A SPECTROSCOPIC LOOK AT GREEN AND BLUE GEM DIAMONDS COLORED BY ARTIFICIAL IRRADIATION TREATMENT

Green and blue colored gem diamonds are highly valued and quite popular in the jewelry industry. Naturally colored diamonds in these hues are very rare and expensive because of their rarity, creating a large demand for lower cost treated goods with similar colors. Artificial irradiation treatment, usually done with electrons, can quickly (within a few minutes) produce intense green and blue colors in diamond by displacing carbon atoms in the lattice to create vacancies. This type of diamond treatment has been well known since the 1950s, but the circumstances that yield green versus blue color have not been systematically characterized. Careful examination of 20 diamonds (10 blue, 10 green) that were artificially irradiated by a commercial producer reveals clear differences in absorption and photoluminescence spectra. These differences are caused by variations in nitrogen content and lattice defect configuration (specifically H3, N3, and GR1) and are directly responsible for the blue or green result. In general, diamonds with higher total nitrogen content (56-515 ppm; avg = 260 ppm) became green following treatment and those with lower concentrations (39-288 ppm; avg = 101 ppm) turned to blue. However, many nuances in defect configuration also affected the results. Evaluation of several additional diamonds before and after irradiation treatment allowed for systematic evaluation of the lattice changes caused by the process. This type of analysis is important for gem labs because it is often difficult to distinguish naturally irradiated gem diamonds from artificially produced colors because the color mechanism is similar.