No abstract

Photochemical reactions related to the Ge lone-pair center ͑GLPC͒ that are induced by KrF excimer laser photons in H 2 -loaded Ge-doped SiO 2 glass have been investigated. Without the H 2 loading, the Ge electron center ͑GEC͒ and the positively charged GLPC were induced by the laser irradiation. In the H 2 -loaded sample, the GEC, the Ge EЈ center, and the germyl radical ͑GR͒ were induced by the irradiation, while the positively charged GLPC was not observed after the irradiation. If the H 2 -loaded sample was thermally annealed after the photon irradiation, the concentration of the photo-induced GEC decreased monotonically with an increase in the annealing temperature. On the other hand, the concentration of the GR increased up to the annealing temperature of 160°C, and it decreased at higher temperatures. Without the pre-irradiation, the induction of the GR was not observed even in the H 2 -loaded sample. From these results, it is concluded that the positively charged GLPC is terminated with a hydrogen atom in the H 2 -loaded sample and then becomes the GR by trapping an electron thermally released from the GEC. ͓S0163-1829͑99͒05631-3͔ PHYSICAL REVIEW B 15 AUGUST 1999-I VOLUME 60, NUMBER 7 PRB 60 0163-1829/99/60͑7͒/4682͑6͒/$15.00 4682

Changes in concentrations of the photo-induced paramagnetic centres, Ge centre, Ge electron centre (GEC) and positively charged Ge lone-pair centre in four Ge-doped glasses with Ge contents of 1.0, 1.4, 6.9 and 9.2 mol% were investigated, using a KrCl excimer lamp (5.6 eV, 7.0 mW ) and a KrF excimer laser (5.0 eV, 4 MW ) as photon sources. When the glasses were irradiated with photons from the lamp, the Ge centre and the GEC were induced in all the glasses. However, the was observed only in the sample with Ge content of 1.4 mol% where the concentration of the induced Ge centre was smaller than that of the induced GEC. The irradiation of photons from the laser induced the GEC and in all the glasses. When the photon irradiation from the laser was continued onto the glasses, the Ge centres were induced and the concentration of the wasf found to decrease with an increase in the concentration of the Ge centres. From these phenomena, it was concluded that the generation of the Ge centres diminishes the concentration of the .