Fancy Deep Brown-Orange CVD Synthetic Diamond
A 0.56 ct diamond (figure 1) was color graded as Fancy Deep brown-orange. The diamond was found to be a CVD-grown synthetic that had been irradiated and annealed, perhaps multiple times. DiamondView imaging (figure 2) showed the telltale striations of the CVD growth process, and the PL spectrum showed the SiV– (736/737 nm doublet) commonly found in CVD synthetics. The Vis-NIR spectrum (figure 3) showed a GR1 defect (the neutral vacancy center) and a peak at 594 nm that is commonly seen in diamonds that have been irradiated and annealed. This is in contrast to the normal irradiated and annealed CVD synthetic diamonds that show features related to nitrogen vacancies. The PL spectrum shows the NV0 (575 nm) and NV– (637 nm) peaks in relatively high concentrations compared to the diamond Raman line. In the infrared spectrum, a clear band at 1130 cm–1 and a peak at 1344 cm–1 indicate the presence of single substitutional nitrogen.
CVD-grown synthetic diamonds have been known to be irradiated (Fall 2014 Lab Notes, pp. 240–241; Fall 2015 Lab Notes, pp. 320–321) and also irradiated and annealed (J. Shigley et al., “Lab-grown colored diamonds from Chatham Created Gems,” Summer 2004 G&G, pp. 128–145). The irradiation and annealing performed on CVD synthetics is generally done on those with isolated nitrogen and produces a pink to red bodycolor. This color is caused by nitrogen-vacancy centers created when the vacancies produced by irradiation combine with the isolated nitrogen during the annealing process. In this case, the diamond showed a brown-orange bodycolor due to the combination of the isolated nitrogen and irradiation features. The stone in question contained isolated nitrogen, so it is possible that the intent was to create a pink to red color, but the treatment did not produce the expected results. Brown-orange color as a result of treatment has not been seen in a CVD synthetic diamond before, so the intentions of the treatment are as yet unknown.