This article reports a study on the preparation, densification process, and structural and optical properties of SiO2-Ta2O5 nanocomposite films obtained by the sol-gel process. The films were doped with Er3+ and the Si:Ta molar ratio was 90:10. Values of refractive index, thickness and vibrational modes in terms of the number of layers and thermal annealing time are described for the films. The densification process is accompanied by OH group elimination, increase in the refractive index, and changes in film thickness. Full densification of the film is acquired after 90 min of annealing at 900 degrees C. The onset of crystallization and devitrification, with the growth of Ta2O5 nanocrystals occurs with film densification, evidenced by high-resolution transmission electron microscopy. The Er3+-doped nanocomposite annealed at 900 degrees C consists of Ta2O5 nanoparticles, with sizes around 2 nm, dispersed in the SiO2 amorphous phase. The main emission peak of the film is detected at around 1532 nm, which can be assigned to the I-4(13/2)-> I-4(15/2) transition of the Er3+ ions present in the nanocomposites. This band has a full width at half medium of 64 nm, and the lifetime measured for the I-4(13/2) levels is 5.4 ms, which is broader compared to those of other silicate systems. In conclusion, the films obtained in this work are excellent candidates for use as active planar waveguide. (C) 2010 Elsevier B.V. All rights reserved.