Labs Identify GE/POL Traits

April 25, 2000

Labs Identify GE/POL Traits

De Beers scientists in England and South Africa discovered a quantifiable way to identify GE/POL diamonds using spectroscopic techniques to find nitrogen vacancy centers in the treated diamonds. The research was published this week in the Spring 2000 issue of Gems & Gemology, the Gemological Institute of Americas quarterly journal. Separately, the SSEF Gemmological Laboratory, Basel, Switzerland, announced a new routine service to identify GE/POL treated diamonds based on its study of treated and untreated diamonds, which will be published this spring in European gemological journals. The SSEF study also depends on the identification of nitrogen vacancy centers.

The De Beers study examined 39 treated and 30 non-treated Type IIa diamonds. The study reported spectroscopic observation of luminescence peaks using laser excitation of cryogenically cooled diamonds. (Cooling, usually with liquid nitrogen, helps define absorption patterns). Specifically, De Beers scientists observed excitation peaks at 575 and 637 nanometers in most of the GE/POL diamonds studied. The peaks result from nitrogen vacancy centers, which are a single nitrogen atom in a vacancy. Normally, Type IIa diamonds have little or no nitrogen; the presence of nitrogen in the GE/POL diamonds is what makes them treatable.

De Beers is working with several laboratories to develop a practical way to apply its research. Raman spectrometers, used in combination with cooled diamonds and laser excitation, could record the differences and make determinations. According to GIA, the authors say a majority of GE/POL diamonds will be identifiable when their spectral features are combined with the GE/POL characteristics observed by microscope in an earlier GIA study (Fall 1999 Gems & Gemology). De Beers research into the GE/POL process is part of its Gem Defensive Program.

The SSEF Web site says its identification is essentially based on laser-induced fluorescence spectroscopy performed on a Raman system at liquid nitrogen temperature. SSEF says it observed a luminescence pattern that proves the presence of a small number of nitrogen vacancy centers in all the GE/POL treated diamonds it studied. None of the non-treated stones SSEF studied showed the nitrogen vacancy centers.

On a practical level, identification of GE/POL diamonds using these kinds of tests will not be done by retailers, since the equipment needed to do the job is beyond the reach of conventional gemology and prohibitively expensive.

GE's reaction to the latest news? "The study and tests are encouraging," says Dr. Thomas Anthony, the GE staff physicist who developed the GE/POL treatment. "The test is reliable for the lower colors of diamonds J-Z stones because they contain nitrogen. But it's not reliable for higher colors or clean diamonds." [Note: For diamonds without nitrogen, examination of inclusions and how they react under HPHT may be needed. In this case, a D-flawless GE/POL diamond would not be as easily detected.] "In terms of dollar value, on a piece-by-piece basis, 90% of the stones are still undetectable," says Anthony. He says GE researchers are studying detection methods also, but that a 100% solution has eluded them so far.

For copies of the Spring 2000 Gems & Gemology, call (800) 421-7250, ext. 7142; e-mail dortiz@gia.edu, or go to www.gia.edu/gandg/index.cfm. For more information on the SSEF labs study, go to www.ssef.ch. (Click on Info, then News.)

- by Robert Weldon, G.G.