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Chemical vapor deposition (CVD) growth technology has recently experienced remarkable advancements. In this study, we thoroughly analyze the largest CVD gem diamond encountered by the Gemological Institute of America (GIA) in its Hong Kong laboratory. This exceptional emerald-cut diamond, weighing an impressive 34.59 carats, was produced by Ethereal Green Diamond in India. Its measurements were recorded as 24.94 × 13.95 × 9.39 mm, exhibiting G color and VS2 clarity. The diamond displayed minute black graphite inclusions, some appearing individually within the body, while others formed clusters within growth layers. Let's find out about the diamond blog through the article below.

Microscopic Observations

A close examination of the diamond revealed a distinctive weak oily or wavy graining when observed through the table facet. Such a characteristic is often observed in CVD gem diamonds and becomes more pronounced in diamonds with high strain levels and a strong birefringence pattern. Using crossed polarizers, we observed a high strain and a pronounced birefringence pattern within the diamond.

Microscopic Observations

Spectroscopic Analysis

Infrared absorption spectroscopy was performed to gain further insights into the diamond's properties. The results indicated the absence of absorption related to nitrogen, aligning with the diamond's classification as a type IIa diamond. However, a weak absorption peak was detected at approximately 2800 cm^–1, corresponding to approximately two parts per billion boron impurity (ppb). This trace amount of boron was likely incorporated as contamination during the diamond's growth. The classification of such trace contamination within diamonds remains a topic of debate within the industry.

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Photoluminescence (PL) spectroscopy, conducted at a temperature of –196°C, revealed noteworthy findings. Strong emissions from NV0 and NV– centers at 575 nm and 637 nm were observed, along with moderately strong doublet emissions from SiV– at 736.6 and 736.9 nm. A weak emission at 946.4 nm, possibly originating from the SiV0 defect, was also detected. Other important emission features included a strong emission from the H3 defect at 503.2 nm and a weak emission band with peaks at 566.0, 566.7, and 567.7 nm. Notably, emissions at 596/597 and 467.6 nm, typically found in as-grown CVD diamonds, were diminished due to high-temperature treatment. These spectroscopic observations confirmed that the CVD diamond underwent annealing under high pressure and high temperature (HPHT) to enhance its color appearance. It is worth mentioning that no post-growth color treatment was applied to a 16.41-carat CVD lab-grown diamond analyzed in the New York laboratory a year prior (W. Wang et al., "New record size for CVD laboratory-grown diamond," GIA Research News, January 27, 2022).

DiamondView Imaging and Growth Steps

DiamondView Imaging and Growth Steps

The diamond underwent DiamondView fluorescence imaging, which revealed distinctive green and blue colors with a banded pattern. This pattern indicates typical CVD growth striations, clearly visible within the diamond. The green fluorescence observed was attributed to the H3 defect resulting from HPHT annealing. Furthermore, the imaging unveiled a banded structure consisting of at least eight discernible growth steps, demonstrating the extensive growth required to achieve the significant depth of this large diamond. Intense blue phosphorescence with a similar banded pattern was also detected in the DiamondView images.

The examination of this extraordinary 34-carat CVD diamond represents a remarkable milestone in advancing CVD growth technology. In comparison, naturally mined diamonds of this size and quality are exceedingly rare. As technology continues to evolve, GIA laboratories need to remain vigilant and adaptable in identifying and analyzing gem diamonds. By closely monitoring the developments in gem diamond growth, we can ensure accurate and comprehensive assessments of all diamonds that pass through our laboratories. We hope the information diamond trends jewelry brings you is beneficial.