Lab Notes Gems & Gemology, Winter 2014, Vol. 50, No. 4

CVD Synthetic Diamond with Fancy Vivid Orange Color

CVD synthetic diamond
Figure 1. This 1.04 ct round was identified as a CVD synthetic diamond. Its Fancy Vivid pinkish orange color was introduced through post-growth irradiation and annealing. Photo by Sood Oil (Judy) Chia.
With the rapid improvement of CVD synthetic diamond quality in recent years, various colorations can be introduced after growth. The New York laboratory recently tested a CVD synthetic with a very attractive orange color.

This round-cut specimen weighed 1.04 ct and was color graded as Fancy Vivid pinkish orange (figure 1), a very rare color among natural and treated diamonds. Except for a few dark pinpoint inclusions, it showed no notable internal features. Under crossed polarizers, it displayed natural-looking “tatami” strain patterns. Absorption spectroscopy in the infrared region showed typical type IIa features, with no detectable defect-related absorption. At liquid-nitrogen temperature, a few absorption features were detected in the UV-Vis-NIR region (figure 2). The major ones include absorptions from N-V centers with ZPL at 575.0 and 636.9 nm, and their related side bands. We also recorded absorptions from some irradiation-related defects, including 594.4 nm, GR1 at 741.2 nm, ND1 at 393.4 nm, and the general radiation absorption features at 420–450 nm. Also observed were weak absorptions from the H3 defect at 503.2 nm, possible nickel-related defects at 516.1 nm, and [Si-V] at 736.6/736.9 nm. Under the strong short-wave UV radiation of the DiamondView, the sample showed very strong red fluorescence with sharp linear growth striations, a unique feature of CVD synthetic diamond. Weak red phosphorescence was also detected. These observations confirmed that this was a CVD synthetic diamond with post-growth treatments. Nitrogen concentration, based on absorptions in infrared absorption spectroscopy, was below 1 ppm. After initial growth, the sample was artificially irradiated and then annealed at moderate temperatures to introduce the N-V centers. Strong absorptions from N-V centers are the main causes of the observed pinkish orange bodycolor.

Diamond’s absorption spectrum
Figure 2. Several defects were detected in the CVD synthetic diamond’s absorption spectrum in the UV-Vis-NIR region at liquid-nitrogen temperature. Strong absorptions from the N-V centers are the main cause of the observed pinkish orange color.
The very attractive orange color was achieved by introducing the proper concentrations of N-V centers while limiting the formation of other defects. It should be pointed out that the relatively high concentration of [Si-V] could be attributed to the treatment by combining preexisting Si impurity with artificially introduced vacancies. With further developments in after-growth treatment, it is highly likely that more colors in CVD synthetic diamonds will be introduced.

Wuyi Wang is the director of research and development and Kyaw Soe Moe is a researcher at GIA’s New York laboratory.