Optical and spectroscopic properties of rare earth-doped (80−x)TeO2–xGeO2–10Nb2O5–10K2O glasses

Erbium-doped germanotellurite glasses in the TeO2–GeO2–Nb2O5–K2O system have been prepared and their absorption and photoluminescence properties were investigated. Judd–Ofelt theory was applied to the different absorption intensities of the UV/vis Er3+ transitions, to determine the intensity parameters, Ωt (t=2, 4, 6), and to estimate the radiative lifetimes. However, for a single transition like the Er3+ emission to the ground state, at ca. 1.5 μm, the absorption cross-section method is shown to be a simpler method to estimate the radiative lifetime of that particular transition. Experimental lifetimes were obtained from the photoluminescence decay curves of the 4I13/2 metastable state of Er3+ in different glasses and compared to the radiative lifetimes estimated by both methods. A better agreement was obtained by the absorption cross-section approach, yielding quantum efficiencies of 94% and 69% for 0.2 mol% and 2 mol% ErO1.5 doped samples, respectively. The up-conversion luminescence intensities of Er3+ ions in these glasses were also analyzed in the 400–900 nm range and compared with up-conversion in samples co-doped with Ytterbium and/or Thulium.