A study was made of the electron spin resonance characterization of the predominant paramagnetic defects created in pure diamond by neutron irradiation followed by annealing at above 1150C. Together with the previously reported R7, R8, R10a, and R12 centers, two extra S = 1 centers, labelled R7a and KUL13, and two S = 1/2 centers KUL14 and KUL15 were detected. From the angular variation of the electron spin resonance line positions, the symmetry of the R7, R7a, KUL13, KUL14 and KUL15 centers was deduced to be monoclinic-I, C2v, C3v, monoclinic-I and almost C2v, respectively. Analysis of the D matrix properties suggested that the R7, R7a and R8 centers originated from multi-vacancy complexes, where unpaired electrons were separated by 3 vacancy sites. Those centers were tentatively associated with closed structures of 11, 9 and 13 vacancies, respectively.

Vacancy Clusters in Diamond Studied by Electron Spin Resonance. K.Iakoubovskii, A.Stesmans: Physica Status Solidi A, 2004, 201[11], 2509-15