Lab Notes Gems & Gemology, Summer 2020, Vol. 56, No. 2

Irradiated Blue Diamond with Interesting DiamondView Image

Artificially irradiated Fancy Deep greenish blue diamond weighing 1.00 ct.
Figure 1. This 1.00 ct Fancy Deep greenish blue diamond (left) owes its color to artificial irradiation, which is also evidenced by the color concentration at the culet (right). Photos by Diego Sanchez (left) and Sally Eaton-Magaña (right).

We often receive lab-irradiated diamonds at the laboratory that have either natural or laboratory-grown origins (e.g., Summer 2018 Lab Notes, pp. 215–216). However, we recently received a 1.00 ct Fancy Deep greenish blue irradiated diamond (figure 1) with some unusual gemological features. The diamond’s spectra and imaging showed that it had received artificial irradiation likely followed by annealing, which created unusually high concentrations of nitrogen vacancy (NV) centers.

DiamondView fluorescence images of the irradiated blue diamond.
Figure 2. The DiamondView fluorescence images of the irradiated diamond collected from the pavilion (left) show a high concentration of NV centers creating the orange fluorescence. On the table (right), the NV concentration has decreased sufficiently so that the NV-related orange fluorescence transitions to the diamond’s intrinsic blue fluorescence. Images by Sally Eaton-Magaña.

As with most lab-irradiated diamonds, it was irradiated with the table side down; thus, the culet facing the beam received the highest dose of irradiation while much of the table facet was comparatively protected. The irradiated pavilion shows orange fluorescence due to a high concentration of NV centers (figure 2, left). Irradiated diamonds are often subjected to some low-temperature annealing after irradiation in order to “stabilize” the defects (e.g., Spring 2018 Gem News International, pp. 105–107); however, we generally do not see evidence of NV centers forming from that low-temperature heating.

Here we see a combination of treatment conditions that generated an NV-related fluorescence on the pavilion and the crown; however, the original blue fluorescence of the natural, pre-irradiated diamond persists on the table, which was “shielded” during the irradiation (figure 2, right). The table experienced a lower radiation dose, fewer NV centers formed as a result, and we observe a transition from the orange NV fluorescence to the intrinsic blue fluorescence. Thus, the DiamondView fluorescence collected from the table creates an intriguing image.

The combination of the intrinsic defect concentrations along with the specific irradiation dose and subsequent annealing conditions created an unusual treated diamond for scientific study and an interesting reinterpretation of a “nailhead” diamond—a term often applied to a poorly cut stone that is dark on the table. Here, this effect can only be revealed under UV illumination.

Sally Eaton-Magaña is senior manager of diamond identification at GIA in Carlsbad, California.