Photochemical reaction of divalent-germanium center in germanosilicate glasses under intense near-ultraviolet laser excitation: Origin of 5.7 eV band and site selective excitation of divalent-germanium center

The photochemical reaction of Ge ²⁺ in 10GeO ₂- 90SiO ₂ optical fiber preform and the origin of the 5.7 eV optical absorption band induced by intense ultraviolet laser excitation have been investigated using a near-ultraviolet XeF excimer laser (3.7 eV) as the main excitation source. Based on the previous and present experimental results, it is concluded that the 5.7 eV optical absorption band does not originate from the Ge(2) electron trapped center. In place of this model, we have proposed an alternative structural model for the origin of the 5.7 eV band taking into account the experimental fact that the corresponding center is diamagnetic. In addition, it is found that the site selective excitation of the Ge ²⁺ center can be achieved by using laser sources with different photon energies.