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Lu R.,GIAs New York Laboratory
Gems and Gemology | Year: 2012

The market value of jadeite has risen dramatically in recent decades, often rivaling that of fine ruby and sapphire. Understanding the color origin of jadeite and reliably determining treatments have become increasingly important in the trade. This study uses single-crystalline analogs in conjunction with polycrystalline jadeite to examine the color origin of lavender jadeite through quantitative spectroscopy and modern trace-element analytical techniques. Several previously proposed chromophores are assessed for their possible contribution to jadeite coloration. Quantitative analysis confirms that green and lavender colorations are caused by chromium and manganese, respectively. The relative significance of these two chromophores is compared to determine their impact on observable coloration. The findings on color origin are applied to the identification of treated material on the current market. © 2012 Gemological Institute of America. Source

Wang W.,GIAs New York Laboratory | D'Haenens-Johansson U.F.S.,GIAs New York Laboratory | Johnson P.,GIAs New York Laboratory | Moe K.S.,GIAs New York Laboratory | And 3 more authors.
Gems and Gemology | Year: 2012

Gemological and spectroscopic properties of CVD synthetic diamonds from Gemesis Corp. were examined. Their color (colorless, near-colorless, and faint, ranging from F to L) and clarity (typically VVS) grades were comparable to those of top natural diamonds, and their average weight was nearly 0.5 ct. Absorption spectra in the mid- and near-infrared regions were free from defect-related features, except for very weak absorption attributed to isolated nitrogen, but all samples were classified as type IIa. Varying intensities of [Si-V] - and isolated nitrogen were detected with UV-Vis-NIR absorption spectroscopy. Electron paramagnetic resonance was used to quantify the neutral single substitutional nitrogen content. Photoluminescence spectra were dominated by N-V centers, [Si-V]-, H3, and many unassigned weak emissions. The combination of optical centers strongly suggests that post-growth treatments were applied to improve color and transparency. PL spectroscopy at low temperature and UV fluorescence imaging are critical in separating these synthetic products from their natural counterparts. © 2012 Gemological Institute of America. Source

D'Haenens-Johansson U.F.S.,GIAs New York Laboratory | Moe K.S.,GIAs New York Laboratory | Johnson P.,GIAs New York Laboratory | Wong S.Y.,GIAs Hong Kong Laboratory | And 2 more authors.
Gems and Gemology | Year: 2014

The gemological and spectroscopic properties of 52 colorless to fancy light-colored HPHT synthetic diamonds (40 of them colorless or near-colorless) produced by AOTC using either toroid- or BARS-press technologies were characterized. In addition to achieving excellent color grades, these commercially available faceted synthetics had a weight range of 0.05 to 0.80 ct, and possessed IF to I2 clarity. Their synthetic origin may be difficult to determine with standard gemological techniques alone, but they were conclusively identified using advanced testing methods, including photoluminescence, FTIR spectroscopy, and fluorescence imaging. Inclusions in two samples, grown by different press types, were studied using LA-ICP-MS. The trace-elemental analysis results indicated that the inclusions formed by the trapping of the solvent/catalyst melt during synthesis. Analysis of the combined multi-technique data provided insight into the identities of the solvents, catalysts, and nitrogen getters possibly used to grow high-quality HPHT synthetic diamonds. © 2014 Gemological Institute of America. Source

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