彩色电气石致色离子的化学状态研究

Chemical States of Colour-induced Cations in Colourful Tourmaline

  • 摘要: 为探究不同颜色电气石中致色元素的化学状态及其化学环境, 利用X射线光电子能谱方法对绿色调(墨绿色、蓝绿色、淡绿色)和粉红色调电气石样品进行分析。结果表明, 绿色调和粉红色调电气石样品中均含有少量的过渡金属离子, 如Fe, Mn, Ti, Cr, 且不含Li和Be。不同颜色的电气石晶体中过渡金属阳离子的化学状态相同, 且分别为Fe3+, Mn4+, Ti4+, Cr3+, 但其与阴离子配位的环境有所差别。绿色调电气石样品中虽然Fe的质量分数有较大的差别, 但均有部分Fe元素与F结合, 即占据晶体结构中的Y位; 粉红色电气石样品中, Fe离子没有与F形成配位, 仅占据结构中的Z位。相反, 在粉红色电气石样品中, Mn主要与F结合配位的方式存在, 占据结构中的Y位, 而绿色调电气石样品中大部分的Mn与O配位成键, 只有少部分的Mn与F结合配位。由于Fe3+, Mn4+离子对之间电荷转移的可能性不大, 故电气石的颜色可能主要由于d—d电子跃迁和氧与金属离子(O2--M)间电荷转移吸收引起, 尤其是由于化学环境的差异(包括配位阴离子种类、杂质缺陷、结构畸变等)所引起。

     

    Abstract: X-ray photoelectron spectroscopy was used to investigate the chemical state and chemical environment of colour-induced metal cations in deep green,blue green,light green and pink tourmaline samples.The results show that both green and pink tourmaline samples contain Fe,Mn,Ti and Cr,but no Li and Be.Being Fe3+,Mn4+,Ti4+and Cr3+ respectively,the metal cations in different coloured tourmaline samples have the same chemical states. but they have different coordinated ions.Although varied Fe contents have been found in the green tourmaline samples,part of Fe coordinates with Fe occupying the Y position of the crystal structure。while no Fe has been found to coordinate with F in the pink tourmaline sample,all Fe in them occupying the Z position of the crystal structure,In the pink tourmaline sample Mn has been found to bond with Fe occupying the Y position,but in the green tourmaline sample most of the Mn bonds with 0 and only minor Mn coordinates with F.Fe and Mn in the tourmaline crystals are all in the state of Fe3+and Mn4+, and the charge transfer between the cation pairs is unlikely to take place.Thus the colour of tourmaline is probably induced due to the absorption of d-d ransition and charge transfer between oxygen and metal cations((O2--M),especially due to the different chemical environment,such as coordination with different ions,impurity, and structure distortion.

     

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