It is well known that pure tellurium oxide exhibits serious
restrictions to become glass [3,4]. Such difficulty is attributed to
the presence of a pair of electrons in the equatorial region of the
TeO4 trigonal bipyramidal (tbp) found in the tellurium oxide network
which limits the structural arrangement necessary for glass
formation. Thus, it is extremely difficult to obtain pure tellurium
oxide glass using the traditional melt-quenching method. On the
other hand, tellurite glass can easily be obtained by incorporating
an alkaline oxide as a net modifier. However, such incorporation
affects the optical properties, mainly the linear and non-linear
refractive indices. When the ratio of the modifying oxide increases,
the dominant TeO4 tbp progressively converts into TeO3 trigonal
pyramids (tp) [