(100- x ) SiO 2 – x SnO 2 ( x from 12 to 60 mol%) glass–ceramic thin films have been prepared by the sol–gel processing method, obtaining high SnO 2 concentrations (up to 60 mol%) for the first time. Using an appropriate thermal process, SnO 2 nanocrystals were nucleated in the glassy silica matrix, providing optical waveguides for x ≤ 30 mol%. M-line measurements were used to determine the thickness and refractive index of each film. Raman and FTIR spectroscopies, in situ high-temperature XRD and TEM data have been used to identify the initiation of crystallization (at about 900 °C for x ≤ 30 mol%). Calculations based on the low-wavenumber Raman data yield the sizes of the semi-conductor nanoparticles, which vary from 3.2 to 4.6 nm with heat-treatments varying from 900 °C to 1100 °C for SnO 2 concentrations varying from 12 to 30 mol%. Raman and FTIR data have provided information on the structural evolutions of the matrix which result from the formation and the growth of the SnO 2 nanocrystals.