Possible models were proposed for a new electron paramagnetic resonance center (NOL1) which was observed in a diamond grown from a Ni-containing solvent catalyst with a Ti getter for N. It was found that Ni and B were the most prevalent impurities. The center had trigonal (C3v) symmetry about <111>, with S = 1, g|| = 2.0235, g = 2.0020 and D = -171GHz. The electron paramagnetic resonance lineshape was unusual, and this was tentatively attributed to a partially resolved 11B hyperfine structure. This center was suggested to be the same as NIRIM-5, which was observed in B-doped synthetic diamond. The most likely structure for this center was expected to be an interstitial Ni2+ with a substitutional B- ion at the nearest-neighbour site along <111>.

EPR Studies of a Nickel–Boron Centre in Synthetic Diamond. V.A.Nadolinny, J.M.Bak

M.E.Newton, H.Kanda: Diamond and Related Materials, 2002, 11[3-6], 627-30