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, STH ₁ and STH ₂ 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 STH ₁ is about 4 times longer than that for STH ₂. Furthermore, the separated STH ₁ and STH ₂ signals have been experimentally obtained for the first time on the basis of the different decay times for each of two kinds of STHs.