Observation of defect formation process in silica glasses under ion irradiation

We have performed in situ measurements of luminescence from silica glass induced by H⁺ beam at various energies to investigate the dynamic defect formation process in a silica glass. The luminescence spectra showed a broad emission band centered at around 2.7 eV assigned to B_2α oxygen deficient centers. The intensity of the 2.7 eV band rapidly increased to H⁺ fluence at first, and then gradually increased to a steady value. We found that the change in the intensity of the 2.7 eV band relates to two processes, fast and slow processes with different reaction rates for producing luminescence centers. The dependences of calculated reaction rates for faster and slower transformation versus H⁺ energy correspond well to those of electronic and nuclear stopping power, respectively. Consequently, the production of the luminescence centers under sub-MeV H⁺ irradiation is very likely dominated by electron excitation process at first, and subsequently, by nuclear collision process.