A 15.7mol%GeO2 glass was prepared by using a vapor axial deposition method, and optical absorption at 4.92 and 5.08eV was observed between 300 and 600K. The results were then compared with electron spin resonance data for the same samples. The absorption at 4.92eV was found to increase with increasing temperature, while the optical absorption at 5.08eV decreased with increasing temperature. These changes in optical absorption indicated that the concentration of the neutral O mono-vacancy was reduced at higher temperatures. The changes were reversible. The concentration of the Ge E' center, as estimated from electron spin resonance data, increased with increasing temperature; in contrast to a decrease in the neutral O mono-vacancy. The results strongly suggested the existence of thermal equilibrium reactions between neutral O mono-vacancies and Ge E' centers.

M.Takahashi, T.Fujiwara, T.Kawachi, A.J.Ikushima: Applied Physics Letters, 1998, 72[11], 1287-9