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

We have examined effects of fluorine concentration on defect formation by -ray irradiation in low-OH synthetic silica glasses over the F concentration range 03 wt. %. Doping with 1 wt. % of fluorine eliminates effectively Si-Cl without causing formation of Si-Si and Si-H (all such structural units may be precursors of the E center); and 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 Si-O-Si bonds is observed in the samples in which the precursor defects are suppressed by proper F doping.