Ultraviolet-radiation-induced chemical reactions through one-and two-photon absorption processes in GeO_2–SiO_2 glasses

Abstract

Photochemical reactions in 10 GeO₂ –90 SiO₂ glass induced by irradiation with excimer lasers (KrF, 5.0 eV, XeCl, 4.0 eV) and a Hg lamp (4.9 eV) were examined. The irradiation with excimer lasers generated two types of paramagnetic defect, an electron-trapped center associated with fourfold coordinated Ge ions and a self-trapped hole center on bridging oxygen. Taking the optical band gap (~7.1 eV) of the glass obtained in this work and the power density of laser pulses [10–90 mJ/(cm² pulse), pulse duration 20 ns] into account, we concluded that these centers were formed by band-to-band excitation by two-photon absorption process. On the other hand, the lamp illumination (~16 mW/cm²) caused the formation of Ge E′ centers from preexisting oxygen-vacancy-type defects by the one-photon absorption process. These two kinds of reaction proceed independently, depending on the power densities of UV beams, at least in our experimental condition.