Abstract: Er³⁺-doped tellurite glasses with various Na₂O/K₂O ratios were prepared by conventional glass
melting. Glass transition temperature T_g and crystallization temperature T_x were tested by DSC. The effect of mixed alkali on thermal
stability of tellurite glasses was described. The results show that the mixed alkali is beneficial to tellurite glasses on thermal stability and the best
mixed alkali molar ratio is Na₂O/K₂O=1/4. According to absorption spectra, Judd-Ofelt intensity parameters were determined and used to
calculate the radiation rates, fluorescent branch ratio and radiative lifetimes of Er3+ in tellurite glasses. The J-O parameters were
obtained, Ω₂=4.79×10^-20cm², Ω4=1.52×10^-20cm², Ω₆=0.70×10^-20cm². The stimulated emission cross sections
(σ_e=10.40×10^-21cm²) of the Er³⁺ ion ⁴I_13/2→⁴I_15/2 transition was calculated by the McCumber theory. The FWHM(FWHM=65.5nm) of the ⁴I_13/2→⁴I_15/2 emission and
lifetimes of every level of Er³⁺ ion were measured and the lifetime of ⁴I_13/2 level is 3.99ms. The spectroscopic properties of Er³⁺ ion
were compared in different glasses. The conclusions indicate that tellurite glass is much more beneficial for optical fiber amplifier to realize broadband
and high gain amplification.

Key words: tellurite glass, thermal stability, spectroscopic properties, Judd-Ofelt theory