A study was made of the trapped hole center, and the hyperfine structure of the electron spin resonance spectrum indicated that the unpaired electron spin interacted mainly with a 11B nucleus. The parameters of the electron spin resonance spectra were deduced to be gxx = 2.032, gyy = 2.020 and gzz = 2.007. It was concluded that the electron spin resonance spectrum was consistent with a model for the center which involved a hole that was trapped at an O ion which bridged two B atoms (one of which was 3-coordinated while the other was 4-coordinated) in the vicinity of the negatively charged stabilizing structural defects. It was suggested that the most likely candidate for this stabilizing defect was a Li vacancy which was created either during growth, or by ionizing radiation.

I.N.Ogorodnikov, A.V.Porotnikov, S.V.Kudyakov, A.V.Kruzhalov: Materials Science Forum, 1997, 239-241, 337-40