宝石分析和身份验证

There are technical tools to help thwart the counterfeiters. Raman spectroscopy and related techniques are effective for quickly and easily discriminating many natural from artificial stones, nondestructively and with no sample preparation.

Background

Among the most commonly counterfeited and substituted gems are stones such as diamonds, emerald, ruby and jade, and substances such as amber, coral and pearl. Yet all have unique spectral characteristics that can be identified with powerful spectral instrumentation and proven methodologies.

For example, Raman spectroscopy can explore the molecular structure of the gemstone. The spectral fingerprints provided by Raman spectroscopy contain peaks that can be tied to a gemstone’s chemical structure, as well as the trace minerals and inclusions that give stones such as emerald and ruby their distinctive hues (Figure 1).

Figure 1: Raman spectroscopy is an excellent tool for gemstone analysis. In this graph, the intensity has been shifted to facilitate comparison of spectral shape differences.

Luminescence induced by a high-power, short-wavelength light source offers additional information that can be used to authenticate and to detect various gemstone treatments. Natural and synthetic emeralds, for example, have the same chemical structure and therefore identical Raman spectra. Both get their deep green color from the presence of chromium and vanadium ion impurities, but slight differences in the concentrations and presence of other metal impurities affect the intensity and wavelength of the chromium photoluminescence bands, allowing synthetic emeralds to be distinguished from natural types.

还有更多。使用532 nm激发激光同时进行的拉曼和光致发光测量可以使宝石学家能够确定是否已经染色了珊瑚和淡水珍珠以增强其自然色，从而人为地提高其价值。

Authenticating Natural Diamonds

Synthetically grown and artificially treated diamonds often are sold as natural diamonds, with improved fabrication and processing methods making authentication more difficult. A system developed by an Ocean Insight solutions partner¹and powered by one of ourhigh-sensitivity Raman spectrometersis capable of measuring both Raman signal and photoluminescence concurrently, providing comprehensive analysis of natural diamonds and their simulants. Here are two examples:

• Natural diamond has a strong Raman peak at 1332 cm^-1, while diamonds produced using chemical vapor deposition (CVD) processes have no such peak -- a feature that allows near-instant authentication.
  
  
• Less desirable brown and gray diamonds are annealed to near-colorless using high-pressure, high-temperature (HPHT) treatments. Though HPHT-treated diamonds cost up to 65% less than authentic diamonds and may be sold as natural stones, they lack several photoluminescence peaks typically seen in the Raman/photoluminescence spectrum of natural diamonds (Figure 2).

Figure 2: Naturally clear diamonds exhibit photoluminescence peaks from 530-600 nm. HPHT treatment removes most of these peaks, leaving only nitrogen-vacancy peaks at 576 nm and 637 nm in some samples.

Zircon is another natural gemstone that can be heated to make it colorless and more closely resemble diamond. (Zircon should not be confused with cubic zirconia, an inexpensive synthetic gemstone that’s very popular as a diamond simulant.) Raman analysis of zircon and diamond can be applied to reveal different spectral characteristics for each (Figure 3).

Figure 3: Distinct spectral differences can be observed in comparing diamond and zircon samples.

Identifying Amber Specimens

尽管在世界上几个地区发现了琥珀，但以其发现的墨西哥地区命名的Chiapas Amber因其透明度和令人惊叹的颜色而闻名，从蜂蜜到绿色，蓝色，蓝色，紫罗兰色和深红色。恰帕斯琥珀比波罗的海和其他地区的琥珀更难，是珠宝和雕刻的理想选择。这种化石树脂需要数百万年的形成，但有时会使用人造树脂和眼镜模仿。

In a 2014 paper, investigators at the Centro de Investigaciones en Óptica, A. C. in León, Mexico compared false amber to specimens from the Baltic and Chiapas regions, observing fluorescence excited with a tunable Argon-ion laser at 457 nm, 488 nm, 514 nm and multi-line outputs².

The fluorescence was detected with an Ocean InsightUSB4000 spectrometerfor the Baltic and Chiapas amber superimposed with the scattered laser light, but no fluorescence was seen for the false amber (Figure 4). Even comparing fluorescence spectra for the true amber, a slight shift in the emission peak could be seen for the Chiapas amber at ~525 nm as compared with the Baltic amber at ~535 nm. The researchers found that Raman spectroscopy also distinguished false from true amber, and more clearly identified amber from different regions.

Figure 4: Unlike naturally occurring amber, false amber has no fluorescence response. Additional investigation also reveals differences in Chiapas and Baltic amber samples.

Determining the Color of Pearls

培养的淡水珍珠从称为多烯的有机色素中获得自然色，这些珍珠表现出增强的拉曼散射。染料可用于生产彩色珍珠来模拟稀有天然标本，从而使视觉识别非常具有挑战性。

Spectroscopy, however, tells a different story.

其自然状态的培养淡水珍珠具有宽阔的，始终如一的发光峰，由可归因于aragonite（一种碳酸钙）和多烯化合物的拉曼峰点点峰（图5）。染色培养的淡水珍珠与明显的对比度可以表现出由于染色剂而表现出多种发光曲线（图6）。虽然可能无法鉴定染色剂，但是光致发光的拉曼光谱使鉴定染料的不存在或存在变得非常容易，从而验证了培养的淡水珍珠的价值。

Figure 5: Natural freshwater pearls have characteristic Raman peaks associated with aragonite, a carbonate mineral.

Figure 6: Dyed pearls produce various luminescence curves.

Identifying Dyed Corals

Coral comes in a variety of shades, from light pink to deep red. While coral can be positively identified by looking under a microscope for the characteristic grooves used to transport nutrients, the traditional test for dyed coral requires swabbing the specimen with acetone, risking damage to the sample.

Naturally colored coral has distinctive Raman peaks on a characteristic photoluminescence background. These peaks indicate forms of calcium carbonate, as well as the polyacetylenes and carotenoids that imbue coral with such beautiful color. When dyed coral is subjected to the same measurement, a much broader photoluminescence curve is seen (Figure 7). This curve is centered at a different wavelength and lacks Raman peaks.

图7：与与天然珊瑚相关的更明显的拉曼峰相比，染色的珊瑚曲线表现出广泛的发光曲线。

Identifying dyed corals from natural may seem like an esoteric pursuit, until one realizes that some dyed corals are protected species that have been harvested illegally and fraudulently marketed as permitted for legal trade.

Classifying Emeralds

Emerald owes its stunning deep green color to the presence of chromium (Cr³⁺) and vanadium (V³⁺) ions in a beryl crystal matrix. Both natural and synthetic emeralds have the same chemical structure, making it difficult to discriminate the two. While emeralds exhibit no distinctive Raman peaks, they do show two Cr³⁺photoluminescence bands, the exact positions of which are influenced by the presence of other impurities like magnesium, titanium and zinc in the beryl structure. This allows synthetic emerald to be distinguished from the two natural types of emerald, schist and non-schist (Figure 8).

Figure 8: Subtle differences between authentic and synthetic emeralds are revealed in spectral analysis.

Synthetic emerald also tends to have higher chromium ion concentrations than natural emerald, which results in stronger photoluminescence peaks. Even when a natural emerald owes its color primarily to vanadium ions, the chromium ion concentration is still high enough to exhibit photoluminescence, making this a very effective method to authenticate natural emeralds.

Applying Spectroscopy Techniques to Other Gemstones

那些负责识别和认证宝石的人需要基于声学科学的强大设备。紧凑的光谱系统在许多层面上都很好地填充了该角色，因为可以轻松优化仪器以检测与天然宝石相关的光谱峰和模式（图9），合成学和其他假冒物。

Figure 9: The word "jade" describes the minerals jadeite or nephrite. Raman spectroscopy helps to reveals differences in jade types and point of original.

光谱学的力量超过了我们所有的感官,for it analyzes the very nature of materials.

亚博最新网站多少无论是在实验室还是在现场中，海洋洞察模块学光谱系统都提供了许多来应对欺诈的方法，并将仪器配置为用于研究的单个设置或集成到另一个设备中的自定义解决方案。

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