Effects of high pressure and high temperature annealing on the characteristics of HPHT diamonds with high nitrogen content

Abstract

The influence of nitrogen impurities on diamond is an issue that deserves continuous attention, and annealing is an important method to change the state of nitrogen in diamond. In this paper, C3H6N6 doped diamonds with high nitrogen content were synthesized then annealed at high pressure and high temperature (HPHT). After HPHT annealing, the transparency of high nitrogen diamond improved, and the pyramidal defects on the surface of nitrogen-containing diamond disappear or are destroyed. The infrared spectra show annealing causes a change in the state of aggregation of some of the nitrogen in high-nitrogen diamonds from C center to A center. Raman spectra show that the higher the nitrogen content is, the more the characteristic peaks shift is and the wider the FWHM (full width at half maxima) of diamond is. Annealing has a little effect on the position and FWHM of Raman peaks. PL spectra show that proper nitrogen concentration is conducive to increase the concentration of NV− in diamond. In addition, we found that un-doped diamond crystals synthesized by the high temperature and high pressure method had a high NV− colour center concentration after annealing. The results are helpful to further understand the defects related to nitrogen impurities in diamond.