Dense electronic excitation induced defects in fused silica

Investigation of defects created in optical grade fused silica due to 200 MeV silver ion irradiation is reported. Paramagnetically positively charged oxygen vacancies or neutral dangling Si bonds (E' centres), non-bridging oxygen hole centres (NBOHC) and non-paramagnetic defects like B2 bands are observed. The fluence dependent optical and paramagnetic behaviours of these defects are studied using UV-visible absorption spectroscopy, photoluminescence spectroscopy, infrared (IR) absorption and electron paramagnetic resonance. It is observed that generation of E' centres, NBOHC and B2 bands gets saturated beyond a fluence of 1 x 1012 ions cm-2. IR spectra showing saturation in transmission at this fluence also support this observation. At this fluence samples get fully covered with latent tracks containing these defects.