Modifications of optical absorption band of Eγ′ center in silica

We report an experimental study of the modifications induced by gamma ray irradiation and by thermal treatment of both the electron paramagnetic resonance (EPR) and the optical absorption spectra of the Eγ′ center in silica. Our data show that the main g-values of Eγ′ EPR signal change as a function of the irradiation dose together with a red shift of the peak position of the absorption band around 5.8 eV attributed to the same center. Changes in the opposite direction are observed in both signals after thermal treatments. The peak position change of the optical absorption band is in quantitative agreement with the g-values shift. This strict correlation is evidence for the existence of a structural degree of freedom of the Eγ′ centers reflected by both EPR and optical measurements.