Photochemical reaction of hydrogen with germanosilicate glass initiated by 34–54-eV ultraviolet light

By measuring the photosensitivity of Ge-doped silica fibers over the 3.4–5.4-eV spectral range and from $T=95 \mathrm{K}$ to $T=375 \mathrm{K}$, we demonstrate that different physical mechanisms take place depending on whether ${\mathrm{H}}_2$ is present. Without ${\mathrm{H}}_2$ the principal photosensitivity pathway involves excitation of a germanium oxygen-deficient center to its triplet state. In ${\mathrm{H}}_2$-loaded fibers the UV light excites the regular Ge—O bond, which then reacts with ${\mathrm{H}}_2$ to produce Si—OH or Ge—OH and a ${\mathrm{GeE}}^{\prime }$ center.