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

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 I_{6 840}/I_{6 820} is related to the alkali metal content what minus lithium contents.