The 2020 Winter Editioin of GIA’s Quarterly Journal, “Gems & Gemology” reports of the submissiion of a round brilliant-cut, VS2 clarity, M-color diamond weighing 7.01 carats for grading, which on examination turned out to be a CVD lab-grown diamiond, the largest such diamond submitted to the Carlsbad Laboratory for identification and grading. The diamond was submitted undisclosed as CVD, but advanced testing carried out by the lab, correctly identified the origin of the diamond.
The Photoluminescence Spectrum obtained using a 514 nm laser, at liquid nitrogen temperature revealed NV centers and Silicon Vacancy centre at wave lengths consistent with CVD-grown diamonds. With 514 nm excitation at liquid nitrogen temperature (–196°C), Nitrogen Vacancy centers at 575 [NV]° and 637 [NV]– nm, along with a strong [SiV]– doublet at 736.6/736.9 nm were revealed determining this diamond as CVD-grown.
When viewed through the Diamond View, growth layers were evident, diagnostic of diamonds of CVD origin, and the green fluorescence along with the lack of a 596/597 nm feature in the PL spectrum were indicative of post-growth HPHT treatment.
HPHT treatment of CVD diamonds are usually resorted to reduce the brown coloration of CVD diamonds.
The largest reported faceted CVD-grown diamond was a 12.75 Ct, Type Iiia, F-color, VVS2-clarity round brilliant-cut diamond submitted to the International Gemological Institute, Hong Kong Branch, for grading by the Chinese Manufacturer, Shanghai Zhengshi Technology. on November 23, 2020.