Evidence for pair generation of anE’ center and a nonbridging oxygen-hole center in γ-ray-irradiated fluorine-doped low-OH synthetic silica glasses

We have examined effects of fluorine concentration on defect formation by \ensuremath{\gamma}-ray irradiation in low-OH synthetic silica glasses over the F concentration range 0--3 wt. %. Doping with 1 wt. % of fluorine eliminates effectively \ensuremath{\equiv}Si-Cl without causing formation of \ensuremath{\equiv}Si-Si\ensuremath{\equiv} and \ensuremath{\equiv}Si-H (all such structural units may be precursors of the E' center); and \ensuremath{\equiv}Si-F does not behave as the precursors of the E' center. At this doping level, the concentration of the E' center is minimized, and the concentration coincides with that of the nonbridging oxygen-hole center (NBOHC). We conclude that pair generation of the E' center and NBOHC from intrinsic \ensuremath{\equiv}Si-O-Si\ensuremath{\equiv} bonds is observed in the samples in which the precursor defects are suppressed by proper F doping.