Erbium-doped tellurite-based glasses (Er³⁺:TeO₂-ZnO-La₂O₃) are prepared by the conventional melt-quenching technique, and concentration-dependent luminescence properties of Er³⁺ are investigated. A significant spectral broadening of the 1.53 μm fluorescence corresponding to ⁴I_13/2 →⁴I_15/2 transition is observed, and the fluorescence decaying becomes a nearly exponential way with the increasing Er³⁺ concentration. Radiation trapping is evoked to explain the broadening of ⁴I_13/2 →⁴I_15/2 emission line of Er³⁺ ions. The optimum doping content of Er₂O₃ for 1.53 μm fluorescence emission is about 1.5 mol%.