山东蓝宝石的主要致色因素

THE MAIN COLOR-CAUSING FACTORS OF SAPPHIRES IN SHANDONG PROVINCE

山东蓝宝石颜色深暗,与其主要致色元素有着直接关系。对其化学成分进行分析认为:Cr2O3是红色、橙黄色、黄色的主要致色因素。而w(TiO2)低,w(TFeO)高,尤其是Fe3+大于全铁的90%,TFeO/TiO2比值大是山东蓝宝石颜色深暗的主要原因。对其紫外-可见光-近红外吸收光谱进行分析,进一步得出Cr3+离子的d-d电子跃迁、成对Fe3+离子、单Fe3+离子的d-d电子跃迁、Fe2+-Ti4+之间的电荷转移、Fe2+-Fe3+之间的电荷转移等是山东蓝宝石致色的本质。代表绝大多数山东蓝宝石颜色的深蓝色蓝宝石,缺失紫外-可见光-近红外吸收光谱的575～711 nm吸收带,即缺少Fe2+-Ti4+之间的电荷转移。因此,针对性地选择w(TiO2)高的蓝宝石进行改善,或是设法加入TiO2、减少Fe3+含量、在还原条件下改变其TFeO/TiO2的比值,应是目前山东蓝宝石改色的关键。

The main color-causing elements are the major factors that make the dark color of sapphires in Shandong province. By the analysis of chemical compositions obtained from electron microprobe are as follows： Cr2O3 for red, orange and yellow; the low TiO2,high content of TFeO, especially Fe^3＋〉90% of TFeO, and big ratio of TFeO/TiO2, are the main factors that make the dark color of the sapphires. By the study of ultraviolet visible-near infrared absorption spectrum sketch, it is further concluded that Cr^3＋ d-d jump electron,Fe^3＋ coupling effect, Fe^3＋ d-d jump electron, charge transfer of Fe^2＋-Ti^4＋, and charge transfer of Fe^2＋-Fe^3＋ are the main factor for coloring of the sapphairs. The popular dark blue sapphires in Shandong province lack 575- 711nm absorption spectrum band of ultraviolet-visible-near infrared region,namely no Fe^2＋-Ti^4＋ charge transfer. Therefore, the most important for changing colors of the sapphires is to select sapphires with high TiO2 and lower the content of Fe^3＋, add TiO2 and reduce the ratio of TFeO/TiO2 under reductive condition.