Lab Notes Gems & Gemology, Winter 2020, Vol. 56, No. 4

Largest CVD Laboratory-Grown Diamond Submitted to GIA

M-color CVD-grown diamond weighing 7.07 ct.
Figure 1. This M-color, 7.07 ct round brilliant is the largest CVD-grown diamond seen to date at GIA. Photo by Diego Sanchez.

Chemical vapor deposition (CVD) diamond growth has greatly improved over the years. More CVD-grown diamonds are seen in the market today, and in recent years, larger CVD-grown diamonds are beginning to emerge. In 2016, the GIA laboratory in Hong Kong examined a 5.19 ct cushion, the largest CVD-grown diamond analyzed at GIA until now (Winter 2016 Lab Notes, pp. 414–416).

A larger CVD-grown diamond was recently submitted to the GIA laboratory in Carlsbad: a round brilliant with VS2 clarity and M color weighing just over 7 carats (figure 1). This 7.07 ct CVD-grown diamond came to the Carlsbad laboratory undisclosed as CVD, but advanced testing correctly identified this diamond’s origin. The largest reported faceted CVD-grown diamond is a 12.75 ct round brilliant (“IGI’s Hong Kong lab certifies largest CVD grown diamond,” IGI Press Room, November 23, 2020).

This diamond exhibited peaks typical of CVD-grown diamonds.
Figure 2. The photoluminescence spectrum collected with a 514 nm laser at liquid nitrogen temperature reveals the NV centers and silicon-vacancy center that are typically observed in CVD-grown diamonds.

Microscopic investigation revealed grade setting graphitic inclusions just below the center of the table. Photoluminescence investigation showed characteristic growth features consistent with a CVD-grown diamond that was subsequently HPHT-treated, generally intended to reduce the brown coloration. With 514 nm excitation at liquid nitrogen temperature (–196°C), nitrogen-vacancy centers at 575 [NV]0 and 637 [NV] nm, along with a strong [SiV] doublet at 736.6/736.9 nm were revealed (figure 2) determining this diamond as CVD-grown. When viewed through the DiamondView, growth layers were evident (figure 3), 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 (figure 3; Wang et al., “CVD synthetic diamonds from Gemesis Corp.,” Summer 2012 G&G, pp. 80–97).

Striations are diagnostic of a CVD origin.
Figure 3. DiamondView fluorescence imaging shows the striations that are diagnostic of its CVD origin, and its coloring is consistent with post-growth HPHT treatment. Image by Adam Steenbock.

CVD-grown diamonds of these sizes are still a rarity, but with new technologies and advancements it is evident that larger laboratory-grown diamonds are becoming more prevalent.

Garrett McElhenny is a research technician, and Sally Eaton-Magaña is senior manager of diamond identification, at GIA in Carlsbad, California.