Summer 2010

Featured Lab Note: CVD Synthetic Diamond Over One Carat

Single-crystal synthetic diamonds grown by chemical vapor deposition (CVD) are occasionally submitted to the GIA Laboratory for identification and grading reports. For the first time, the New York laboratory has identified a near-colorless CVD synthetic diamond larger than one carat that was submitted for grading.

The 1.05 ct pear shape (9.81 × 5.95 × 3.06 mm) was color-graded as equivalent to G. In addition to pinpoint inclusions, it contained some feathers and fractures along the girdle, and its clarity grade was equivalent to I1. No fluorescence was observed when it was exposed to conventional long- and short-wave UV radiation. The mid-IR absorption spectrum showed no absorption in the one-phonon region and no hydrogen-related absorption, which classified it as type IIa. (It is unusual to encounter a “white” CVD-grown diamond without H-related absorption at 3123 cm⁻¹.) Images taken with the DiamondView showed strong pink fluorescence with some irregularly shaped areas of blue fluorescence. PL spectra collected at liquid-nitrogen temperature with laser excitations from the UV to IR regions revealed features typical of CVD synthetic diamond: strong emissions from NV centers, a doublet at 596.5 and 597.1 nm, and [Si-V]⁻ doublet emissions at 736.6 and 736.9 nm. The gemological and spectroscopic features confirmed that this sample was a CVD synthetic diamond.

It is clear that larger, better-quality CVD synthetic diamonds are being produced as there is continued improvement in the growth techniques.

Wuyi Wang and Kyaw Soe Moe