In this review, we present analysis of absorption and circular dichroism spectra of disordered langasite crystals with the calcium gallium germanate structure, whose structures have no screw axis. We consider results of original research concerned with spectroscopic characteristics of undoped and transition metal-doped langasite crystals. Structural disordering on a site leads to charge disbalance on this site and defect formation. Electron transitions to “defect” states contribute to both absorption and circular dichroism spectra. In this situation, a transition metal ion can be incorporated into a “defect” site in different oxidation states, depending on the type of position and the impurity ion. It has been shown that electric dipole forbidden but magnetic dipole allowed electron transitions of impurity ions of d-block elements have the highest intensity in the circular dichroism spectra of doped crystals.

中文翻译：

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过渡金属离子掺杂的无序菱铁矿的光谱学

在这篇综述中，我们介绍了具有锗酸镓镓结构的无序菱铁矿晶体的吸收和圆二色性光谱的分析，该结构没有螺旋轴。我们考虑了与未掺杂和过渡金属掺杂的铜硅酸盐晶体的光谱特性有关的原始研究结果。一个位置上的结构混乱会导致该位置上的电荷失衡和缺陷形成。电子跃迁到“缺陷”态有助于吸收和圆二色性光谱。在这种情况下，取决于位置和杂质离子的类型，过渡金属离子可以以不同的氧化态掺入“缺陷”部位。研究表明，电偶极子是被禁止的，而磁偶极子则允许d的杂质离子的电子跃迁元素在掺杂晶体的圆二色性光谱中具有最高强度。