Nitrogen isotope effects in synthetic diamonds

Abstract

The effects of isotopic substitution of the dispersed nitrogen atoms in synthetic diamonds, on several defect centres resulting from radiation damage and annealing, are described. Measurements have been carried out with standard 14N-containing diamonds and diamonds doped with 15N. New features have been found in the infrared region in the wavenumber range 2000-1332 cm-1 as a result of employing heavy neutron doses. In particular, an absorption peak at 1706 cm-1 in standard diamonds is shown to be due to a centre involving one nitrogen atom. In the visible spectral region, changing the nitrogen isotope results in shifts of the energy spacing between the phonon replicas and the zero-phonon line in the 1.945 eV absorption band and the 2.156 eV luminescence band. This suggests that the 2.156 eV centre, as well as the 1.945 eV centre, involves substitutional nitrogen.