All rights reserved. Intellectual Property: Gemological Institute of America
Single-crystal CVD* synthetic diamonds are occasionally submitted to the GIA Laboratory for identification and grading reports. For the first time, the New York lab has identified a near-colorless CVD-grown diamond larger than a carat that was submitted for grading.
This 1.05 ct pear shape (9.81 x 5.95 x 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 infrared absorption spectrum indicated that the sample was type IIa. Images taken with the DiamondView, which employs strong ultra short-wave UV radiation, showed strong orange-red fluorescence with some irregularly shaped regions of blue fluorescence. Photoluminescence spectra collected at liquid-nitrogen temperature with laser excitations from the UV to IR regions revealed features typical of a CVD synthetic diamond, and this identification is consistent with its other properties.
Clearly, CVD synthetic diamonds of better quality and size are being produced as the growth techniques continue to improve.
Wuyi Wang and Kyaw Soe Moe
GIA Laboratory, New York
* CVD stands for Chemical Vapor Deposition, a chemical process used to produce high-purity, high-performance solid materials. The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 methane to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser. This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).