An orthorhombic nickel-nitrogen complex in high-pressure synthetic diamond

We report uniaxial stress measurements on the 1.693 eV zero-phonon line, observed on nickel- and nitrogen-containing synthetic diamonds after annealing at 1600 degrees C. We show that the line is an electric dipole transition which occurs at a defect of rhombic I symmetry. The shape of the vibronic sideband and the temperature dependence of the zero-phonon intensity may be understood assuming linear coupling to totally symmetric vibrational modes. Quadratic coupling to a single quasi-localised non-symmetric mode is invoked to explain a temperature-induced transition 7 meV below the zero-phonon line energy. (C) 1999 Elsevier Science B.V. All rights reserved.