ESR studies on arsenic-associated centers in oxide glasses produced by gamma-irradiation

Two kinds of new As-associated centers in γ-irradiated 16Na2O.11CaO.73SiO2:0.1AsOsub(x) glass were identified by ESR experiments. The nearly isotropic hyperfine quartet produced by a 75As nucleus (I=3/2, N.A.=100%) appearing in oxidized glass (O-signal) was assigned to an electron-trap center originating from a precursor As5+ ion. The hf quartet of axial symmetry observed in reduced glass was attributed to a hole-trap center originating from an As3+ ion. ESR parameters were evaluated by use of line shape simulation technique. LCAO coefficients were derived from the parameters. The structure models for the centers were proposed on the basis of the coefficients: the electron-trap center, (As5+)-, has a tetrahedral coordination, the trapped electron locating on an As-O anti-bonding MO; the hole-trap center, (As3+)+, has a trigonally pyramidal coordination, the hole occupying a non-bonding As sp3 hybridized orbital