Polyethersulphone (PES) was irradiated with 4 MeV proton, 3.6 MeV C+, and 145 MeV Ne6+ ions at different ion fluences. The linear energy transfer dependence on ion-induced spectral changes was analyzed by ultraviolet-visible, Fourier transform infrared spectroscopy and fluorescence spectroscopy. The gradual red shift with the increase in optical absorption was observed in the region of 350-500 nm for proton and 400-800 nm for C+ and Ne6+ ions irradiated PES. The gradual shift in absorption may be attributed to the formation of carbonaceous clusters. The gradual decrease in optical band gap indicates increase in cluster sizes. When PES was irradiated with protons, loss in fluorescence emission intensity at 440 nm was observed, although there was no change in spectral shape. In contrast, C+ and Ne6+ ion irradiated PES showed blue shift with concomitant loss in intensity and the formation of new peak at 575 nm. In fact, heavier ions are found to be more effective in inducing physicochemical modifications in PES. (c) 2006 Wiley Periodicals, Inc.