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首先,对61个天然翡翠样品进行检测,其中22个天然翡翠荧光背景不明显,可以直接通过普通喇曼光谱识别部分翡翠特征峰,另外39个样品具有明显的荧光干扰信号。图 1所示是天然翡翠5号样品的喇曼检测谱图。通过普通喇曼光谱检测可直接识别310cm-1,378cm-1,521cm-1,698cm-1,1037cm-1的特征峰。而差分喇曼光谱将干扰较多的波段进行弱信号复原后,除了可以识别上述喇曼特征外,还可在434cm-1,581cm-1,988cm-1识别到更多的喇曼特征。其中,4条谱带都与具共价键链性质的氧四面体链有关,378cm-1属Si—O—Si键的不对称弯曲振动。而喇曼信号较弱的谱带310cm-1,434cm-1,521cm-1,581cm-1则属于离子键性质的M—O伸缩振动及其与Si—O—Si弯曲振动的耦合振动。1037cm-1和988cm-1可归属于Si—O键对称伸缩振动,698cm-1属Si—O—Si键的对称弯曲振动[15]。
天然翡翠样品中部分样品呈鲜绿色,翡翠中的鲜绿色一般是由于存在铬离子所致[16]。检测中光谱仪中光子照射到翡翠表面时,翡翠中铬离子会吸收大量光子用于外层电子跃迁,而位于高能级的电子不稳定,会返回到低能级,在返回过程中会产生大量荧光。此荧光光子与喇曼信号均会被喇曼光谱仪所接收,因此喇曼光谱的谱图上会出现非常强的荧光包络[17],干扰样品的正常识别。如图 2所示,4号天然翡翠就是因为样品的荧光干扰极其强烈,荧光谱峰掩盖了大部分散射喇曼特征峰,通过原始谱图很难获得有用的喇曼信号。而采用差分喇曼光谱仪进行检测时,基于Kasha’s rule,分子发射的荧光或磷光只能从某一多重态中的最低态激发,因此激发光源的微小频移并不改变荧光信号,而喇曼散射光谱其散射波长仅与激发光和物质官能团相关,针对这一差异设计的滤波系统可以将特定差分特征信号从原始噪声中有效地提取出来[18]。如图 2所示,差分喇曼光谱谱图峰形尖锐清晰,干扰信息少,可以准确地从高荧光低信噪比的原始信号中获得翡翠的喇曼特征378cm-1,434cm-1,521cm-1,581cm-1,698cm-1,1037cm-1。
很多学者[19-20]提及荧光小的翡翠一般属于A货翡翠,荧光高的翡翠很可能为B货翡翠。而经过实验证明,结果与其结论并不完全一致。翡翠属于多矿物集合体,成分复杂,含有各种伴生矿物及及致色离子,而这些物质均有可能产生荧光背景。天然翡翠中,有些翡翠几乎没有荧光背景,而有些翡翠又具有很高的荧光背景。同一个样品,不同检测点位检测的喇曼光谱谱图信号强弱及特征峰也不尽相同,一般情况下,绿色面的荧光背景一般均高于浅色部位。在实际检测中,天然翡翠的喇曼特征中也有不归属于翡翠的特征峰,可能是归属于其它伴生矿物成分。因此,荧光背景高只能说明样品中含有高荧光物质,翡翠是个复杂的物质,不能单以荧光背景强弱来鉴定是否为天然翡翠。
通过差分喇曼光谱仪滤除荧光,不同翡翠检测的喇曼特征峰并不完全一致。但61个天然翡翠样品都可检测到翡翠的主要特征峰378cm-1,698cm-1,1037cm-1,这3个喇曼位移的特征峰峰形较为尖锐,容易辨认且强度较强,是翡翠硬玉结构的特征喇曼位移,可与其它相似宝玉石进行区分,进行种属鉴别。
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由上述实验可知,差分喇曼光谱相对于普通喇曼光谱可滤除样品荧光,进行弱信号还原,可获得更多及更清晰的喇曼特征,因此,本实验中采用差分喇曼光谱仪对翡翠进行鉴别。首先,对市场上两种常见的注胶材料进行检测,结果如图 3所示。两种注胶材料有很多相同的喇曼特征峰,345cm-1,394cm-1,563cm-1,636cm-1,816cm-1,1004cm-1,1114cm-1,1188cm-1,1227cm-1,1299cm-1,1466cm-1,1611cm-1。这是因为市面上注胶材料多为环氧树脂,虽然环氧树脂有很多型号,但是它们都属于芳烃类,是含苯的碳氢化合物,结构相似。尤其是1611cm-1和1116cm-1这两个谱带,不仅相对强度更强,峰形也最为尖锐特征。因此,如果一件翡翠制品的喇曼光谱,除了硬玉或者其它共生矿物的特征谱带之外,发现有这些特征峰的存在,可结合结合翡翠其它特征信息,判定翡翠是否为B货[11]。
由于胶被充填在翡翠的酸洗裂缝中,难以通过喇曼光谱仪直接识别。但通过联用显微附件,可以清楚地寻找到翡翠裂纹,精细调节焦距,使焦点对准凹坑处进行检测,分辨其是否含有环氧树脂的喇曼特征,以此来鉴定翡翠是否经过注胶充填。图 4为注胶翡翠的显微放大图及其裂纹处的喇曼光谱图。如图 4可见,翡翠表面有凹坑及填充痕迹,通过普通的放大镜很难发现,使用显微镜则可以很明显发现此处凹坑。
联用差分喇曼光谱,将焦点对准此处凹坑,检测结果如图 5所示。呈现的喇曼特征中310cm-1,378cm-1,433cm-1,521cm-1,698cm-1,1037cm-1与表征天然翡翠的喇曼特征峰相同,说明其主要成分相同。而其中又多产生了1114cm-1,1188cm-1及1611cm-1的喇曼特征峰。其中,1611cm-1和1116cm-1属苯基中具共价键性质的碳碳伸缩振动, 1189cm-1属苯环的碳氢面内弯曲振动。这些特征峰同注胶材料树脂的部分特征峰一致,可以判定此翡翠经过了有机物填充,且有可能为环氧树脂。
用同样方法对剩余50个注胶翡翠进行检测,均可以识别翡翠的3个主要特征峰378cm-1,698cm-1,1037cm-1。同时也会识别到注胶材料的部分特征峰,51个注胶翡翠中注胶材料的特征峰识别情况如表 1所示。其中1114cm-1,1188cm-1,1611cm-1识别频次较多,特别是归属于苯基中具共价键性质的碳碳伸缩振动1114cm-1的喇曼特征峰在所有注胶翡翠中均能被识别,说明其中均经过有机物填充。通过差分喇曼光谱联用显微镜识别注胶材料特征峰1114cm-1,1188cm-1,1611cm-1可以对A、B货翡翠进行快速无损的鉴定。
Table 1. Frequency of characteristic peaks of glue-injected material in B jadeite rubber injection jadeite
characteristic peaks of glue injection materials/cm-1 345 394 563 636 816 1004 1114 1188 1227 1299 1466 1611 frequency/times 3 4 7 0 10 5 51 42 14 9 15 48
便携式差分喇曼光谱技术在翡翠鉴定中的研究
Study on shifted-excitation Raman difference spectroscopy in the identification of jade
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摘要: 为了实现对翡翠种属及注胶翡翠的鉴定,采用显微联用位移激发差分喇曼光谱法进行了理论分析与实验验证,得到了112个翡翠样品的差分喇曼光谱数据,比较了翡翠的差分喇曼光谱和普通喇曼光谱,并统计分析了翡翠的喇曼特征峰及B货翡翠的鉴别依据。结果表明,差分喇曼可有效滤除荧光,对识别高荧光翡翠样品的特征峰有显著优势;378cm-1,698cm-1,1037cm-1峰强较强、峰形尖锐,是检测翡翠时出现频率最高特征峰,可以借此对样品种属进行鉴定;通过显微放大能观察到B货翡翠经酸洗产生的裂纹、凹坑及其充填的有机物,并在此处可检测到有机物的喇曼特征峰,其中1114cm-1,1188cm-1,1611cm-1出现最为频繁,可以此对翡翠的A货、B货进行鉴定。该方法操作简单、提高鉴定效率,可为翡翠的快速鉴定提供参考。
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关键词:
- 光谱学 /
- 鉴别 /
- 位移激发差分喇曼光谱 /
- 翡翠
Abstract: In order to realize the identification of jadeite species and rubber-injected jadeite, theoretical analysis and experimental verification were carried out by using microscope combined with shifted-excitation Raman difference spectroscopy(SERDS), and SERDS data of 112 jadeite samples were obtained. The SERDS and ordinary Raman spectrum of jade were compared, and the Raman characteristic peaks of jade and the identification basis of B jade were statistically analyzed. The results show that the SERDS can effectively filter out the fluorescence and has a significant advantage in identifying the characteristic peaks of high-fluorescence jadeite samples. The peaks at 378cm-1, 698cm-1, and 1037cm-1 are relatively strong and have sharp peak shapes. They are the characteristic peaks with the highest frequency when detecting jadeite, which can be used to identify sample species. The cracks, pits and the organic matter filled by the pickling of the B jadeite can be observed by microscopic magnification. The Raman characteristic peaks of the organic matter can be detected here, of which 1114cm-1, 1188cm-1, 1611cm-1 appear most frequently, jade goods A and B can be identified through this method is simple to operate and the identification efficiency can be improved. This method can provide a reference for the rapid identification of jadeite.-
Key words:
- spectroscopy /
- identify /
- shifted-excitation Raman difference spectroscopy /
- jade
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Table 1. Frequency of characteristic peaks of glue-injected material in B jadeite rubber injection jadeite
characteristic peaks of glue injection materials/cm-1 345 394 563 636 816 1004 1114 1188 1227 1299 1466 1611 frequency/times 3 4 7 0 10 5 51 42 14 9 15 48 -
[1] JIANG T L, LI K. Research progress of jadeite[J]. Shandong Chemical Industry, 2019, 48(12): 65-65(in Chinese). [2] HUANG X. Optimization and identification characteristics of jadeite[J]. China Gemstone, 2011, 28(4): 168-169(in Chinese). [3] PANG T T, DENG F, LIN J F. Introduction and idetification of optimizing processed jadeite and jade imitation[J]. Superhard Materials Engineering, 2015, 27(4): 53-57(in Chinese). [4] CHEN M Z. Rapid and non-destructive identification of jadeite using Raman spectroscopy[J]. Spectroscopy Laboratory, 2013, 30(3): 1234-1237(in Chinese). [5] XING Y Y, HE Y. A preliminary study on the spectral characteristics of jadeite synthesized at high temperature and high pressure[J]. Journal of High Pressure Physics, 2018, 32(6): 11-18(in Chinese). [6] LIU F L, NIE SH F, LIU F, et al. Identification features of peicui's new process "paste color"[J]. Journal of Gems and Gemology, 2016, 18(A1): 54-57(in Chinese). [7] GU L F, WANG Z H, ZHANG Y, et al. Research on pattern recognition of jadeite based on Raman spectrum[J]. Analysis Laboratory, 2013, 32(12): 22-26(in Chinese). [8] LIU H K, CHEN P Y, KU Y M. The spectral characteristics and coloring mechanism of jadeite[J]. Guangdong Chemical Industry, 2013, 40(16): 247-248(in Chinese). [9] XUE L, WANG Y Q, FAN J L. Application of raman spectroscopy in nondestructive identification of jade[J]. Journal of East China University of Science and Technology (Natural Science Edition), 2009, 35(6): 857-859(in Chinese). [10] FAN J L, GUO Sh G, LIU X L. Application ofmicro-Raman technology in emerald detection[J]. Applied Laser, 2007, 27(1): 21-24(in Chinese). [11] SHREVE A P, CHEREPY N J, MATHIES R A. Effective rejection of fluorescence interference in Raman spectroscopy using a shifted excitation difference technique[J]. Applied Spectroscopy, 1992, 46(4): 707-711. doi: 10.1366/0003702924125122 [12] MATOUSEK P, TOWRIE M, PARKER A W. Simple reconstruction algorithm for shifted excitation Raman difference spectroscopy[J]. Applied Spectroscopy, 2005, 59(6): 848-851. doi: 10.1366/0003702054280757 [13] SHI Y J, ZHANG F, LI H J, et al. Analysis on jadeite processing technology[J]. Resource Investigation and Environment, 2013, 34(2): 72-74. [14] CHEN Y L, WANG X, YIN X. Identification characteristics of jadeite[J]. Geology and Resources, 2007, 16(2): 143-144(in Chinese). [15] ZU E D, CHEN D P, ZHANG P X. Raman spectroscopic identification of jade B cargo[J]. Spectroscopy and Spectral Analysis, 2003, 23(1): 64-66(in Chinese). [16] WANG H B, CONG P Sh, ZHU Zh L. Raman spectroscopy fluorescence background study of natural and processed jadeite[J]. Guangdong Chemical Industry, 2013, 40(10): 1-2(in Chinese). [17] FANG J L, GUO Sh G, LIU X L, et al. Spectroscopic research on natural and processed jadeite[J]. Laser and Infrared, 2007, 37(8): 769-772(in Chinese). [18] da SILVA MARTINS M A, RIBEIRO D G, dos SANTOS E A P, et al. Shifted-excitation Raman difference spectroscopy for in vitro and in vivo biological samples analysis[J]. Biomedical Optics Express, 2010, 1(2): 617-626. doi: 10.1364/BOE.1.000617 [19] ZHAO X U, ZHU Y. Synergetic degradation of rhodamine B at a porous ZnWO4 film electrode by combined electro-oxidation and photocatalysis[J]. Environmental Science & Technology, 2006, 40(10): 3367-3372. [20] ZHANG Q F, TAMMY P, CHOU B R, et al. Aggregation of ZnO nanocrystallites for high conversion efficiency in dye-sensitized solar cells[J]. Angewandte Chemie International Edition, 2008, 47(13): 2436-2440.