Optical responses of pristine Ag metal nanoparticles in a SiO2 matrix have changed drastically upon high-energy Si ion-irradiations. Systematic blueshifts of the quantum surface plasmon resonances and concomitant decrease in the optical absorption resonance intensities with increase of ion dose of Si ions are thought to be due to decrease in size of Ag nanoparticles. Observed shrinking of sizes of Ag metal nanoparticles due to irradiation effects of high-energy Si ions has been elucidated using model calculations. Transmission electron microscopy as well as Raman scattering spectroscopy confirms decrease in size of Ag nanoparticles caused by the Si ion-irradiations. (C) 2014 Elsevier B.V. All rights reserved.