The impact of different sodium concentrations on the thermal properties and near-infrared emission at 1540 nm of Er3+-doped tellurite glasses was investigated. The glasses were characterized by UV-visible-near-infrared absorption spectroscopy, emission spectroscopy, Raman spectroscopy, refractive index measurements, and lifetime estimates. A theoretical analysis of the prepared samples was performed with the Judd-Ofelt parameters, radiative transition probability, quantum yield, and radiative lifetime. The glasses presented a large calculated emission cross-section at around 1537 nm (8.4×10-21 cm2) and a good quantum yield (93%). The spectroscopic quality factors (Ω4/Ω6) obtained for the samples showed good agreement with the emission spectrum and bandwidth in the near-infrared region. The advantageous spectroscopic characteristics, together with good thermal stability, indicate that the glasses have potential applications as 1540 nm waveguides.