Amorphous GexS1-x films (x = 0.27, 0.32, 0.36 and 0.4) were prepared by thermal evaporation. The values of the refractive index, the optical gap and the parameters of the Wemple-DiDomenico single oscillator model were determined. Using Miller's generalized rule the values of the third-order non-linear susceptibility were also estimated. Thermally induced bleaching was observed for films studied. Photobleaching was observed for sulfur rich and nearly stoichiometric films (x = 0.27, 0.32) while for a germanium rich film (x = 0.4) no response to the illumination was observed. The differences in photobleaching are attributed to the role of p-lone pair states and to an overall network rigidity of the films. (C) 2002 Elsevier Science B.V. All rights reserved.