Simultaneous generation of the 7.6-eV optical absorption band and F2 molecule in fluorine doped silica glass under annealing

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Abstract
We examined chemical state of fluorine doped silica glasses and its thermal behavior. Almost all of the fluorine atoms were found to have the ≡SiF structure with Raman spectroscopy. No optical absorption in the region of 3–9 eV was detected in the glass. When the glasses were annealed in a He atmosphere at 1000 °C, absorption bands peaking at 7.6 and 4.3 eV appeared. These two bands are attributed to the ≡SiSi≡ structure and to F2 molecules, respectively. We proposed a thermal decomposition reaction expressed as ≡SiF+FSi≡→≡SiSi≡+F2. The concentrations of the reaction products, ≡SiSi≡ and F2, estimated from the absorption cross sections were equal to each other within the errors of measurements. We also examined the radiation damage with γ ray. The concentration of E’ center was almost the same for the same dose in silica glasses having different concentrations of FSi≡ and ≡SiSi≡. We suggest that FSi≡ and ≡SiSi≡ were found to be stable for γ‐irradiation at room temperature.