Raman Photoluminescence Spectroscopy

Detecting near-colorless synthetic diamonds may have become easier. A distinctive luminescent band at 693.7 nanometers was discovered in these diamonds using SAS2000 Raman photoluminescence spectroscopy by Marty Haske, president of Adamas Gemological Laboratories, Brookline, MA.

Haske cautions the test is preliminary. "We have only studied a limited sample representing about three years of Russian near-colorless production. Out of a total of 37 diamonds we've studied, 27 showed the distinctive photoluminescence peak," he says. "The existence of the feature is apparently correlated to short-wave fluorescence/phosphorescence present in the near-colorless synthetic diamond samples." Haske's research shows that when he detects fluorescence or phosphorescence he also detects the spectroscopic peak.

Haske says he obtained the near-colorless synthetics from Chatham Inc., San Francisco, CA, and the Morion Co., Brighton, MA. He hopes other synthetic diamond producers such as Sumitomo, General Electric and De Beers will supply his laboratory with samples for further study.

Other labs contacted by Professional Jeweler had mixed responses, but all agree the results are preliminary. SSEF Laboratory, in Basel, Switzerland, says it also detected the feature in some synthetic diamonds, but says it's too early to make a definitive statement. GIA, however, has not detected the feature. "The feature described is not present in the colorless synthetic samples we have observed and would need further investigation to determine its significance with regards to an identification criterion," a GIA spokesperson says. Dr. Emmanuel Fritsch, University of Nantes, France, says he hadn't performed any testing at press time, but appears to approve of Haske's methodology. "It may not be a 100% criterion [for all near colorless synthetic diamonds] but it is a correct observation for many stones of a certain category, so the finding deserves attention," he says. "Providing Marty's work is correct, the 693.7 line is sure a strong indication for synthetic origin."

Several other gemological tools, visual and scientific, are used to detect synthetic diamonds. While most near-colorless synthetics show visual clues, such as metallic inclusions, scientific tests are reserved for those stones that cannot be detected by conventional means. Such tests include electrical conductivity. "All synthetic near-colorless diamonds I have observed to date are electrically conductive when properly tested," says Haske. He says the new Raman spectroscopy test, if confirmed, would greatly simplify and enhance the arsenal of tools needed to detect near-colorless synthetics.