Optical absorption measurements of various growth sectors of a polished slice of electron-irradiated type-Ib synthetic diamond showed that the vacancy concentration was almost 4 times higher in the high-N {111} sectors than in the low-N {115} sectors. Evidence showed that the self-interstitials were trapped by N, thus reducing the amount of correlated recombination with vacancies which occurred in the absence of N.

The Production of Vacancies in Type-Ib Diamond. A.T.Collins, A.Dahwich: Journal of Physics - Condensed Matter, 2003, 15[37], L591-6