Radiation-induced defect centers in high-purity GeO2 glass

Abstract

Defect centers induced in GeO2 glass by either 100-KeV x rays at 77 K or γ rays at room temperature were studied by electron-spin resonance. The model of a singly charged oxygen vacancy defect center for the Ge E′ center (g∥ =2.0012, g⊥ =1.9945) was confirmed by the observation and computer simulation of the 73Ge hyperfine structure associated with this center. The evolutions of the Ge E′, peroxy radical, and nonbridging oxygen hole centers were studied by isochronal thermal annealing. Surprisingly, the Ge(2) center, a defect previously known only in Ge-doped silica, and an additional center with a hyperfine coupling constant half that of the Ge E′ center were found in pure GeO2 samples irradiated at 77 K; these, too, were studied by isochronal thermal annealing and computer simulation. Structural models for these centers are presented.