On the existence of positively charged single-substitutional nitrogen in diamond

Infra-red (IR) absorption results on irradiated and annealed synthetic diamond are presented which confirm an earlier proposal that a component found in the defect-induced one-phonon region of some diamonds arises from positively charged single-substitutional nitrogen (N+). The concentration ratio of N+ to neutral substitutional nitrogen (N-0) centres may be changed by shining light of various energies onto the examined samples. By correlating changes in absorption of the IR component associated with N-0 centres with changes in the N+ component, and using a previously determined relation between the concentration of N-0 centres and peak absorption coefficient at 1130 cm(-1), the relationship between peak absorption at 1332 cm(-1) and concentration of N+ centres has been derived, namely 1 cm(-1) of absorption is produced by (5.5 +/- 1) ppm N+ centres. Other defects may also give rise to absorption at 1332 cm(-1), but the N+ component is uniquely identified by further peaks at 1046 and 950 cm(-1). The significance of this component is demonstrated by the bet that some samples can contain in excess of 80 ppm N+ centres, and this must consequently be accounted for when assaying the total nitrogen concentration in such samples. Using the above relationship useful parameters relating the concentration of neutral vacancies, negative vacancies and negatively charged nitrogen-vacancy centres to their respective zero-phonon line integrated absorptions have been derived.