摘要
坦桑尼亚Umba出产颜色丰富的刚玉,该研究对象是一颗来自Umba的具有特殊变色效应的蓝宝石,D65光源(色温6500K)下呈现淡黄色,A光源(色温2856K)下呈现淡紫红色。为了研究这颗变色蓝宝石紫外-可见光光谱中的谱峰归属与变色成因,该研究使用电荷补偿理论来分析此样品紫外-可见光光谱中的谱峰归属。采用紫外-可见分光光度计(UV-Vis)和激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)对这颗变色蓝宝石进行了测试。结果发现,变色蓝宝石紫外-可见光光谱中存在位于377,388和450nm处的3个吸收峰和1个以560nm为中心的宽缓吸收带。样品的颜色主要受450nm处吸收峰和以560nm为中心的吸收带影响,其中以560nm为中心的吸收带造成了这颗蓝宝石的变色效应。根据激光剥蚀电感耦合等离子体质谱仪的测试结果,样品中主要杂质元素有Fe,Ti,Cr,V和Mg等。样品紫外-可见光光谱中377,388和450nm处的吸收峰是由Fe^3+导致。蓝宝石中的Cr^3+,V^3+,Fe^2+-Ti^4+对都可以在560nm附近产生吸收,结合电荷补偿理论分析,刚玉中的Mg^2+会优先和Ti^4+进行电荷补偿,样品中Mg含量要稍微高于Ti,推测样品中几乎所有Ti^4+会与Mg^2+进行电荷补偿,因此样品中几乎不会存在Fe^2+-Ti^4+对。Fe^2+-Ti^4+对电荷转移产生的吸收特征具有很强的偏振性,尤其是在580nm以后的吸收特征会随着偏振方向的改变而有很明显的变化。偏振紫外-可见光光谱测试发现以560nm为中心的吸收带没有明显的偏振性,进一步验证了样品中几乎没有Fe^2+-Ti^4+对,因此以560nm为中心的吸收带主要是由于Cr^3+和V^3+造成的。样品的颜色主要是由Fe^3+,Cr^3+和V^3+引起的,而变色效应主要是由Cr^3+和V^3+导致。结合电荷补偿机制与偏振-紫外可见光光谱来解释这颗变色蓝宝石的紫外-可见光光谱中以560nm为中心的吸收带的归属,为研究刚玉紫外-可见光光谱中较为常见的位于560nm左右吸收带的归属提供了一种新的研究思路。
Many colorful corundum crystals were found in Umba,Tanzania.The sample of this study is a sapphire with special color-changed effect from Umba.It shows slight yellow under D65 light source (colour temperature is 6 500 K) and slight purplish red under A light source (colour temperature is 2 856 K).In order to study the UV-Vis spectroscopy and the origin of the color-changed effect of this sapphire,the charge compensation theory was innovatively used to analyze the assignment of absorption characteristic in UV-Vis spectrum.UV-Vis spectrophotometer and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) were used to test the sample.The result showed that there are three absorption peaks at 377,388 and 450 nm and a absorption band centered at 560 nm in UV-Vis spectrum of the sample.The color of the sample is mainly affected by the peak at 450 nm and the band centered at 560 nm,which leads to the color-changed effect.According to the results of LA-ICP-MS,the trace elements in this sample are Fe,Ti,Cr,V,Mg,etc.The absorption peaks at 377,388 and 450 nm in the UV-Vis spectrum of samples are caused by Fe^3+.The absorption features near 560 nm may be caused by Cr^3+,V^3+,Fe^2+-Ti^4+ pairs in sapphire.Combining with charge compensation theory,Mg^2+ will preferentially compensate with Ti^4+ in corundum.The content of Mg in sample is slightly higher than that of Ti.So almost all Ti^4+ will compensate with Mg^2+ and almost no Fe^2+-Ti^4+ pair exists in the sample.The absorption characteristic of charge transfers between Fe^2+ and Ti^4+ has strong polarization.The absorption characteristic caused by Fe^2+-Ti^4+ pairs,especially after 580 nm,will change obviously with the change of polarization direction.Polarized UV-Vis Spectrum of this sapphire shows that there is no obvious polarization feature on the absorption band centered at 560 nm,which could further confirm that there is almost no Fe^2+-Ti^4+ pair in the sample.Thus the absorption band centered at 560 nm is mainly caused by Cr^3+ and V^3+.The color of sample is mainly caused by Fe^3+,Cr^3+,V^3+ and the color-changed effect is mainly caused by Cr^3+ and V^3+.This research innovatively combines charge compensation mechanism and polarized UV-Vis spectroscopy to explain the assignment of the absorption band centered at 560 nm in the UV-Vis spectrum of this color-changed sapphire.It provides a new method to study the assignment of the absorption band around 560 nm which is a common absorption characteristic in UV-Vis spectrum of corundum.
作者
陈超洋
黄伟志
邵天
沈澈
李志彬
沈锡田
CHEN Chao-yang;HUANG Wei-zhi;SHAO Tian;SHEN Che;LI Zhi-bin;Andy Hsitien Shen(Gemmological Institute,China University of Geoscience (Wuhan),Wuhan 430074,China;School of Civil and Resource Engineering,University of Science and Technology Beijing,Beijing 100083,China)
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2019年第8期2470-2473,共4页
Spectroscopy and Spectral Analysis
基金
国家重点研发计划(2018YFF0215403)资助
关键词
蓝宝石
变色效应
紫外-可见光光谱
谱峰归属
Sapphire
Color-changed effect
UV-Vis spectrum
Assignments of spectral characteristics
