Silver nanoparticles were synthesised in thin surface layers of SiO2 glass by 30 keV implantation of Ag+ ions with various fluences. Properties of the composites were studied using optical spectroscopy and atomic force microscopy. Optical spectra reveal specific absorption bands assigned to the surface plasmon resonance of the nucleated Ag nanoparticles. The spectral positions of absorption maxima are found to be dependent on the ion fluence that corresponds to difference in mean sizes of the nanoparticles. Microscopy study shows formation of hemispherical nanosize bumps on the glass surfaces which represent a near-surface fraction of the partly towered nanoparticles. Post-implantation annealing leads to shift of the plasmon maxima and to change of the band widths. The transformations of optical spectra are in good agreement with the change of nanoparticle sizes found by atomic force microscopy. Possible mechanisms governing the redistribution of the nanoparticles in size under the thermal treatment are suggested and discussed.