HPHT treatment of different classes of type I brown diamonds

The characteristic photoluminescence and EPR features of superdeep diamonds (São-Luis, Brazil)

“…Despite the fact that it is often observed in untreated brown and pink diamond crystals, very few studies have been devoted to it (Gaillou et al 2010;Titkov et al 2008;Tretiakova 2009;Hainschwang et al 2005;Yang et al 2012). According to the present study, the ZPL is accompanied by a vibrational sideband formed via the interaction with 38 and 78 meV phonons close to a quasi-local vibration of a vacancy.…”

“…The center was also frequently detected in transparent colorless Yakutian diamond samples of octahedral habit, which had low nitrogen content in A and B forms and commonly exhibited the 418 nm and GR1 centers (unpublished data of the authors). According to the findings presented in this paper and the previously published data (Hainschwang et al 2005;Tretiakova 2009), the 612.4 nm center is annealed out at temperatures up to 2000 °C. It has been identified as a nickel-containing defect (Lindblom et al 2005).…”

Spectroscopic Characteristics of Treated-Color Natural Diamonds

“…Similarly, the formation of H2 center requires for the existence of the donors (e.g., the C center), and therefore the existence of isolated nitrogen together with H3 and H2 centers is another possible property related to HPHT treatment [55,58]. Although the intensity of the 637 nm is found to be stronger than that of 575 nm for the HPHT-treated diamonds in this work, which is considered to be a typical characteristic of HPHT treatment in previous works [4,49,59,60], however, Collins [34] suggested that it is just a rough criterion and works well for approximately 75% of the HPHT-treated diamonds.…”

“…In addition, when the irradiated type Ia diamonds are subjected to 2300°C at 5.0 GPa, the 637 nm absorption is extremely weak or undetectable [29]. In type Ia brown diamonds, the NV − center was produced by HPHT treatment at 2000°C and above [4,34] and could be rather strong through a few minutes of HPHT treatment at a temperature of 2300°C [45].…”

“…Generally, the gemologists have begun to enhance the color of diamond since the 1930s [2] and diamond treatments in the modern era mostly involve high-energy irradiation, high pressure and high temperature (HPHT) treatment, low pressure and high temperature (LPHT) annealing, and combination of these treatments [3][4][5][6][7][8][9][10][11]. Such as Vins [12] reported that natural diamonds with brown hue could be altered to display purple to red color, through multiprocess treatments including HPHT treatment (6-7 GPa at over 2150°C), high-energy irradiation, and LPHT annealing (lower than 1100°C).…”