Highly stable glasses in the (70 − x)Sb2O320Na2O10ZnOxEr2O3 (x = 0.25, 0.5, and 1.0 mol%) system have been prepared and investigated by UV–Vis–NIR absorption, near infrared photoluminescence and time-resolved spectroscopy. Judd–Ofelt study has been used to determine the intensity parameters (Ω2, Ω4, and Ω6), spontaneous emission probabilities, branching ratios, and radiative lifetimes (τR) related to the corresponding optical transitions of Er3+ ions. Details of the emission at ∼1530 nm and spectroscopic characteristics such as the stimulated emission cross-section (σe), effectiveband width (Δλeff), quantum efficiency, and the optical gain have been summarized, accounting the role of the increased Er content. The obtained results indicate that these new low phonon energy glasses could be used as a laser medium and for optical amplification in the 1.5 µm region. In particular, the composition containing 0.5 mol% Er2O3 exhibits optimal values of Ω2 (4.5 × 10−20 cm2), Δλeff = 57 nm, σe = 7.28 × 10−21 cm2, τmeas (3.36 ms), and quantum efficiency of the 4I13/2 level of Er3+ ions ∼71%.