Gemstones are a multibillion-dollar industry, with growing markets in countries including China and India contributing to the boom. As demand increases, forecasters anticipate that prices will rise – and boost the prevalence of counterfeit gemstones as a result. Read more to learn how spectroscopy helps identify counterfeits.
There are technical tools to help thwart the counterfeiters. Raman spectroscopy and related techniques are effective for quickly and easily discriminating many natural from artificial stones, nondestructively and with no sample preparation.
Background
Among the most commonly counterfeited and substituted gems are stones such as diamonds, emerald, ruby and jade, and substances such as amber, coral and pearl. Yet all have unique spectral characteristics that can be identified with powerful spectral instrumentation and proven methodologies.
For example, Raman spectroscopy can explore the molecular structure of the gemstone. The spectral fingerprints provided by Raman spectroscopy contain peaks that can be tied to a gemstone’s chemical structure, as well as the trace minerals and inclusions that give stones such as emerald and ruby their distinctive hues.
Luminescence induced by a high-power, short-wavelength light source offers additional information that can be used to authenticate and to detect various gemstone treatments. Natural and synthetic emeralds, for example, have the same chemical structure and therefore identical Raman spectra. Both get their deep green color from the presence of chromium and vanadium ion impurities, but slight differences in the concentrations and presence of other metal impurities affect the intensity and wavelength of the chromium photoluminescence bands, allowing synthetic emeralds to be distinguished from natural types.
There’s more. Raman and photoluminescence measurements performed concurrently using a 532 nm excitation laser can allow gemologists to determine whether coral and freshwater pearls have been dyed to enhance their natural color, which artificially increases their value.