High pressure synthetic diamond: optical studies of nickel related defects

The optical spectrum of synthetic diamond, grown by the high pressure method using a nickel-containing alloy as solvent catalyst is quite different not only from the one of natural diamond and that of diamond films, but also from the one of other high pressure diamond synthesised using a catalyst not containing Ni. We report high resolution optical studies of the 1.885 eV system present in the spectrum of synthetic diamonds containing Ni and a high concentration of N (> 50 ppm). Temperature dependence measurements show that this system consists of by 3 zero-phonon lines, which, using uniaxial stress, we show occurance at a rhombic I symmetry defect in transitions between a common ground state A1 into three excited states transforming as the B1 representation of the C2v point group. A model for the defect is suggested.