PARAMAGNETIC RESONANCE OF ROOM-TEMPERATURE-STABLE V-TYPE CENTERS IN GAMMA-IRRADIDATED ALKALI HALIDE-BORON OXIDE GLASSES

Numerous glasses were prepared from mixtures of alkali halides and boron oxide and subjected to 60Co γ rays at room temperature; these were examined by ESR techniques at 9.1 and 35 GHz. The induced spectra can be divided into two categories: (1) a resonance due to boron-oxygen centers previously studied in alkali borate glasses, and (2) certain new resonances which are shown to be due to F-type centers (halogen2- molecule ions). The Cl2- species is stable at room temperature; its spin-Hamiltonian parameters determined by means of a computer simulation of the spectrum are: g∥ = 2.0042, g⊥ ≈2.035, 35-35A∥ = 100 G, 35-35A⊥≈8 G. Inclusion of small amounts of KCl or LiCl in borate glasses can result in nearly total suppression of the usual boron-oxygen-center resonance, i.e., the dissolved chloride ions prove to be the more efficient hole traps. The Br2 - centers can also be formed, but less efficiently. The F-T centers are not produced in borate glasses which is consistent with other data which suggest that fluorine forms covalent bonds with boron in these materials.