It was recalled that the E’ center was an archetypal radiation-induced defect whose peculiar electron paramagnetic resonance and hyperfine activity had been known for over 4 decades. The center had been traditionally identified with a distorted and positively charged O vacancy, V0+. However, no direct proof of the stability of the defect had been provided, and its identity was still unclear. It was proved directly here that the distorted V0+ was metastable and satisfied the key requirements for its identification as being E’: such as the thermal and optical responses, and activation-deactivation mechanisms.

Proof of the Thermodynamic Stability of the E’ Center in SiO2. C.M.Carbonaro, V.Fiorentini, F.Bernardini: Physical Review Letters, 2001, 86[14], 3064-7