Stability of E′ centers induced by 4.7 eV laser radiation in SiO2

The kinetics of E′ centers ( Si) induced by 4.7 eV pulsed laser irradiation in dry fused silica was investigated by in situ optical absorption spectroscopy. The stability of the defects, conditioned by reaction with mobile hydrogen of radiolytic origin, is discussed and compared to results of similar experiments performed on wet fused silica. A portion of E′ centers and hydrogen are most likely generated by laser-induced breaking of Si–H precursors, while an additional fraction of the paramagnetic centers arise from another formation mechanism. Both typologies of E′ centers participate in the reaction with H2 leading to the post-irradiation decay of the defects. This annealing process is slowed down on decreasing temperature and is frozen at T = 200 K, consistently with the diffusion properties of H2 in silica.