高温热处理橙色蓝宝石的赋色机制

Colouring Mechanism of High-Temperature Heat-Treated Orange Sapphire in Madagascar

马达加斯加橙色蓝宝石的颜色究竟是扩散处理致色 ,还是高温热处理或辐照处理赋色 ?就此争议问题 ,采用 ICP-MS、 EPMA、 ESR、 UV等分析测试方法 ,对这种橙色蓝宝石进行综合对比研究。结果表明 ,橙色蓝宝石的化学成分以相对富 Cr、贫 Fe和 Ti为特征 ,自外向内过渡金属离子化学配比相对均匀 ,少数样品表层中 Be的丰度存在局部富集现象。由 Fe-O-杂质离子心的作用导致吸收谱带位移至可见光蓝紫区 (4 5 4nm) ,并叠加在由 Cr3 +离子的 4A2 (4F)→ 4T1(4F)自旋允许跃迁致吸收谱带之上 ,它与 Cr3 +离子联合吸收后的残余能量组合成橙色蓝宝石的色调。初步证实 ,外来的 Be2 + 不属致色离子 ,它不直接参与蓝宝石呈色 ,而是起到一种类似活化剂或拓展空位的作用 ;高温、增氧及 Be活化剂是导致橙色蓝宝石显橙黄色的主要外因条件 ;Fe— O-杂质离子心、Cr3 +和 Fe3 +离子是橙色蓝宝石致色的主要内因条件。推测高温热处理的温度与时间间隔、替位杂质 (Fe,Cr,Ti)离子的价态与浓度及晶格缺陷密度共同制约了橙黄色色层的厚度。

The controversial question whether the colour of Madagascar orange sapphire is caused by the diffusion treatment, by the high temperature treatment, or by the irradiation colouring can be answered by the application of such testing methods as ICP MS, EPMA, ESR, UV and the comprehensive correlation research on this type of orange sapphire. As shown in the research results, the chemical composition of the orange sapphire is relatively rich in Cr and poor in Fe, Ti, the chemical mixture ratios of the transitional metal ions are relatively homogenous from the exterior to the interior, and the abundance of Be is locally concentrated on the surface of a few samples. The Fe-O - impure ion center makes the absorption band move to the blue violet (454 nm), which superimposes on the absorption band resultled from the Cr 3+ [ 4A 2( 4F)→ 4T 1( 4F)]ion spins, and then combines with the residual energy from the Cr 3+ ion absorption into the hue of the orange sapphire. The initial investigation proves that the foreign Be 2+ is not included in the colouring ions. It is not related to the colouring of the sapphire, and serves as a kind of activator or channel diffusion. The major external conditions for the orange yellow colouring are the high temperature, increase in oxygen and Be activator, while the major internal conditions are Fe-O - impure ion center, Cr 3+ and Fe 3+ ions. Furthermore, the thickness of the orange yellow layer is constrained by the temperature and time interval of the high temperature heat treatment, and the valence state and concentration of the replacing impure ions (Fe, Cr, Ti) and the density of the defect in the crystal lattice.