We present results of the study of optical and thermo-optical properties as well as the thermo-gravimetric analysis of SiO2:Er3+ (5% mol) glasses prepared by the sol-gel method at different pH (2, 3, 4 and 5). The thermo-optical characteristics were measured at room temperature under resonant conditions for the Er3+ ions and analyzed in terms of a theoretical model for continuum wave (CW) laser induced thermal lensing under a Gaussian-beam approximation. The thermo-optical properties showed a dependence on the pH conditions during the synthesis of the SiO2:Er3+ (5% mol.) glasses. © 2011 Academic Journals.