Paramagnetic Resonance of Room-Temperature-Stable V-Type Centers in γ-Irradidated Alkali Halide–Boron Oxide Glasses

Numerous glasses were prepared from mixtures of alkali halides and boron oxide and subjected to ⁶⁰Co $\gamma$ 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 V‐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: $\text{g‖\hspace{0.17em}=\hspace{0.17em}2.0042}$ , $\text{g⊥\hspace{0.17em}≃\hspace{0.17em}2.035}$ , ${}^{\text{35–35}}\text{A‖\hspace{0.17em}=\hspace{0.17em}100 G}$ , ${}^{\text{35‐35}}\text{A⊥≃8 G}$ . 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 F₂⁻ 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.