Adjustable charge states of nitrogen-vacancy centers in low-nitrogen diamond after electron irradiation and subsequent annealing

In this work, we investigate the photoluminescence spectra of nitrogen-vacancy (NV) centers in low-nitrogen diamond under 200 keV electron irradiation. We discuss the dependence of NV center charge states on annealing temperature, laser excitation power, and measurement temperature. The results show that the NV centers in low-nitrogen diamond are more likely to exist in the form of NV0 centers. Annealing breaks the charge balance between two charged NV centers, and, as the annealing temperature increases (300–800 °C), NV− centers are converted into NV0 centers. Meanwhile, the NV intensities significantly increase when the nitrogen atoms capture the vacancies after electron irradiation and subsequent annealing. With increases in laser power, the NV− centers are more prone to Auger recombination, and thus, the NV− centers are converted into NV0 centers. In addition, the NV centers are quenched by increases in measurement temperature, but the measurement temperature does not affect their intensity ratio. This result indicates that low-nitrogen diamond becomes more likely to form stable NV0 and NV− centers at different measurement temperatures.