Determination of the W8 and AB5 defect levels in the diamond gap

Electron paramagnetic resonance (EPR) and photo-EPR investigations on synth etic diamond crystals have allowed an unambiguous determination of nickel-r elated defect levels in the diamond bandgap. Indirect photoinduced rechargi ng of the nitrogen donor and detection of two complementary photoionization transitions involving the substitutional nickel show that the Ni-s(-/10) a cceptor state is located at 2.49 +/-0.03 eV below the conduction band. A st rong decrease of the AB5 EPR signal intensity is induced by irradiation of the samples with photon energies hv > 1.88 eV. Observation of a recharging process upon photoexcitation with hv > 2.5 eV yields the localization of th e AB5 defect level position at E = E-C - 1.88 +/-0.03 eV.