INVESTIGATION OF GEM MATERIALS USING 405NM LASER SPECTROSCOPY

Milliwatt GaN lasers emitting in the 405nm range have been shown to activate luminescence in a number of minerals of interest for petrographic analysis, and the technique for both visible and spectrographic analysis has been described (Barwood, 2012). Gem minerals were also examined using the 405nm laser and were found to produce distinctive spectra that may aid in their identification and characterization. Diamonds from a variety of sources produced distinctive visible luminescent colors composed of broadband emission lines. Emission colors with the 405nm laser were, in order of abundance: Green to greenish-white, yellow, blue and very weak red. Diamonds with visible blue luminescence showed overlapping lines at 440nm, 450nm and 480nm. Diamonds with visible green luminescence showed a single broad peak at 520nm. Diamonds with visible yellow luminescence had a single broad peak at 560nm. Diamonds with weak visible red luminescence had broadband lines at 510nm and 690nm. Visible green luminescence was the most common luminescent color in the diamonds examined. The laser also activated a number of emission lines in other gem materials. Cr ³⁺ activation was common in beryl var. emerald, corundum, spinel, kyanite, grossularite var. tsavorite, topaz, spodumene var. hiddenite and chrysoberyl var. alexandrite. Mn²⁺ activation was found in apatite, kyanite, spodumene var. kunzite, grossularite, titanite and zoisite var. tanzanite. Sm³⁺ and Dy³⁺ activation were found in apatite, titanite and scheelite. Fe³⁺ activation was rare and noted only in kyanite and some feldspars. The sodalite group, scapolite, axinite and the cancrinite group also showed distinctive yellow to red visible emissions and unassigned broadband spectra. Green Uranium activation was noted in many specimens of opal and chalcedony. Overlapping Uranium lines of unassigned oxidation state were found at 508nm, 527nm, 547nm and 575nm in hyalite opal. Organic gems such as amber, various types of shell material and petroleum inclusions in otherwise non-responsive minerals such as quartz showed moderate to strong visible greenish emissions. Organic emission spectra, while variable, were very asymmetrical, broadband and centered on 510nm.