Optically detected electron paramagnetic resonance of Ni-related defects in synthetic diamond crystals

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Abstract
Synthetic diamond crystals grown using a solvent catalyst that contains Ni were studied by optical detection of electron paramagnetic resonance (ODEPR) using the magnetic circular dichroism of the optical absorption (MCDA). The MCDA spectra in the infrared spectral region consist of a derivative-like line at 1.06 eV, single sharp lines at 1.29 and 1.40 eV, a complex phonon-split band with the zero-phonon line (ZPL) at 1.69 eV and a derivative-like doublet structure superimposed at 1.72 eV. All of these optical absorptions were shown to originate from paramagnetic defects. Using ODEPR it was possible to unambiguously assign the 1.72 eV doublet to the NE4 centre and the 1.40 eV line to the NIRIM-2 centre. The defect responsible for the ZPL at 1.06 eV has the same symmetry as the NIRIM-2 centre with a slightly larger -value. The NE4 centre was assigned to substitutional associated with a carbon vacancy in a nearest-neighbour position whereas the NIRIM-2 centre was assigned to interstitial with a distortion along a [111] axis.