, which is 65 cm^-1 lower than that in common tellurite glasses, indicating that LKBBG glasses almost possess the lowest maximum phonon energy in all of the oxide glasses. All analyses support that Er³⁺-doped LKBBG glasses are promising materials for fabricating visible upconversion devices.