Formation mechanism of defect centers in GeO 2-doped silica glass

Abstract

This paper describes the formation mechanism of defect centers in GeO2-doped silica glass. Both Si and Ge E′ centers are induced by fiber drawing in silica optical fibers with GeO2 contents below 0.4 mol%. However, Ge E′ centers alone are observed above the critical GeO2 content. On the other hand, in glass irradiated with γ-ray at room temperature, both Ge-associated centers (GACs) and Si E′ centers are observed in 0.4 mol% GeO2 content. However, GACs alone are observed in higher content. Furthermore, annealing causes not only a decrease in GACs but also an increase in Si E′ centers in irradiated silica glass with 0.4 mol% GeO2 content. The transformation from GACs to Si E′ centers is considered to result from the electron migration. The electron mean free path is estimated at about 1.4 ran from the nearest-neighbor interatomic distance between Ge atoms.