The influence of different Germanium dioxide concentration on the structural, thermal, optical and spectroscopic properties of Er3+ doped tellurite glasses was carefully investigated. The glasses were prepared by melt-quenching technique. The samples were characterized by UV–visible–near-infrared spectroscopy, downshift emission spectroscopy, Raman spectroscopy, lifetime of green emission and up-conversion under near-infrared laser diode excitation at 975 nm. The Judd-Ofelt analysis was performed based on the absorption spectra of the glasses in order to obtain the Judd-Ofelt parameters (Ωλ), radiative transition rates, radiative lifetimes and quantum efficiency. The solubility of Er3+ into the host vitreous matrix, the enhancement in the luminescence intensity and improvement in the thermal stability (≥ 100 ∘C) of the glasses was verified on introducing GeO2.