Luminescence of fluorine doped silica glass

The role of fluorine doping on silica properties was studied by luminescence methods. Non-doped samples of the same preparation technology possess an absorption band at 7.6 eV on the level of 2 cm−1. A trace of this band in the fluorine-doped sample is on the level of 0.1 cm−1. In both samples 7.6 eV photons as well as ionizing irradiation (X-ray, electron beam) excite photoluminescence of so-called oxygen deficient centers with a blue (2.7 eV) and a UV band (4.4 eV). The luminescence of the fluorine doped sample increases with dose many times from the initial low level for the same excitation. Also, thermally stimulated luminescence appears after irradiation. The energetic yield under ionizing irradiation of induced luminescence is the same level as reference samples. The decay kinetics of cathodoluminescence show that the blue band decays faster and the UV band decays more slowly than was known for the oxygen deficient center. It is concluded that structural imperfections, responsible for the absorption band at 7.6 eV, remain similar in silica glasses during preparation; however fluorine changes the electronic transition nature and, therefore, the absorption band is of low intensity. Such imperfections, passivated with fluorine, interact with electronic excitation produced by radiation. Transient changes of imperfections geometric and electronic configurations take place with probable removal of fluorine, and that provides a growth of the luminescence centers even at low temperature and changes the decay relatively to intra-center luminescence. Therefore the fluorine-doped sample is similar to the non-doped samples through corresponding recombination luminescence of oxygen deficient centers.