Photo-bleaching of self-trapped holes in SiO2 glass

Photo-induced bleaching of self-trapped holes (STH) in UV-irradiated synthetic silica has been investigated by the electron spin resonance method. We have observed two kinds of STH, STH1 and STH2 as assigned by Griscom in Ref. [D.L. Griscom, Phys. Rev. B 40 (1989) 4224]. The decay of all the spectral features was found to follow a stretched exponential function; and those features with the similar decay behavior were assigned to the same defect. The decay time obtained from the averaged fitting value for STH1 is about 4 times longer than that for STH2. Furthermore, the separated STH1 and STH2 signals have been experimentally obtained for the first time on the basis of the different decay times for each of two kinds of STHs.