Charge transfer excitons in Ge-doped silica fibres and their response to static electric field

Absorption in the region of green light and the corresponding broad band luminescence in Ge-doped silica fibres are measured and interpreted. The spectra obtained show that new type of excitations arises in Ge-doped silica fibres which is absent in pure silica. They are charge transfer excitons. The concentration dependence reveals charge transfers from Ge centers to their hosts as well as transfers between different Ge centers. The orientation ordering of the exciton dipole moments results in positive feedback in response to static electric Grid. This produces the strong phase-matched electric field allowing the effective second harmonic generation. (C) 2000 Published by Elsevier Science B.V. All rights reserved.