Abstract: The absorption spectra and upconversion luminescence spectra of Er³⁺-doped oxyfluoride tellurite
glasses were investigated, and upconversion luminescence mechanisms of Er³⁺ in oxyfluoride tellurite glasses were analyzed. The results
show that the intense green (524 and 545nm) and red (655nm) emissions corresponding to the ²H_9/2→⁴I_15/2, ²H_11/2→⁴I_15/2,
⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺ ions, respectively, can be simultaneously observed at room temperature under 975 nm diode laser excitation. With increasing PbF₂ concentrations, the intensity for the green emissions increases
slightly, while the red emission intensity enhances much larger than the green emission intensities. There are two basic upconversion mechanisms: excited state absorption and energy transfer, and a two-photon upconversion process is assigned to the intense green and
red emission, respectively.

Key words: oxyfluoride tellurite glass, spectral properties, upconversion luminescence, Er³⁺ ion