Preparation of IaA-type diamond crystals containing a high concentration of nitrogen by annealing {111}-oriented N-doped diamond crystals

• Gem-quality diamond with N up to 2624 ppm was successfully synthesized by TGM.
• The highest N-aggregation rate was found in high-level N-doped diamond crystal.
• Colorless IaA-type diamond crystal was produced by annealing method.

In this study, we report the growth of gem-quality N-doped {111}-oriented diamond crystals by adding phosphorus nitride (P3N5) into the growth cell at 6.0 GPa pressure and 1550–1650 K temperature. The concentration of nitrogen (CN) incorporated into the synthetic diamond crystals was found to be in the range of 476–2624 ppm, whereas the P impurity could only be detected in the graphite phase. The annealing treatment of the diamond crystals show that the aggregation rate of N atoms in the high-level N-doped diamond crystals is ~ 71 times of that in the conventional synthetic Ib-type diamonds. Therefore, the green color Ib-type diamond crystals containing a higher CN were found to be good candidates for the preparation of IaA-type diamond crystals.

Fig. 1. Optical images of diamond crystal with nitrogen concentration of 1300–1400 ppm before and after annealing treatment.Figure optionsDownload as PowerPoint slide