Effects of S on the synthesis of type Ib diamond under high pressure and high temperature

In this study, single crystal diamonds were successfully synthesized in a FeNi-S-C system under the constant conditions of 5.5 GPa and 1400 °C. The growth rate of the diamonds decreased due to the existence of sulfur (S) in the synthesis system. The color of the diamonds changed from yellow to light yellow with an increase in the S content. Compared to common type Ib diamonds synthesized in a FeNi-C system, the nitrogen concentration was higher in the synthesized diamonds when 0.1 wt% S was added but was lower when the amount of S was increased to 0.25 wt%. Raman measurements indicated that the use of S had almost no effect on the diamond lattice structure, thus diamond crystals with a high-quality sp3 structure were obtained. The photoluminescence (PL) spectra showed that the nitrogen-vacancy (NV) center occurred more likely in diamond lattice growth along the {111} face. Compared to the NV− center, the NV0 center could not be easily generated in the type Ib diamond lattice without the addition of S. Even if the NV0 and NV− centers were generated simultaneously in the diamond lattice with the addition of 0.25 wt% S, the intensity was higher for the NV− peak than for the NV0 peak. The results of this study improve our understanding of the formation mechanisms of natural diamonds and represent an effective method for controlling the NV center in the diamond lattice.