ESR spectra and magnetic constants of alpha-Al2O3 : Co2+,H+ and alpha-Al2O3 : Co2+,X+

New anisotropic ESR spectra of Co2+ doped sapphire, different from hitherto known, are reported. The new spectra which are observed, besides the well-known spectra of alpha-Al2O3:Co2+, are shown to form two sets, each one consisting of six spectra (1-6) and (7-12). The spectra of both sets are proven to be interrelated by D-36 symmetry. g and A tensors for each set will be given. Evidence is given that the two sets are to be assigned to the defects alpha-Al2O3:Co2+,H+ and alpha-Al2O3:Co2+,X+. The former is concluded to consist of a Co2+ ion at the substitutional site (c) and a proton located in a potential minimum along a straight line between O2- ions situated in O2- triangles above and below the Co2+ ion. The potential function for the proton has been calculated by quantum-chemical calculations to elucidate the geometrical structure of the paramagnetic center. The defect alpha-Al2O3:Co2+,X+ could not be fully analyzed but some evidence is presented, that X+ might be alkali ions.