Identification of HPHT-treated Hydrogen-rich Diamonds by Optical Absorption and Photo Luminescence Spectroscopy Techniques

Research on different types of brown diamonds under high temperature and high pressure and their structural characteristics is one of the most difficult and important issues in diamond research. Previous studies on hydrogen-rich diamond mainly focused on its special growth structure and the formation environment, but rarely on the characteristics of hydrogen-rich diamond after high temperature and high pressure treatment. The spectral characteristics of the hydrogen-rich diamonds before and after high temperature and high pressure treatment, including Infrared Spectra, UV-vis Absorption Spectra, and Photoluminescence Spectra were compared and their identification characteristics were studied. Results show that the spectroscopic features are different for the samples before and after the high temperature and high pressure treatment, epecially for infrared spectra. Absorption peaks related to H and N at 3310 cm^-1, 3232 cm^-1, 3189 cm^-1 weakened obviously or even disappeared. Moreover, the absorption peak at 2688 cm^-1 related to isolated nitrogen appeared. In the UV-Vis absorption spectrum, the non-selective absorption in treated brown diamonds became the typical isolated nitrogen absorption, which means that the absorption of 550 nm to shortwave and the absorption of the center of N₃ (415 nm) increased obviously. Therefore, the diamond changed from the original brown to yellow. The photoluminescence spectra before and after treatment of diamonds also vary with the types of nitrogen-related defects, peak intensities, and defect combinations. The spectral characteristics obtained not only provide a basis for the accurate identification of yellow, hydrogen-rich diamonds treated by high temperature and high pressure, but also provide a theoretical basis for explaining the change mechanism of hydrogen-and nitrogen-related lattice defects under high temperature.