Raman scattering, dierential scanning calorimetry and Nd 3 spectroscopy in alkali niobium tellurite glasses Fabia C. Cassanjes a, * , Younes Messaddeq a , Luiz F.C. de Oliveira b , Lilia C. Courrol c , La ercio Gomes c , Sidney J.L. Ribeiro a a Instituto de Qu  õmica±UNESP, P.O. Box 355, Zip 14801-970, Araraquara, SP, Brazil b Departamento Qu  õmica, Universidade Federal de Juiz de Fora, Juiz de Fora, MG, Brazil c Instituto de Pesquisas Energ eticas e Nucleares±IPEN/CNEN, S~ ao Paulo, SP, Brazil Abstract Alkali niobium tellurite glasses have been prepared and some of their properties measured by dierential scanning calorimetry and Raman scattering. The vitreous domain was established in the pseudo ternary phases diagram for the system TeO 2 ±Nb 2 O 5 ±(0.5K 2 O±0.5Li 2 O). Raman scattering shows that for samples in the TeO 2 rich part of the phase diagram the vitreous structure is composed essentially of (TeO 4 ) units connected by the vertices, as in the a-TeO 2 crystal. The addition of alkali and niobium oxides causes depolymerization to occur with structures composed es- sentially of (TeO 3 ) and (NbO 6 ) units. Samples with the composition (mol%) 80TeO 2 ±10Nb 2 O 5 ±5K 2 O±5Li 2 O, stable against crystallization, were prepared containing up to 10% mol Nd 3 . The addition of this oxide increases the rigidity of the vitreous network shifting characteristic temperatures to higher temperatures. For the 10% Nd 3 sample amor- phous phase separation is assumed to exist from the observation of two glass transition temperatures. Spectroscopic properties such as Judd±Ofelt X k intensity parameters, radiative emission probabilities, and induced emission cross sections were calculated. From these results and also from the emission quenching observed as a function of Nd 3 concentration, we suggest that these glasses could be utilized in optical amplifying devices. Ó 1999 Elsevier Science B.V. All rights reserved. 1. Introduction Tellurite glasses have scienti®c and technologi- cal interest due to their relatively higher refractive indices and dielectric constants and lower phonon energies compared for instance with the well known silicate or phosphate glasses. The refractive indices allow the utilization of these glasses for non-linear optical materials [1] and the phonon energies have at least two important consequences ± improved infrared (IR) transmission (up to 6 lm) and low multiphonon decay rates for rare earths excited states as compared to silicate and phosphate glasses. Tellurite glasses are therefore potential candidates for IR transmitting devices and also hosts for IR emitting rare earths [2]. In a previous study we presented results on glass formation with the system TeO 2 ±Nb 2 O 5 ± Li 2 O±K 2 O [3]. A range of compositions may be obtained as stable glasses and in this work we present results on structural information obtained from Raman scattering spectra. Dierential scan- ning calorimetry (DSC) data and the spectroscopic Journal of Non-Crystalline Solids 247 (1999) 58±63 * Corresponding author. Tel.: +55-16 232 2022; fax: +55-16 222 7932; e-mail: fabiacc@iq.unesp.br 0022-3093/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 0 9 3 ( 9 9 ) 0 0 0 7 4 - 5