Lab Notes Gems & Gemology, Winter 2018, Vol. 54, No. 4

Gemological Analysis of Lightbox CVD-Grown “White” Diamonds

CVD-grown diamond with an internal inscription of the Lightbox logo
Figure 1. The 0.26 ct near-colorless CVD-grown diamond (left) has an internal inscription showing the Lightbox logo, composed of dual narrow lines. The logo is easily detected with a microscope (center) and clearly visible in the DiamondView image (right), in which the red fluorescence is due to nitrogen-vacancy centers. Also seen in the DiamondView image are subtle striations, additional evidence of the CVD origin. The outer square of the Lightbox logo measures 300 microns on each side. Photos by Robison McMurtry (left) and Sally Eaton-Magaña (center and right).

Lightbox, a De Beers company, has begun selling “white,” pink, and blue CVD laboratory-grown diamonds at a flat rate of $800 per carat. Through a third-party vendor, we recently had the opportunity to examine two such samples (0.24 and 0.26 ct) intended for setting in a pair of earrings. Both were near-colorless with color grades equivalent to G color and cut grades of Excellent and Very Good, respectively.

Both lab-grown diamonds had very few clarity characteristics. The 0.24 ct sample had a pinpoint in a bezel facet, and the 0.26 ct round (figure 1, left) had a feather in a star facet, both with VVS clarity. However, the grade-setting feature for both was the Lightbox logo, internally inscribed underneath the table facet (figure 1, center). As a result of the Lightbox mark, the clarity grade for both was reduced to VS. The laser-inscribed internal feature is reportedly made using technology developed by Opsydia (Gem and Jewellery Export Promotion Council, “De Beers to use Opsydia’s laser tech to inscribe lab-grown diamonds in Lightbox Jewelry,” It is composed of dual narrow lines ~2.5 microns wide with a total area of 300 × 300 microns, positioned about 200 microns below the table surface.

Spectroscopic analysis showed both samples had very similar features that were consistent with previ­ously analyzed CVD products from other manufacturers. IR absorption spectroscopy confirmed these samples as type IIa with no detectible single nitrogen at 1344 cm–1. Photoluminescence (PL) spectra showed that both had the 596/597 nm doublet, indicating that they were as-grown and not subjected to post-growth HPHT processing (S. Eaton-Magaña and J.E. Shigley, “Observations on CVD-grown synthetic diamonds: A review,” Fall 2016 G&G, pp. 222–245). Faceted, as-grown near-colorless CVD samples are less common since most manufacturers grow CVD layers quickly, but with a brown color, knowing that they can be HPHT treated to improve color appearance after growth. Approximately 75% of the CVD material in this color range examined by GIA has been HPHT treated after growth (S. Eaton-Magaña, “Summary of CVD lab-grown diamonds seen at the GIA laboratory,” Fall 2018 G&G, pp. 269–270).

PL spectrum shows peaks representative of an as-grown CVD sample
Figure 2. This 514 nm PL spectrum collected on the 0.26 ct sample at liquid nitrogen temperature shows strong nitrogen vacancy centers at 575 and 637 nm and the 596/597 nm doublet, evidence of an as-grown CVD sample.

Through crossed polarizers, we observed very low birefringence compared with the majority of CVD-grown diamonds examined. Additionally, both samples showed very strong emission from nitrogen-vacancy centers by PL spectroscopy (figure 2), as well as visible red fluorescence using DiamondView imaging (figure 1, right), but there was no detectable fluorescence with long-wave UV. With careful DiamondView imaging, subtle CVD striations were visible through the table facet. In the DiamondView images, there were no apparent growth interfaces showing multiple growth events, and no apparent seed crystal remnants were observed. Also, PL spectroscopy of both samples showed very weak but detectable silicon-vacancy centers at 736.6/736.9 nm.

The Lightbox CVD lab-grown diamonds, due to their price point and manufacturer, will likely be highly visible in the trade. The pink and blue samples, as evidenced by De Beers’ literature, have an appearance that is unusual among natural-color diamonds and are unlikely to ever be perceived as a natural-color product. However, the colorless Lightbox samples are readily identifiable as CVD-grown diamonds by spectroscopic techniques, DiamondView imaging, and their distinctive internal inscription.

Sally Eaton-Magaña is a senior research scientist at GIA in Carlsbad, California.