2019 年 48 巻 2 号 p. 76-86
Cathodoluminescence (CL) is the emission of photons from a material stimulated by an incident electron beam. CL microscopy and spectroscopy provide useful information on the existence and distribution of lattice defects and trace elements in minerals with a spatial resolution of a few micrometers. The CL properties depend on the nature of defect and impurity centers, their concentrations, chemical composition and crystal structure of materials, which are closely related to pressure and temperature conditions during hydrothermal metasomatic reaction, shock event, and radiation damage from natural nuclides. CL of minerals, therefore, has been used as an important tool in earth and planetary sciences, as follows; (1) CL images of alkali feldspar grains in syenite (Andes, Chile) show blue, violet, pink, red, and brown colors with variable brightness. Their CL spectra exhibit a emission band assigned to Ti4＋ impurity and/or Al-O−-Al defect centers in the blue region and one to Fe3+ impurity centers in T1 and T2 sites in the red-infrared region, of which the wavelengths and intensities change depending on a kind of the microtextures in the grains. (2) CL spectra of unimplanted and He＋-ion-implanted (corresponding to natural α particles) albite (Minas Gerais, Brazil) consist of emission bands in the ultraviolet to infrared regions. The red emission intensities correlate positively with the radiation dose, implying the possibility for a geodosimetry. (3) CL images of unshocked and experimentally shocked sanidine show a red-violet color below 20.0 GPa and a blue one above 20.0 GPa. CL spectra of these shocked sanidine have ultraviolet to blue emission bands, of which intensities increase with the shock pressure. This correlation gives quantitative values of the shock pressures that alkali feldspar grains in martian meteorites have experienced. Therefore, the CL features of feldspar has a potential for a universal shock barometer with high spatial resolution.
