Cathodoluminescence is a special form of luminescence in which an electron beam coming from an electron source hits a solid surface and stimulates it to emit light, i.e. electromagnetic radiation (functional principle of cathode ray tube).
In geology, mineralogy and materials science, an optical cathodoluminescence microscope is used to visualize internal structures of rock samples, ceramic materials, glasses, etc., and thus to obtain information about the structure, formation and quality of the material under investigation.
Cathodoluminescence studies are often performed in a scanning electron microscope (SEM). Here, a highly focused electron beam hits the sample and causes it to emit light from the infrared, visible or UV range, depending on the material. This light is collected by an optical system, such as an elliptical mirror. It is guided out of the SEM via optics and directed by a monochromator to a detector. Either luminescence spectra can be recorded as a function of the light wavelength/photon energy or an image of the luminescence can be recorded at a certain wavelength, which can then be directly correlated with a secondary electron image of the surface. This information allows conclusions to be drawn about the structure and quality of the semiconductor crystals under investigation.
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An electron microscope with a cathodoluminescence mount allows significantly higher magnifications, but is more difficult to handle and far more expensive than an optical cathodoluminescence microscope, whose strength lies in showing the actually visible luminescence colors of the samples directly through the eyepiece. The former is therefore particularly important for the investigation of nanostructured semiconductors, while the latter is used in geology.
The shadow cross tube can still be found in physics lessons at schools and universities as a demonstration device. It allows the study of the generation, propagation and magnetic influence of cathode rays on the basis of the luminescence of the piston glass or a fluorescent screen.
CRT televisions and CRT monitors, Vacuum fluorescence display (VFD) etc are examples of application of the technology.
