金绿宝石和变石的呈色机理

Mechanism of Chrysoberyl and Alexandrite Color

对24块世界主要产地的金绿宝石和变石进行X荧光能谱分析,得到其所含的主要微量元素分别是Fe、Ga、Ti和Fe、Cr、Ti.金绿宝石和变石各1块样品的同步辐射X荧光能谱半定量分析表明金绿宝石中Fe含量平均为17 800×10-6,Cr为855×10-6;变石中Fe含量为16 060×10-6,Cr含量达13 333×10-6.对15个样品的可见吸收光谱进行测试及解释表明金绿宝石的可见吸收光谱是由Fe3+引起,变石的可见吸收光谱由Cr3+和Fe3+共同引起.色度学的分析和系列计算表明具有440～470 nm间最大吸收和540～630 nm宽吸收带的双峰形状的可见吸收光谱,可产生红-绿色的变石效应,通过向着该双峰形状的可见光谱的方向进行变石的优化处理可以获得宝石的变石效应.

Twenty four chrysoberyl and alexandrite samples from the major deposits all over the world were studied qualitatively by XRF and the trace elements in chrysoberyl were gotten mainly to be Fe, Ga, Ti, in alexandrite to be Fe, Cr, Ti. Half quantitative analysis of SRXRF experiments were carried out on one chrysoberyl and one alexandrite, the results indicated that in chrysoberyl Fe concentration averaged to be 17,800 × 10^-6, Cr 855 × 10 ^-6 ; in alexandrite Fe concentration averaged to be 16,060 × 10^ -6, Cr 13,333 × 10^ -6 ; and Ga was one of the very important impurity in chrysoberyl only less than Fe concentration. Optical absorption of 15 samples indicated that the absorption of chrysoberyl was induced by Fe^3 ＋ ion, of alexandrite by Fe^3 ＋ and Cr^3 ＋ together. Series chromaticity calculations were processed. The calculation results indicated that the optical spectrum which had the 540 -630 nm broad absorption band and the 440 -470 nm maximum absorption would induce red to green color-change alexandrite effect, so the treatments of alexandrite may work in the direction of getting such a visible spectrum.