Synergistic effect of nitrogen and hydrogen on diamond crystal growth at high pressure and high temperature

• C3N6H6 as additive under high pressure and high temperature.
• Hydrogen–nitrogen co-doped diamonds were synthesized.
• The simultaneous incorporation of nitrogen and hydrogen plays an important role in the synthesized diamond.
• The possible incorporated route is introduced for the crystallization diamond with the simultaneous incorporation of nitrogen and hydrogen

Diamond crystals co-doped with nitrogen and hydrogen atoms are successfully synthesized in the metal–carbon system with melamine (C3N6H6) additive in a series of experiments at temperatures of 1200–1740 °C and pressures of 5.0–6.0 GPa. Experimental results show that the crystallization of our obtained diamonds changes significantly, which is attributed to the simultaneous incorporation of nitrogen and hydrogen into the diamond crystal structure. IR measurement shows that the intervention of hydrogen effectively changes the nitrogen concentration and substitutional form, accompanied by a non-uniform distribution of nitrogen and hydrogen in the synthesized diamond. Raman measurement indicates that such non-uniform distribution of nitrogen and hydrogen in the synthesized diamond leads to the change of internal structure of diamond crystals. For the crystals co-doped with hydrogen and nitrogen, a special feature of photoluminescence spectroscopy is typically observed at 536 nm. Base on our results, a possible incorporated route is introduced for the crystallization diamond with simultaneous incorporation of nitrogen and hydrogen.