为揭示绿色电气石的致色机理, 对阿富汗浅绿色电气石开展了宝石学常规测试、 X射线衍射、 红外光谱、 紫外-可见光谱、 X射线光电子能谱和电子探针等一系列研究。 结果表明, 该电气石相对密度为3.04, No=1.639, Ne=1.620, 多色性弱; 衍射分析表明其为锂电气石; 红外光谱在456, 500, 605, 645, 715, 780, 980, 1 030, 1 110, 1 290, 1 350, 3 460, 3 580和3 640 cm^-1等处出现吸收峰, 其中605, 645, 715, 780和1 110 cm^-1吸收峰由Si—O—Si对称及非对称伸缩振动引起, 980和1 030 cm^-1吸收峰由O—Si—O对称及非对称伸缩振动引起, 500 cm^-1吸收峰由Si—O弯曲振动引起, 1 290 cm^-1吸收峰由[BO₃]伸缩振动引起, 1 350 cm^-1吸收峰由OH弯曲振动引起, 3 460和3 580 cm^-1处吸收峰由O3H振动引起, 3 640 cm^-1处吸收峰由O1H振动引起, 456 cm^-1吸收峰强度大, 源自[AlO₆]振动。 红外光谱中605和645 cm^-1吸收峰与标准谱图的差异可能反映出致色离子的混入对[Si₆O₁₈]振动产生一定影响。 衍射分析和红外光谱分析的结果揭示出浅绿色产生的晶体结构基础。 在可见光范围内该电气石在E∥c和E⊥c方向的吸收位置基本相同, 仅吸收强度略有差异, 从而导致其多色性弱, 在红区718 nm和蓝紫区420 nm处均形成吸收, 而在黄绿区则透射良好, 因此呈现其特有的明亮的浅绿色。 紫外-可见光谱分析揭示出浅绿色的颜色结构。 X射线光电子能谱表明该电气石主要含有Li, Na, Al, Si, O, F和B等元素, 微量元素为过渡金属离子Fe²⁺, Fe³⁺, Mn²⁺和Ni²⁺等, 并且Fe²⁺, Fe³⁺和Ni²⁺占据Y位, 而Mn²⁺占据Z位。 XPS分析揭示出产生浅绿色的过渡金属离子种类、 价态、 占位等化学状态。 结合电子探针分析, 样品的晶体化学式为: ^X(Na_0.612Ca_0.063K_0.008) ^Y(Li_0.989Fe0.0702+Fe0.1173+Al_1.824) ^Z(Mn0.0352+Al_5.762Si_0.203)[Si_6.000O₁₈][BO₃]₃ ^V(OH_2.134O_0.866)^W(OH_0.542F_0.458)。 电子探针分析揭示出浅绿色产生的晶体化学组成。 样品紫外-可见吸收谱峰和其化学组分及过渡金属离子化学状态的特征综合表明, 718 nm处吸收可能系由Fe²⁺-Fe³⁺的电荷转移引起, 而420 nm处吸收则可能由Ni²⁺的 d— d电子跃迁引起。 上述研究结果能为以致色离子化学状态为基础的改色优化、 以晶体化学及谱学特征为基础的产地鉴定等提供可靠依据。

In this paper, the coloration mechanism of green tourmaline was determined by conducting a series of tests on the light green tourmaline mined from Afghanistan, including routine gemological tests, XRD analysis, FTIR Analysis, UV-Vis spectral analysis, XPS analysis, and electron probe microanalysis. The results showed that the tourmaline has a relative density of 3.04, an ordinary refractive index (No) of 1.639, an extraordinary refractive index (Ne) of 1.620, and weak pleochroism. XRD analysis indicated that it is lithium tourmaline. FTIR spectra showed absorption peaks at 456, 500, 605, 645, 715, 780, 980, 1 030, 1 110, 1 290, 1 350, 3 460, 3 580 and 3 640 cm^-1, etc. Among them, the peaks at 605, 645, 715, 780, and 1 110 cm^-1 were caused by the symmetric and asymmetric stretching vibrations of Si—O—Si; the peaks at 980 and 1 030 cm^-1 were caused by the symmetric and asymmetric stretching vibrations of O—Si—O; the peak at 500 cm^-1 was caused by the bending vibrations of Si—O; the peak at 1 290 cm^-1 was caused by the stretching vibrations of [BO₃]; the peak at 1 350 cm^-1 was caused by the bending vibrations of OH; the peaks at 3 460 and 3 580 cm^-1 were caused by O3H vibrations; O1H vibrations caused the peak at 3 640 cm^-1; and the strong peak at 456 cm^-1 was caused by [AlO₆] vibrations. The differences between the absorption peaks at 605 and 645 cm^-1 in the measured FTIR spectrum and those in the standard FTIR spectrum may indicate that the presence of color-producing ions has some impact on [Si₆O₁₈] vibrations. XRD and FTIR analyses revealed the underlying crystal structure resulting in the light green color. In the visible light range, the absorption peaks of the tourmaline in E∥c and E⊥c directions are roughly at the same position, and only differ slightly in absorption intensity, which results in weak pleochroism of the tourmaline. Absorption was found at both 718 nm in the red region and 420 nm in the blue-violet region, whereas good transmission was detected in the yellow-green region, which produced the tourmaline's unique color of bright light green. UV-Vis spectral analysis revealed the color structure of the light green. XPS analysis showed that the tourmaline mainly contains Li, Na, Al, Si, O, F, B, and other elements. It also contains traces of transition metal ions such as Fe²⁺, Fe³⁺, Mn²⁺, and Ni²⁺, of which Fe²⁺, Fe³⁺, and Ni²⁺ occupy the Y site and Mn²⁺ occupies the Z site. XPS analysis revealed the types, valence states, occupancy, and other chemical states of the transition metal ions that produce the light green color. In combination with the results of electron probe microanalysis, the crystal chemical formula of the sample can be estimated as ^X(Na_0.612Ca_0.063K_0.008) ^Y(Li_0.989Fe0.0702+Fe0.1173+Al_1.824) ^Z(Mn0.0352+Al_5.762Si_0.203)[Si_6.000O₁₈][BO₃]₃ ^V(OH_2.134O_0.866) ^W(OH_0.542F_0.458). Electron probe microanalysis revealed the chemical composition of the crystal responsible for the production of light green. Comprehensive analysis of the UV-Vis spectrum and chemical components of the sample as well as the chemical states of the transition metal ions contained in the sample suggested that the absorption at 718 nm may be caused by charge transfer from Fe²⁺ to Fe³⁺, where the absorption at 420 nm may be caused by the d— d electron transition of Ni²⁺. These study results may provide a reliable basis for color change optimization based on the chemical state of color-producing ions and the place of origin identification based on crystal chemistry and spectroscopic characteristics.