Lab Notes

Large Pinkish Orange CVD Synthetic Diamond


5.01 ct pinkish orange CVD synthetic diamond
Figure 1. This CVD-grown diamond, weighing 5.01 ct and Fancy Intense pinkish orange in color, stands out among all CVD synthetics GIA has tested so far. Photo by Jianxing (Jae) Liao.

Natural diamonds with intense pink-orange color are very rare, particularly in large sizes. GIA’s New York lab recently tested a pinkish orange CVD synthetic diamond, submitted by Unique Lab Grown Diamond Inc. in New York, that showed some outstanding gemological features.

This square cut weighed 5.01 ct (9.45 × 9.10 × 6.05 mm) and was color graded as Fancy Intense pinkish orange (figure 1). The color was distributed evenly throughout. A few small feathers and pinpoints were observable under the microscope at about 20× magnification, and the clarity was equivalent to SI1. Infrared absorption spectroscopy revealed this was a type IIa diamond, with nitrogen concentration below the instrument’s detection limit. A clear and sharp peak detected at 3123 cm–1 is a well-known specific feature of CVD synthetic diamond. The absorption spectrum in the UV-Vis region indicated that the observed bodycolor was caused by a very strong and broad absorption band around 520 nm (figure 2). This band can be introduced to a CVD diamond during its growth. It creates a color effect similar to the one from the ~550 nm band in natural pink diamonds. There is no report of the ~520 nm band being introduced to a CVD synthetic diamond after its initial growth. In photoluminescence spectroscopy, clear emissions at 737 nm from SiV– and 503 nm from the H3 defect were recorded. In addition, strong emissions at 575 and 637 nm from NV centers were detected. As a result, this synthetic diamond showed strong orange-red fluorescence in DiamondView imaging. Unlike other large CVD-grown diamonds, this diamond’s fluorescence images hardly revealed the multiple growth layers responsible for its significant thickness. Instead, the multiple growth layers with subtle boundaries could only be detected in high-resolution cathodoluminescence (CL) images.

UV-Vis spectrum of 5.01 ct pinkish orange CVD synthetic diamond
Figure 2. The UV-Vis spectrum of this CVD synthetic revealed that its intense pinkish orange bodycolor was caused by a strong and broad absorption band around 520 nm.

Based on all spectroscopic features, we believe that this CVD synthetic diamond was not treated by HPHT annealing after its growth for color improvement, though heating to a moderate temperature could not be entirely ruled out. The combination of size, color, and clarity made this the most remarkable CVD synthetic diamond GIA has tested so far.

Wuyi Wang is vice president of research and development, and Tom Moses is executive vice president, chief lab and research officer, at GIA in New York.