Synthesis and characterization of diamonds with different nitrogen concentrations under high pressure and high temperature conditions

In this study, {111}-oriented diamond crystals with different nitrogen concentrations were successfully synthesized in a series of experiments at 5.8 GPa pressure and 1380-1400 degrees C temperature. The nitrogen-vacancy (NV) centers were investigated in diamonds with different nitrogen concentrations. The Raman measurements indicated that the nitrogen atoms caused the Raman peaks to shift to a lower frequency. The photoluminescence (PL) results showed that the intensity of the negatively-charged nitrogen-vacancy (NV-) centers increased with the increase in the nitrogen content when the diamonds had low nitrogen content (<80 ppm). With a further increase in the nitrogen content in the diamond crystals (>372 ppm), the intensity of the NV- centers gradually decreased until it became undetectable. Additionally, we found that the neutral nitrogen-vacancy (NV0) centers were more common in diamonds with low nitrogen content. We believe that the results of this study provide a better understanding of the relationship between the nitrogen content and the NV centers in high pressure and high temperature (HPHT) synthetic diamonds.