Effects of intrinsic defects on defect formation by excimer-laser irradiation were examined in synthetic silica glasses prepared by different methods. In samples containing oxygen-deficient centers (ODCs), laser-induced E centers were stable at room temperature. In contrast, in samples heat treated in H2 atmosphere, in which almost all ODCs changed into Si-H bonds, the induced-E- center concentration increased by about two orders of magnitude, and the resulting E centers were unstable, decaying at room temperature. We thus conclude that the formation efficiency of E centers from Si-H bonds is much higher than that of ODCs and that the induced-E centers recombine with radiolytic molecular H2 to restore Si-H bonds. It is suggested that a trace amount of Si-H bonds plays an essential role in defect creation and annihilation in OH-containing silica glasses.
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