investigation of gem materials using 405nm laser spectroscopy henry barwood troy university troy,...
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Investigation of Gem Materials using 405nm Laser Spectroscopy
Henry BarwoodTroy UniversityTroy, Alabama
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405nm laser diode
GaN diode lasers were developed for Blu-Ray players. They are now widely manufactured in power levels ranging up to 500mW.
Inexpensive diode assemblies are now available in the 5-200mW range, both battery powered (laser pointers) and with AC power supplies and collimating lenses that provide either a spot or line focus.
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5mW 405nm Laser pointer. Inset 150mW Diode
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405 nm laser spectrum
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Spectrometer/Diode holder for spectroscopy of small sample areas
A simple holder was constructed that focuses the laser beam onto a small aperture that is centered on the focus of the spectrometer collimator (UV-NIR). The resultant fluorescence is fed into the spectrometer via a standard fiber optic cable (also UV-NIR).
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Laser Diode and Collimator Holder
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Spectrometer modification
An Ocean Optics HR2000 spectrometer was modified with the addition of a new grating that increased the wavelength range to 200-1100nm.
The 10 micron slit on the spectrometer was replaced with a 100 micron slit to improve light gathering power.
A UV-IR fiber optic cable and collimator were added that allow the full 200-1100nm wavelength range. While stiff, a 200 micron fiber was selected for maximum light transmission.
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Laser imaging for photomicrography
Spot focusing lasers are adaptable for imaging gems, small crystals, or areas of petrographic slides.
The high visible output of the laser must be blocked with a yellow filter before a useful image may be obtained.
Imaging as a substage light source is dangerous, and only incident illumination should be used
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Imaging of Samples with an Un-collimated Laser Beam
The output of a laser diode operated without the collimating lens can be scanned across a specimen while the camera is in Bulb mode. This allows the collection of a macro image of the specimen. By blocking most of the visible light with a yellow filter, minerals having a response to the 405nm laser emissions may be imaged. Processing of the images can also provide a quantitative measure of the amount of the fluorescent mineral.
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• In order to test the laser fluorescence of diamonds, small < 1mm crystals were purchased from a number of sources. No information as to the actual source localities of the diamonds was available; however, they were simply listed as “Congo”. The body colors of the diamonds were mostly yellow to off white.
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DiamondsFluorescent colors observed in diamonds using 405 nm laser
• Green (common)• Yellow ( 5 examples)• Blue (single example)• Red (single example)
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In all subsequent figures, the fluorescent specimen is pasted in the upper right hand corner of the figure
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Blue luminescent diamond spectrum
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Green luminescent diamond spectrum
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Yellow luminescent diamond spectrum
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Red luminescent diamond spectrum
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Gems showing dominant Cr3+ (and Fe3+) response to 405nm laser
• Beryl var. Emerald• Chrysoberyl var. Alexandrite• Corundum var. Ruby• Grossularite var. Tsavorite• Kyanite• Spinel• Spodumene var. hiddenite• Topaz
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Emerald spectrum showing Cr3+ and Fe 3+ (?) activation
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Corundum var. Ruby (synthetic) spectrum showing Cr3+ activation
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Chrysoberyl var. Alexandrite spectrum showing Cr3+ activation
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Grossularite var. Tsavorite spectrum showing Cr3+ and Fe3+ (?) activation
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Comparison of 405nm Spectra forKyanite Color Variations (line colors correspond to blue, green and
orange kyanite). Note Differences in Cr3+ Lines
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Spodumene var. Hiddenite spectrum showing Cr3+ and Fe3+ (?) activation. The green response on the spectrum is from the unknown green luminescing inclusions in the
spodumene
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Topaz (Brazil) spectrum showing Cr3+ and weak Fe3+ (?) activation
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Gems showing dominant Mn2+ activation
• Fluorapatite• Grossularite• Kyanite• Spodumene var. Kunzite• Titanite• Zoisite var. Tanzanite
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Fluorapatite spectrum showing Mn2+
activation
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Grossular (Mexico) spectrum Mn 2+ activation
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Spodumene var. Kunzite spectrum showing Mn2+ activation
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Pink Tanzanite spectrum showing Mn2+ activation
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Gems showing dominant REE activation (Sm3+ and Dy 3+)
• Fluorapatite• Scheelite• Titanite
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Fluorapatite spectrum showing REE activation
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Titanite spectrum showing REE activation
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Scheelite (China) spectrum showing REE activation
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Gems with other activators
• Amber (organic)• Axinite• Cancrinite• Chalcedony (Uranium)• Opal (Uranium)• Petroleum and shell (organic)• Scapolite• Sodalite
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Amber (Arkansas) spectrum
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Opal (Hyalite) spectrum showing Uranium activation
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Sodalite spectrum
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Summary of Initial Research
• Diamond provenance, and activators need to be defined
• Other gem materials should be investigated for additional activators
• Potential for gem identification should be investigated