DiamondView imaging of this round brilliant showed an overall orangy-pink to pinkish-orange fluorescence with irregular blue zones, similar to the pattern reported previously for CVD synthetic diamonds. Photo by K. M. Chadwick.

Synthetic diamonds grown by the chemical vapor deposition (CVD) technique have been discussed in several Gems & Gemology articles, most recently the update on Apollo CVD synthetic diamonds by W. Wang and coauthors that was published in the Winter 2007 issue. They have rarely, however, been encountered in the day-to-day grading operations of the Laboratory.

Recently, the Carlsbad Lab identified a near-colorless CVD synthetic diamond weighing approximately one-third of a carat that had been submitted for a standard GIA Diamond Dossier^® grading report. This round brilliant is the first CVD product submitted to the Carlsbad Lab for a grading service. Previously, all of the CVD samples examined in Carlsbad were received directly from the manufacturer for research purposes.

Growth of synthetic diamonds via the CVD method can be accomplished at relatively low pressures, in contrast to the more extreme requirements for growth of high pressure/high temperature (HPHT) synthetics. During CVD growth, gaseous interactions result in deposition of synthetic diamond onto a suitable substrate; single-crystal synthetic diamond is the substrate typically used for production of gem-quality material. Element Six of the United Kingdom and Apollo Diamond Inc. of Boston are two well-known producers of gem-quality CVD materials.

Microscopic examination of the sample submitted for grading revealed numerous feathers and related cavities on the pavilion, which resulted in a clarity grade that fell into the Slightly Included (SI) range. Pinpoints were also observed. Under cross-polarized light, the synthetic diamond showed unevenly distributed, high-order strain colors—the first of many similarities we encountered between this sample and those discussed in the 2007 Wang et al. article.

It exhibited no visible fluorescence to either long- or short-wave UV radiation emitted by a desk-model UV lamp; however, when subjected to the stronger ultra short-wave UV emissions of the Diamond Trading Company DiamondView, it showed an overall strong orangy-pink to pinkish-orange fluorescence (typical of CVD synthetic diamonds), interspersed with patches of blue (see figure). When viewed through the pavilion, the fluorescence details became significantly clearer—including red striations that were most prominent in the pink/orange region and concentration of the irregular blue patches toward the culet—features that were both described by Wang et al.

Fourier-transform infrared spectroscopy indicated that the synthetic diamond was type IIa, and low-temperature photoluminescence spectroscopy using four different laser excitations revealed a classic CVD signature consisting of peak doublets at 736.6/736.9 nm (due to the silicon-vacancy [Si-V] defect) and at 596/597 nm. While the 596/597 nm doublet is still considered unique to CVD synthetic diamonds, the Si-V doublet has been reported in some rare colorless and near-colorless natural diamonds. Most of the other peaks reported by Wang et al., including the 3H (503.5 nm), were also observed.

Given the many similarities between this synthetic diamond and the Apollo CVD material produced during 2006 and 2007 that Wang et al. studied, it is likely that this sample is from a similar generation. Its submission to the Lab for Diamond Dossier grading confirms that at least some CVD-grown synthetic diamonds are present in the marketplace. Examination by a gemological laboratory remains the most effective way to confidently identify synthetic diamonds.

The sample was returned to the client with a Synthetic Diamond Grading Report and the words "LABORATORY GROWN" laser inscribed on the girdle, as is GIA's standard practice.

Karen M. Chadwick and Christopher M. (Mike) Breeding
GIA Laboratory
Carlsbad, California