Optical absorption and photoluminescence of diacid tetraphenylprophyrine, H4TPP2+, species in silica gel glass prepared by the sol-gel (SG) method were measured in the 350-800 nm range. Under continuous (CW) laser excitation the characteristics of thermal lensing (TL) were measured at room temperature, under resonant and non-resonant conditions. Our results are analyzed based on a theoretical model for CW laser-induced thermal lensing, under a Gaussian-beam approximation. The effects of the power input and the response time for TL are explained in terms of the coupling of the H4TPP2+ molecules to the local vibrations, for resonant excitations. Also, the observation of laser-induced permanent changes in the refractive index of our glass sample under resonant and non-resonant excitations is reported and discussed. (C) 2002 Elsevier B.V. All rights reserved.