Cathodoluminescence Microcharacterisation of Silicon Dioxide Polymorphs

Abstract

Optical cathodoluminescence (CL) microscopy and CL microanalysis are useful characterization techniques in the geosciences (Yacobi and Holt 1990; Remond et al. 1992a, 1997; Hagni 1987): Information on the distribution of defects (e.g. impurities) in minerals, obtained from optical CL microscopy, may be complemented by CL microscopy and spectroscopy (i.e. microanalysis) in an electron microscope. The focused electron beam in the electron microscope is typically submicron in diameter. The diameter of the electron beam produced by the cold cathode electron gun in the optical CL microscope is typically of order 1–10 mm in diameter (Yacobi and Holt 1990), thus the power density delivered to the specimen is usually greater during CL microanalysis. In a scanning electron microscope (SEM), the CL spectra may be collected from a larger region by defocusing the beam or scanning the beam over an area of the specimen. This has the effect of reducing electron irradiation induced effects (i.e. irradiation damage, heating effects), and averaging submicron sized inhomogeneities. CL microanalysis in a SEM provides high sensitivity (parts per million, ppm) high resolution (µm), and detection of defect centers in luminescent materials (Yacobi and Holt 1990; Remond et al. 1992a). Following the identification of the defects associated with the emission bands in the CL spectrum, the distribution of each luminescent center may be imaged with high spatial resolution using monochromatic CL microscopy. CL microanalysis also complements defect structure information available from other spectroscopies such as photoluminescence (PL), thermoluminescence (TL or TSL), electron spin resonance (ESR), and optical absorption (OAS) spectroscopies. CL microanalysis is a powerful technique ideally suited for investigating the microscopic distribution of impurities and other defects in luminescent materials.