Multi-frequency ESR analysis of the E′

A multifrequency electron spin resonance study of the E′δ defect in six SiO2 glasses irradiated by UV, VUV, or 60Co γ-rays, points to an electronically rigid structure with no dynamic rearrangement occurring in the temperature range T ≥ 4.2 K. Reassuringly coinciding over all frequencies and T's applied, the average intensity ratio of the 100 G 29Si hyperfine doublet to the central Zeeman signal points to delocalization of the unpaired spin over n = 4 or 5 equivalent Si sites, thus refuting the Si dimer model. A noteworthy revelation is that E′δ is only observed in those (3) silica types studied also showing the Al E′ center in the as γ-irradiated state. This may signify some indirect role of charge compensators/traps in activating/stabilizing E′δ centers, relevant to further theoretical modeling