Vacancy clusters in diamond studied by electron spin resonance

We report on the electron spin resonance characterization of dominant paramagnetic defects created in pure diamond by neutron irradiation followed by annealing at temperatures above 1150 °C. Along with the previously reported R7, R8, R10a, and R12 centers, two extra S = 1 centers, labeled as R7a and KUL13, and two S = 1/2 centers KUL14 and KUL15 have been detected and characterized. From the angular variation of the ESR line positions, the symmetry of the R7, R7a, KUL13, KUL14 and KUL15 centers was inferred as monoclinic-I, C2v, C3v, monoclinic-I and almost C2v, respectively. The analysis of the D matrix properties suggests that the R7, R7a, and R8 centers originate from multivacancy complexes, where unpaired electrons are separated by three vacancy sites. Those centers were tentatively associated with closed structures of eleven, nine and thirteen vacancies, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)