Analysis of Complex ESR Spectra Induced in Potassium Borate Glasses

Electron spin resonance studies showed that gamma-irradiated potassium borate glasses display complex spectra. These were resolved into five overlapping resonances by a thermal bleaching technique. The resonances differ in nature and stability, suggesting that they belong to different paramagnetic centers (I, II, III, IV, and V) induced by irradiation. The relative concentrations of these centers change with K₂O concentration; the stability increases in the order V1⋍2.002, g₂⋍2.010, g₃⋍2.034; (II) g_avg⋍2.0087; (III) g⋍2.008; (IV) g⋍2.002; and (V) g⋍2.000. These values suggest that centers I, II, and III may be caused by trapped-hole centers, whereas centers IV and V are attributed to trapped electron centers. Centers I and II have hyperfine structures with an ¹¹B nucleus producing a five-line-plus-a-shoulder spectrum and a four-line spectrum, respectively. The resonance attributed to center V was very weak and was observed only in glasses which contained more than 20 mol% K₂O.