俄罗斯祖母绿的紫外-可见光光谱、拉曼光谱、红外光谱特征

UV-Vis, Raman and Infrared Spectral Characteristics of Emerald from Russia

  • 摘要: 产自俄罗斯的祖母绿因其浓郁颜色和可观的产量成为国际彩色宝石市场不可缺少的部分,但目前关于俄罗斯祖母绿的谱学特征研究较少。本文利用激光剥蚀等离子质谱仪、紫外-可见分光光度计、拉曼光谱及红外光谱对俄罗斯祖母绿样品的成分、致色因素及结构特点进行测试研究。结果表明,俄罗斯祖母绿样品的化学成分中存在过渡金属离子Me(Fe、Mg、Cr等)替代Al,Al替代Si和Be,Li替代Be等多种类质同像替代共存的复杂情况。俄罗斯祖母绿样品的紫外-可见光谱均具有明显的Cr(+V)的谱,深浅不一的绿色样品主要由Cr3+致色,属于Ⅱ型祖母绿(高Cr低V型),因此浅色如薄荷绿色样品也可以称为祖母绿。俄罗斯祖母绿样品的拉曼光谱峰位相同,均显绿柱石谱,根据1 070 cm-1拉曼峰的半高宽值(FWHM)可确定俄罗斯祖母绿为片岩型。反射法测得其中红外指纹区(400~1 300 cm-1)中1 020 cm-1峰的分裂,与碱金属含量无明确相关性;透射法测得红外光谱结果显示4 000~8 000 cm-1区域主要是通道水的倍频与合频峰,位于5 107、5 279、5 438、6 820、7 075、7 140、7 275 cm-1,弱峰4 543、4 642、4 801、4 862 cm-1均属于Ⅰ型水,6 840、7 079 cm-1属于Ⅱ型水。I6 840/I6 820强度比与碱金属(不含Li)含量相关。

     

    Abstract: The emeralds from Russia, since their intense colour and considerable production, have an indispensable status in the international market. But there is few spectroscopy research on Russian emeralds. In the paper, the laser ablation plasma mass spectrometry (LA-ICP-MS), UV-Vis spectrophotometer, Raman spectroscopy and infrared spectroscopy were used to explore the chemical compositions, colour causes and structural characteristics of the Russian emerald. The results show that transition metal ions Me (Fe, Mg, Cr, etc.) substitute Al, and that Si and Be substitute Al, and that Li substitutes Be and other complicated isomorphism substitutions. UV-Vis spectra show distinct Cr (+v) absorption bands, and the green colour is mainly caused by Cr3+ ions, so emeralds from Russia belong to type Ⅱ emerald (high Cr low v type), and mint green samples, whose colour is very light, could also be called emerald. Raman spectroscopy determine all samples are beryl. According to the full width at half maximum (FWHM) of the 1 070 cm-1 Raman shift, the emerald from Russia is schist type. The band positions in the mid-infrared fingerprint area (400-1 300 cm-1), measured by reflection method, don't indicate the correlation between the band positions and the alkali metal contents. The infrared spectra measured by transmission method show that the overtones and combinations frequency vibration of channel water are in 4 000-8 000 cm-1 regions. The bands of 5 107, 5 279, 5 438, 6 820, 7 075, 7 140, 7 275 cm-1, including weak bands in 4 543, 4 642, 4 801, 4 862 cm-1, could attributed to type Ⅰ water and the bands of 6 840, 7 079 cm-1 belong to type Ⅱ water. The intensity ratio of I6 840/I6 820 is related to the alkali metal content what minus lithium contents.

     

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