Formation processes of paramagnetic centers in ${\mathrm{GeO}}_{2}{\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ glasses by irradiation with KrF excimer-laser pulses (5 eV) were investigated at 77 K using electron-spin resonance (ESR). The essential photochemical reaction was the pair generation of electron-trapped centers associated with fourfold coordinated Ge ion (GEC) and self-trapped hole centers of bridging oxygen (STH). This reaction proceeds by band-to-band excitation via two-photon absorption process. A part of GEC was converted to $\mathrm{Ge}{E}^{\ensuremath{'}}$ center during prolonged irradiation at 77 K. The difference between ESR spectra before and after annealing at room temperature revealed that the majority of STH disappears by recombination with GEC (or $\mathrm{Ge}{E}^{\ensuremath{'}})$ during annealing at room temperature. The dominant paramagnetic centers remaining after annealing were GEC and $\mathrm{Ge}{E}^{\ensuremath{'}},$ and their total concentration was approximately 50% of those before annealing. The intimate relation between the generation of paramagnetic centers and the decay of emission due to ${\mathrm{Ge}}^{2+}$ suggested that the hole transfer from STH to ${\mathrm{Ge}}^{2+}$ is followed by their structural relaxation.