合成掺铁水晶同步辐射X射线吸收光谱初探

A Preliminary Synchrotron-Radiation XAS Study on Synthetic Iron Doped Coloured Quartz

紫晶等掺铁水晶的致色机理非常复杂,伴随着研究方法的进步对其致色机理认识逐渐深入。通过化学分析、紫外-可见光谱、电子顺磁共振、理论计算等研究方法,人们已经提出了多种致色模型。同步辐射X射线吸收光谱(XAS)技术,通过高亮度X射线激发样品中Fe离子的光电效应来采集吸收光谱,并对光谱中的边前峰、吸收边和主峰进行分析,可以直观了解Fe元素在掺铁水晶中的价态、占位情况。合成紫黄晶、绿水晶的颜色和Fe元素密切相关,利用XAS技术考察Fe元素在三者中的价态、占位情况有助于了解三种Fe致色水晶在致色机理上的差异。本文对水热法合成紫黄晶和绿水晶进行了同步辐射XAS实验,结果表明合成绿水晶中含有Fe^(2+)和Fe^(3+),并可能占据在八面体间隙(I6)。合成紫黄晶中以Fe^(3+)为主,紫晶区域Fe^(3+)占据对称型更低的四面体间隙或占据两种间隙位(I4和/或S)而黄晶区域中Fe^(3+)则只占据一种四面体位。实验结果证明了间隙位Fe^(3+)对紫晶致色具有重要意义,说明了Fe在不同颜色掺铁水晶中各不相同。

The colour mechanisms of Fe in iron doped quartz such as amethyst has bothered us for almost a century.Each times the research technology progresses,our understanding would go further.From chemical analysis,UV-Vis spectroscopy,EPR and theoretical calculation,scientists have established many colour mechanism models.Synchrotron-radiation Xray absorption spectroscopy can gathers the X-ray absorption spectra by high brilliant X-ray which can excite photoelectric effect from Fe ions in the samples.By analyzing pre-edge,absorption edge and edge crest(also known as white line)-the characteristics in XAS,we can tell the differences on valence states and occupations between synthetic amethyst,citrine and green quartz intuitively.This work focused on the preliminary XAS study on typical hydro-thermal synthetic ametrine and green quartz.The spectrum suggested that Fe in green quartz are Fe^(2+)mixed with Fe^(3+),and they are likely occupied in octahedral site(I6).The Fe in ametrine is Fe^(3+)mainly,but which in amethyst area may locate in interstitial site or both substitutional and interstitial sites(I4 or/and S)together,while in citrine area,Fe^(3+)prefer to locate in one kind of tetrahedral site.Our study supported previous colour mechanism works in some degree by XAS experiment.According to the gemological observation and XAS,we can say that Interstitial Fe^(3+)does relate to coloration profoundly,and there are some obvious differences from Fe in other iron doped colored quartz.