Optical absorption measurements were performed on irradiated diamonds which contained various concentrations of N defects. Analysis of the results suggested that single substitutional N centres trapped vacancies some 8 times more efficiently than did substitutional N pairs. An unknown infra-red spectrum was observed for irradiated crystals with a low impurity content, and for synthetic diamond films, and was attributed to intrinsic defects.

Trapping of Vacancies by Defects In Diamond. K.Iakoubovskii, G.J.Adriaenssens: Journal of Physics - Condensed Matter, 2001, 13[26], 6015-8