The effects on optical and mechanical properties of introducing large amounts of TiO2 and Nb2O5 in a silicate matrix have been studied. Raman spectroscopy has been carried out in order to tentatively establish correlations between structural and physical properties. The high linear refractive index and the increase of the hardness for increasing d(0) ions concentration have been related to the formation of a denser glass network dominated by corner linked NbO6 and TiO6 octahedra. (C) 2012 Elsevier Ltd. All rights reserved.