EPR study of the transformations in nickel containing centres at heated synthetic diamonds

Electron paramagnetic resonance (EPR) was used to investigate the transformation of as grown nickel and nitrogen defects at the annealing of synthetic diamonds, obtained by the temperature gradient method. Structural models and formation mechanisms of the seven nickel containing paramagnetic centres (NE1-NE7) in synthetic diamonds are discussed. A common structural fragment of NE1-NE4 centres is a double semivacancy, in centre of which Ni+ ion is located. The NE6, NE7 centres are proved to operate as shallow electronic traps. The effects observable for NE5 centres are supposed due to an internal electronic transformation in them. The problem of charge compensators for nickel ions is also discussed. The features observable in the charge transfer processes under X-ray irradiation for nickel and nitrogen containing centres suggest that donor nitrogen serves as a bulk charge compensator for substitutional nickel and NE1 centres.