Spectroscopic Characteristics and Identification Methods of Color-Treated Purplish Red Diamonds
YE Shuang1, CHEN Mei-hua1*, WU Gai2, HE Shuang1
1. Gemmological Institute, China University of Geosciences (Wuhan), Wuhan 430074, China
2. School of Power and Mechanical Engineering, Wuhan University，Wuhan 430072，China
Abstract：Based on the analysis of the spectral characteristics of round faceted color-treated purplish-red diamonds from the domestic market, the identification of this kind of diamonds is confirmed. The sample diamonds are purplish-red with different saturation, and the specific gravity of the hydrostatic weighing method is 3.52. Magnification observation shows that partial facets with the weaker luster of DR-2 and DR-3 have ablative areas that are not re-polished, and graphitization is also obvious along with internal stress fracture, both indicating that samples have been treated with high temperature and high pressure. Under the long-wavelength ultraviolet of 365 nm, the chalky fluorescence appearance of blue, orange-red, yellow and green is mixed, and the phosphorescence phenomenon is absent, which is different from the blue fluorescence or no fluorescence phenomenon of nature-colored purplish-red diamonds. Under GV5000, orange-red and blue mixed fluorescence is observed, and the phosphorescence phenomenon is absent. In the mid-infrared spectra, A center and B center, which show aggregation nitrogen correlation, are classified into IaAB type and have characteristic peaks related to H1a radiation annealing, while in the near-infrared spectra, characteristic peaks of H1b, H1c related to irradiation annealing and characteristic peaks of H2 center are shown. UV-VIS-NIR spectra shows obvious NV-, H2 and 806 nm absorption peak; 400～460 and 570 nm broadband reflectivity changes are associated with N3 and NV0 respectively. Obvious NV- is rarely found in natural purplish-red diamonds and H2 indicates diamonds may be treated with high temperature and high pressure. Furthermore, the low absorption of red light and blue light results in purplish-red appearance. Three-dimension fluorescence spectra and photoluminescence spectra show that N3, H3, H4, NV0 and NV- luminescence centers. N3 contributes blue fluorescence, H3 and H4 contribute yellow-green fluorescence, and NV0 and NV- contribute orange-red fluorescence. According to the comprehensive analysis, the three samples are all diamonds of natural origin that have undergone multiple treatments such as high temperature and high pressure, irradiation and annealing, etc., and the purplish-red color is mainly due to the joint contribution of N3, NV0 and NV-.
Key words：Purplish red diamond; Spectroscopic characteristic; Irradiation and annealing; High temperature and high pressure treatment; NV center
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