title: Photochemical process of divalent germanium responsible for photorefractive index change in GeO2-SiO2 glasses.
abstract: The photoluminescence spectra of the divalent Ge (Ge2+) center in GeO2-SiO2 glasses with different photosensitivities were investigated by means of excitation-emission energy mapping. The ultraviolet light induced photorefractivity has been correlated with the local structure around the Ge2+ centers. The glasses with a larger photorefractivity tended to exhibit a greater band broadening of the singlet-singlet transition on the higher excitation energy side accompanied by an increase in the Stokes shifts. This strongly suggests the existence of highly photosensitive Ge2+ centers with higher excitation energies. It is also found that the introduction of a hydroxyl group or boron species in GeO2-SiO2 glasses under appropriate conditions modifies the local environment of Ge2+ leading to an enhanced photorefractivity.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Sakoh
authors.forename: Masahide
authors.initials: M
authors.lastname: Takahashi
authors.forename: Toshinobu
authors.initials: T
authors.lastname: Yoko
authors.forename: Junji
authors.initials: J
authors.lastname: Nishii
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nishiyama
authors.forename: Isamu
authors.initials: I
authors.lastname: Miyamoto