Trigonal S = 1 NOL1/NIRIM5 center was characterized by electron spin resonance in Ni- and B-doped diamond grown by the high-pressure high-temperature technique. Hyperfine interaction structure was detected and attributed to six equivalent C sites and one Ni site. Analysis of the electron spin resonance parameters strongly suggested assignment of the NOL1/NIRIM5 center to interstitial Ni2+ ion (3d8 configuration) situated in the center of a diamond divacancy.

Ni-Vacancy Defect in Diamond Detected by Electron Spin Resonance. K.Iakoubovskii: Physical Review B, 2004, 70[20], 205211 (5pp)