The electronic structure of V-centers

By X-irradiation of alkali halides (LiF, NaCl, KCl and KBr) at liquid nitrogen temperature electron defect centers are created which can be described as halogen2− molecule-ions oriented along the [110]-axes of the crystal. The electronic structure of this defect has been deduced from the hyperfine interaction studied by means of electron spin resonance. The detailed analysis of the electron spin resonance spectra together with experiments on alkali halides containing Tl+-ions suggests that the halogen2− molecule-ion is not associated with any other imperfection. Thus, the defect might be regarded as a self-trapped hole.