The formation of Ge electron centers in [SiO2]9[GeO2] glasses, by irradiation with excimer (ArF, KrF or XeCl) laser light, was found to occur via 2-photon absorption processes. Although the wavelength of KrF laser light corresponded to the absorption band of pre-existing O-deficient defects that were associated with Ge ions, no significant difference in the formation efficiency was detected between ArF and KrF laser light. The efficiency for XeCl laser light was smaller, by 4 orders of magnitude, than that for ArF or KrF light. However, it was still larger by an order of magnitude than the formation efficiency of Si E’ centers in SiO2 glasses under ArF laser light. It was shown that the defect-formation efficiencies in the case where the 2-photon energy was close to the optical band-gap were much lower than those when the 2-photon energy was sufficient to exceed the band gap.

H.Hosono, H.Kawazoe, J.Nishii: Physical Review B, 1996, 53[18], R11921-3