绿柱石中铁离子的晶格占位及致色作用

绿柱石族宝石颜色丰富,一直是市场上重要的宝石品种。几十年来,国内外学者对不同颜色绿柱石的致色机理及改色工艺开展了广泛的研究。铁离子作为重要的致色过渡金属离子之一,其价态调控是绿柱石改色工艺的关键,所以铁离子的价态、晶格占位和对应的致色作用也一直是绿柱石研究的焦点。铁离子被认为可能存在于绿柱石中的铝氧八面体Al³⁺格位、硅氧四面体Si⁴⁺格位、铍氧四面体Be²⁺格位、结构通道2a或2b位和晶格间隙6g位等位置,是蓝、绿或黄等颜色绿柱石的主要致色元素。本文通过对绿柱石的晶体结构、铁离子的核外电子排布和晶格占位等方面文献资料的梳理及综合分析,认为Fe²⁺和Fe³⁺分别对蓝色和黄色绿柱石的呈色起着主导作用。当Fe²⁺和Fe³⁺处于晶格中不同位置时致色作用的具体差异,仍有待于进一步研究。

Site occupancy and coloring mechanisms of iron ions in beryl

The beryl family is known for its wide range of colors and has always been an important gemstone variety in the market. Over the past few decades, scholars both domestically and abroad have conducted extensive research on the coloration mechanism and color-modification techniques of beryls of different colors. As one of the important coloration transition-metal ions, the valence state regulation of iron ion is critical in the color-modification process of beryls. Therefore, the valence state, site occupancy, and corresponding chromogenic effects of iron ions have always been the focus of beryl research. Iron ions are believed to exist in various sites within the beryl crystal structure, including the aluminum octahedral Al³⁺ site, silicon tetrahedral Si⁴⁺ site, beryllium tetrahedral Be²⁺ site, structural channel 2a or 2b site, and lattice interstitial site 6g, and are the main color-causing elements for blue, green, or yellow beryls. Through a review and comprehensive analysis of the literature on the crystal structure of beryl, site occupancy and the arrangement of outer electrons of iron ions, we suggest that Fe²⁺ and Fe³⁺ play a dominant role in the coloration of blue and yellow beryls, respectively. Further research is needed to determine the specific differences in color-causing effects when Fe²⁺ and Fe³⁺ are located in different sites within the lattice.