Lab Notes Gems & Gemology, Spring 2016, Vol. 52, No. 1

Ring with a CVD Synthetic Melee Diamond

CVD synthetic melee diamond mounted in ring
Figure 1. One of the round-cut melee mounted in this ring was identified as a CVD synthetic diamond. Photo by Johnny Leung.

The separation of synthetic diamond melee from natural diamond melee is a significant concern. Some specimens have been identified by GIA and other laboratories as synthetic, but those products were predominantly HPHT grown. GIA’s Hong Kong lab recently identified a CVD synthetic melee mounted in a ring (figure 1).

The round-cut synthetic measured approximately 2.8 mm in diameter and weighed about 0.08 ct. Color could not be graded due to the mounting, but it was estimated to be in the F-H range. The material showed no notable visual features using the microscope other than a small surface scratch at the table. Infrared absorption spectroscopy indicated the typical features of a type IIa diamond; no defect-related absorption feature was detected. A PL spectrum was collected at liquid nitrogen temperature with a very wide range of laser excitation wavelengths. Major features included emissions from [N-V] and [Si-V] centers (figure 2). The emission at 575.0 nm from [N-V]0 is much stronger than the peak at 637.1 nm from [N-V], similar to many natural type IIa diamonds. Most notably, this specimen showed very strong emissions at 736.6 and 736.9 nm from the [Si-V] defect. Using 514 nm laser excitation, the intensity of the [Si-V] defect was about eight times that of the diamond Raman line. DiamondView imaging revealed strong orange color with small irregular areas of blue fluorescence (figure 3). All these observations confirmed that this melee is an as-grown CVD synthetic.

Photoluminescence spectrum of melee diamond
Figure 2. The photoluminescence spectrum collected at liquid nitrogen temperature with 514 nm laser excitation shows moderate emissions from [N-V] centers and a very strong emission from [Si-V].
DiamondView of CVD synthetic melee diamond
Figure 3. DiamondView imaging showed strong orange fluorescence with small irregular areas of blue fluorescence, a typical feature of as-grown CVD synthetic diamond. Photo by Carmen Lo.

This was the first mounted CVD synthetic melee diamond identified by GIA. While synthetics of this size are overwhelmingly HPHT grown, we do expect to see more CVD synthetic diamond melee in the future.

Terry Poon is a supervisor in the diamond identification department, and Carmen Lo and Billie Law are diamond graders, at GIA in Hong Kong.