The effect of nitrogen impurity on the annealing of radiation damage in diamond

Impurity nitrogen in type Ia diamond is known to trap radiation damage centres during annealing. Most of the nitrogen is also known to be present in two forms, labelled A and B from the absorption peaks produced by them in the range 1000-1332 cm-1. In this paper, the effect of these different forms of nitrogen on the annealing of radiation damage is considered. The visible absorption spectra of 41 annealed diamonds have been compared with their infrared spectra. The results suggest that the A form of nitrogen produces the 2.463 eV centre, while the B form gives the 2.499 eV centre, by trapping a radiation damage centre during annealing. The trapping centres compete with each other for the damage centres. In natural type Ib diamond (containing paramagnetic nitrogen), the 640nm (1.945 eV) centre is produced by the annealing, in agreement with du Preez (1965).