A large number (>60) of N-containing type-Ia natural diamonds, and N-free type-IIa natural and synthetic diamonds, were electron-irradiated and their optical absorption spectra were analyzed in detail. The analysis revealed that the concentrations of vacancies [V] and interstitials [I0 ] in type-IaA diamonds increase linearly with the concentration [NA ] of the A-form of N. This increase of [V] and [I0] with [NA ] was attributed to the trapping of vacancies and interstitials in the strain field of N. The trapping produces so-called strained vacancies and partly immobilizes interstitials, thus reducing the vacancy–interstitial recombination during electron irradiation, thereby increasing [V] and [I0 ]. Those strained vacancies and interstitials recombine upon annealing at 390 to 420C. In type-IaB diamonds no correlation was found between [V] and the concentration [NB ] of the B-form of N. Moreover, [I0] was found to decrease linearly with [NB ]. In both type-IaA and type-IaB diamonds, the width of the GR1 zero-phonon line, associated with the neutral vacancies [V0 ], increased with N concentration. A new, more appropriate and accurate formula to calculate [V0] was proposed; based upon measuring the height of the GR1 absorption band at 2.0eV.

Electron Irradiation and the Formation of Vacancy–Interstitial Pairs in Diamond. I.Kiflawi, A.T.Collins, K.Iakoubovskii, D.Fisher: Journal of Physics - Condensed Matter, 2007, 19[4], 046216 (15pp)