ULTRAVIOLET-RADIATION-INDUCED CHEMICAL-REACTIONS THROUGH ONE-PHOTON AND 2-PHOTON ABSORPTION PROCESSES IN GEO2-SIO2 GLASSES

Photochemical reactions in 10 GeO2-90 SiO2 glass induced by irradiatio n with excimer lasers (KrF, 5.0 eV, XeCl, 4.0 eV) and a Hg lamp (4.9 e V) were examined. The irradiation with excimer lasers generated two ty pes of paramagnetic defect, an electron-trapped center associated with fourfold coordinated Ge ions and a self-trapped hole center on bridgi ng oxygen. Taking the optical band gap (similar to 7.1 eV) of the glas s obtained in this work and the power density of laser pulses [10-90 m J/(cm(2) pulse), pulse duration 20 ns] into account, we concluded that these centers were formed by band-to-band excitation by two-photon ab sorption process. On the ether hand, the lamp illumination (similar to 16 mW/cm(2)) caused the formation of Ge E' centers from preexisting o xygen-vacancy-type defects by the one-photon absorption process. These two kinds of reaction proceed independently, depending on the power d ensities of UV beams, at least in our experimental condition.