Professional Jeweler Archive: Zeroing in on GE/POL Identification

July 2000


Zeroing in on GE/POL Identification

A Swiss lab says there’s a new way to detect nitrogen in Type IIa diamonds. This appears to be the key in identifying GE/POL diamonds

New information about the presence or absence of nitrogen in diamonds has propelled one major gemological laboratory to offer identification services for GE/POL diamonds independent of girdle inscriptions. The discovery by the SSEF Gemmological Laboratory in Basel, Switzerland, and similar findings by scientists around the world, suggest a review or clarification of the definition of Type IIa diamonds may be necessary.

Nitrogen Vacancy Centers

Until now the gemological community has believed the very rare Type IIa diamonds contain negligible amounts of nitrogen atoms or none at all. But new research by SSEF, in collaboration with a scientist at the University of Nantes in Nantes, France, found virtually all the untreated Type IIa brownish diamonds examined show the presence of nitrogen vacancy (or N-V) centers. An N-V center occurs when a nitrogen atom is present in the diamond’s structure, linked to a vacancy in the diamond lattice.

“The discovery of N-V centers in Type IIa diamonds is not really new,” says Emmanuel Fritsch, physics professor and gemologist at the University of Nantes. “What is new is the use of photoluminescence spectroscopy to detect a treatment in these diamonds [such as the high-pressure/high-temperature annealing involved with the GE/POL treatment].”

Technology to the Rescue

While the presence of N-V centers has been known for some time, detecting them was another matter. “A conventional way for scientists to test for nitrogen is by using infrared spectroscopy,” says SSEF Director Henry Hänni. “But with infrared spectroscopy, minute or negligible amounts of nitrogen were not detectable, which skewed the understanding of Type IIa diamonds. But with the more sensitive analytical methods of photoluminescence spectroscopy, using either De Beers’ heavy equipment or the more convenient beam from a Raman spectrometer, the N-V centers can now be detected.”

Fritsch says that because all GE/POL diamonds are essentially annealed Type IIa, differences between treated and natural ones will be slight. “All we can hope for is a small concentration of specific defects revealing the presence of a treatment,” he says. “Photoluminescence is little used in gemology because most labs don’t have luminescence spectrometers. But a Raman spectrometer laser, now found in many labs, can be used to excite luminescence.”

Hänni says the presence of N-V centers in luminescence spectra is indicated by two peaks: 575 nanometers and 637 nanometers. A study of these peaks and their intensity helps determine whether diamonds have been treated.

The new technology has prompted SSEF to offer a service determining whether a Type IIa diamond has been treated. SSEF notes other gemological methods are used in combination to prove treatment.

Further Review

Hänni discussed the various methods used at SSEF during a presentation at the JCK International Jewelry Show in June in Las Vegas, NV. He and his associates also will prepare a follow-up article on the subject. A review of the methodology will appear in the August issue of Professional Jeweler.

The recent findings by SSEF and similar findings by De Beers may solve the frustrating identification mystery that’s enveloped GE/POL diamonds since Pegasus Overseas Ltd., a subsidiary of Lazare Kaplan International, New York City, announced last year it would market diamonds whose color had been improved by a proprietary process developed by General Electric.

– by Robert Weldon, G.G.

GE/POL diamonds can be identified by the laser inscription engraved on the diamond’s girdle. Technological advances in gemology make it possible to identify the diamonds even if the laser inscription is removed.

Copyright © 2001 by Bond Communications