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

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Abstract
Electron paramagnetic resonance (EPR) and photo-EPR investigations on synthetic diamond crystals have allowed an unambiguous determination of nickel-related defect levels in the diamond bandgap. Indirect photoinduced recharging of the nitrogen donor and detection of two complementary photoionization transitions involving the substitutional nickel show that the Ni-/0s acceptor state is located at 2.49±0.03 eV below the conduction band. A strong decrease of the AB5 EPR signal intensity is induced by irradiation of the samples with photon energies hν>1.88 eV. Observation of a recharging process upon photoexcitation with hν>2.5 eV yields the localization of the AB5 defect level position at E = EC-1.88±0.03 eV.