IR and UV spectral studies for rare earths-doped tellurite glasses

Infrared absorption spectra were measured for pure TeO2 glasses and doped with 10-wt% of different rare-earth oxides, La2O3, CeO2, Pr2O3, Sm2O3, Nd2O3, and Yb2O3. The recorded bands were attributed to the different modes of vibrations of Te–O band. Rare earths connected to the chains of TeO4 groups are identified on the basis of the simultaneous presence of the bands at ∼660 to 625 cm−1. Quantitative justification of these absorption bands shows that the values of the experimental wave number for most recorded absorption bands agree well with the theoretical ones. Optical absorption spectra show that the absorption edge has a tail extending towards lower energies. The edge shifts towards higher energies for all rare earths-doped glasses. The degree of the edge shift was found to be depending on the ionic radius of the rare earths and is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. By increasing the ionic radius of the rare earths, the optical energy gap decreases, while the width of the localized states is increased.