Lab Notes Gems & Gemology, Fall 2022, Vol. 58, No. 3

Treated Orange and Pink CVD Laboratory-Grown Diamond

Sally Eaton-Magaña and Paul Johnson

Download PDF
These CVD-grown diamonds underwent multiple treatments to enhance their color.
 
 
Figure 1. These 2.00 ct Fancy Deep orange (left) and 3.00 ct Fancy Vivid orangy pink (right) CVD-grown diamonds were subjected to multiple treatments including HPHT processing, irradiation, and low-temperature annealing to achieve the final color grades. Photos by Diego Sanchez (left) and Sood Oil (Judy) Chia (right).

Recently, GIA received two similarly treated diamonds grown by chemical vapor deposition (CVD): a 2.00 ct Fancy Deep orange and a 3.00 ct Fancy Vivid orangy pink (figure 1). A database search revealed that the Fancy Deep orange was the first CVD-grown diamond with an unmodified orange color ever submitted to GIA. CVD-grown diamonds with an orangy pink color are far more common, and the 3.00 ct sample provided for an interesting comparison. From examination of the visible/near-infrared (Vis-NIR) absorption spectra, both samples had similar features and likely underwent similar treatment processes (figure 2). The subtle differences in relative peak intensities were sufficient to create the distinctly different appearances and color grades.

Spectra comparison reveals similar post-growth treatments and defect centers.
 
 
Figure 2. The 2.00 ct Fancy Deep orange and the 3.00 ct Fancy Vivid orangy pink CVD-grown diamonds underwent similar post-growth treatments and show similar defect centers in their Vis-NIR absorption spectra, including the NV centers, 594 nm, SiV–, and GR1. However, subtle differences in relative defect concentrations lead to their distinct color appearances. Although very small, the GR1 defect was also detected in the absorption spectrum of the 2.00 ct CVD-grown diamond. Spectra are offset vertically for clarity.

The Vis-NIR absorption spectra for both CVD-grown diamonds showed nitrogen vacancy centers (principal absorption for NV0 at 575 nm and NV– at 637 nm), 594 nm peak, and the GR1 center. Both samples also displayed strong absorption of the SiV– center (737 nm). In the Fancy Deep orange sample, the NV centers exhibited lower absorption than in the orangy pink sample and also a slightly greater SiV–-related absorption, which helped shift the transmission window from the red (i.e., pink) toward the orange.

Based on the comparatively low value of the 468 nm emission peak determined by 457 nm photoluminescence spectroscopy, both CVD-grown diamonds showed evidence of high-pressure, high-temperature (HPHT) treatment; they were subsequently irradiated to generate the radiation-related features that included the 594 nm peak and the GR1 center. Irradiation was followed by low-temperature annealing, which was intended to generate additional NV centers without fully annihilating the GR1 center. The 594 nm center is a radiation-related defect in nitrogen-containing diamonds. In the IR absorption spectra of both CVD-grown diamonds, small peaks at 1344 cm–1 were observed. From those peaks, the single nitrogen concentration could be estimated as ~1 ppm (S. Eaton-Magaña and J.E. Shigley, “Observations on CVD-grown synthetic diamonds: A review,” Fall 2016 G&G, pp. 222–245).

Both samples presented red fluorescence when excited by the deep UV wavelengths of the DiamondView, a feature that is consistent with the strong nitrogen-vacancy centers in these CVD-grown diamonds. However, neither sample showed any noticeable photochromic effects from the deep UV exposure, something that can occur in CVD-grown diamonds due to charge transfer of the NV centers or the SiV– centers (S. Eaton-Magaña et al., “Laboratory-grown diamond: A gemological laboratory perspective,” Journal of Gems and Gemmology, 2021, Vol. 23, No. 6, pp. 25–39).

The Fancy Deep orange sample was interesting to observe, as unmodified orange colors are extremely rare among natural diamonds and, until now, laboratory-grown samples. Subtle engineering of defect concentrations during post-growth treatment can lead to vastly different results in the color grades.

Sally Eaton-Magaña is senior manager of diamond identification at GIA in Carlsbad, California. Paul Johnson is manager of analytics at GIA in New York.