Acceptor level of substitutional Ni in diamond

Substitutional ${\mathrm{Ni}}^{\mathrm{-}}$ in synthetic diamonds has been investigated by electron-paramagnetic resonance (EPR) and photo-EPR. The photo-EPR investigation shows that the ${\mathrm{Ni}}^{\mathrm{-}}$ EPR signal can be diminished by optical illumination, and the threshold energy of 2.47±0.02 eV suggests that the acceptor level is located at 3.03 eV above the valence band. The energy dependence of the optical cross section for the electron ionization ${\mathrm{\sigma }}_{\mathit{n}}$ was determined from an analysis of the EPR transients.