C hyperfine interactions in the ground state of the negatively charged nitrogen vacancy ͑NV − ͒ center have been investigated using electron-paramagnetic-resonance spectroscopy. The previously published parameters for the 14 N hyperfine interaction do not produce a satisfactory fit to the experimental NV − electron-paramagnetic-resonance data. The small anisotropic component of the NV − hyperfine interaction can be explained from dipolar interaction between the nitrogen nucleus and the unpaired-electron probability density localized on the three carbon atoms neighboring the vacancy. Optical spin polarization of the NV − ground state was used to enhance the electron-paramagnetic-resonance sensitivity enabling detailed study of the hyperfine interaction with 13 C neighbors. The data confirmed the identification of three equivalent carbon nearest neighbors but indicated the next largest 13 C interaction is with six, rather than as previously assumed three, equivalent neighboring carbon atoms.

Studies carried out at the DTC Research Centre have shown that single-crystal CVD synthetic diamond is clearly distinguishable from natural diamond. This article presents information about the CVD process, the history of its development, the different kinds of CVD synthetic diamond material that can be produced, and properties that differentiate them from natural diamond. The authors studied more than a thousand CVD synthetic diamond samples that were grown for research purposes using a range of different process conditions. Absorption, photoluminescence, and cathodoluminescence spectra of these CVD synthetic diamond samples showed a range of different impurity-related features not seen in natural diamond. Photoluminescence imaging is also useful in identifying CVD synthetic diamond, and X-ray topography may give supportive evidence. The effectiveness of the Diamond Trading Company Diamond Verification Instruments for identifying CVD synthetic diamond is also described.

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The zero-phonon line (ZPL) at 1.68 eV has been attributed to the negatively charged silicon split-vacancy center in diamond, (Si-V) − , and has been extensively characterized in the literature. Computational studies have predicted the existence of the neutral charge state of the center, (Si-V) 0 , and it has been experimentally observed using electron paramagnetic resonance (EPR). However, the optical spectrum associated with (Si-V) 0 has not yet been conclusively identified. In this paper the 1.31 eV band visible in luminescence and absorption is attributed to (Si-V) 0 using an approach which combines optical absorption and EPR measurements. The intensities of both 1.68 eV and 1.31 eV bands are found to increase in deliberately Si-doped chemical vapor deposition (CVD) grown diamond, and also after electron irradiation and annealing, suggesting the involvement of both Si and a vacancy in the centers. The 1.31 eV ZPL is unambiguously associated to Si by its shift to a lower energy when the dominant Si isotope is changed from 28 Si to 29 Si. Charge transfer between (Si-V) − and (Si-V) 0 induced via ultraviolet photoexcitation or heating in the dark allows calibration factors relating the integrated absorption coefficient of their respective ZPLs to the defect concentration to be determined. Preferential orientation of (Si-V) 0 centers in CVD diamond grown on {110}-oriented diamond substrates is observed by EPR. The (Si-V) 0 centers are shown to grow predominantly into CVD diamond as complete units, rather than by the migration of mobile vacancies to substitutional Si (Si S ) atoms. Corrections for the preferential alignment of trigonal centers for quantitative analysis of optical spectra are proposed and the effect is used to reveal that the 1.31 eV ZPL arises from a transition between the 3 A 2g ground state and 3 A 1u excited state of (Si-V) 0 . A simple rate equation model explains the production of (Si-V) 0 upon irradiation and annealing of Si-doped CVD diamond. In as-grown Si-doped diamond the (Si-V) defects only account for a fraction of the total silicon present; the majority being incorporated as Si S . The data show that both Si S and (Si-V) are effective traps for mobile vacancies.

We report the identification of the nitrogen-vacancy-hydrogen complex in a freestanding nitrogen-doped isotopically engineered single crystal diamond synthesized by chemical vapor deposition. The hydrogen atom is located in the vacancy of a nearest-neighbor nitrogen-vacancy defect and appears to be bonded to the nitrogen atom maintaining the trigonal symmetry of the center. The defect is observed by electron paramagnetic resonance in the negative charge state in samples containing a suitable electron donor (e.g., substitutional nitrogen N(0)(S)).