An innovation in obtaining the aggregation N of the synthesized diamond under HPHT conditions

Abstract Diamond crystals were synthesized with CH4N2S additive in FeNiCo–C system at pressure of 6.0 GPa and temperature ranging from 1285 to 1300 °C conditions, employing the temperature gradient growth (TGG) method. All of the obtained crystals displayed the sharp Raman spectra at 1331 cm−1. The photoluminescence (PL) spectra of the synthetic diamonds showed that there was no signal resulting from the nitrogen vacancy (NV) related color centers. However, the Ni-related PL feature, in particularly, the 793.6 nm (NE8 center) with vibronic structure was noticed. Furthermore, Fourier transform infrared (FTIR) measurements indicated that hydrogen (H) impurity was incorporated into the obtained crystals and the characteristic absorptions located at 1405 cm−1, 2800 cm−1 and 2920 cm−1, respectively. Most interestingly, the synthesized diamond crystals did not contain the single substitutional N atoms (C-center), but only the aggregation N impurity occupied diamond lattices and the corresponding FTIR absorption peak located at 1095 cm−1. Hence, this work also provided a new way of thinking for the preparation of diamond, which contained only the aggregation N defects.