405 NM LASER LUMINESCENCE SPECTROSCOPY OF NATURAL DIAMONDS

Examination of natural diamonds has shown that many of them luminesce using 405 nm laser diode illumination. Microdiamonds from a variety of sources were examined and produced distinctive visible luminescent colors composed of broadband emission lines. Emission colors observed with the 405 nm laser were, in order of abundance: Green to greenish-white, yellow, blue, and very weak red. The visual and photographic colors are only revealed when the strong violet emission of the laser is blocked with a yellow filter. Diamonds with visible blue luminescence showed overlapping lines at 440 nm, 450 nm and 480 nm. Diamonds with visible green luminescence showed a single broad peak at 520 nm. Diamonds with visible yellow luminescence had a single broad peak at 560 nm. Diamonds with weak visible red luminescence had broadband lines at 510 nm and 690 nm. The red luminescence was a core surrounded by green luminescence and the 510 nm peak was probably from the surrounding green luminescing diamond. Visible green luminescence was the most common luminescent color in the diamonds examined. The response of the diamonds to 405 nm laser light appears identical to emission colors and spectra reported for Cathodoluminescence in diamonds; however, the technique is much simpler to use and may have applications in diamond exploration and analysis.