Changes in concentrations of the photo-induced paramagnetic centres, Ge E′ centre, Ge electron centre (GEC) and positively charged Ge lone-pair centre ((GLPC) +) in four Ge-doped SiO 2 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 cm -2) and a KrF excimer laser (5.0 eV, 4 MW cm -2) as photon sources. When the glasses were irradiated with photons from the lamp, the Ge E′ centre and the GEC were induced in all the glasses. However, the (GLPC) + was observed only in the sample with Ge content of 1.4 mol% where the concentration of the induced Ge E′ centre was smaller than that of the induced GEC. The irradiation of photons from the laser induced the GEC and (GLPC) + in all the glasses. When the photon irradiation from the laser was continued onto the glasses, the Ge E′ centres were induced and the concentration of the (GLPC) + was found to decrease with an increase in the concentration of the Ge E′ centres. From these phenomena, it was concluded that the generation of the Ge E′ centres diminishes the concentration of the (GLPC) +.
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