Cathodoluminescence

Cathodoluminescence is a special form of luminescence, in which an incoming electron from an electric source is incident on a solid surface and this stimulates light, ie emit electromagnetic radiation, ( functional principle of the Braun tube or cathode ray tube ).

Applications and experimental setups

In geology, mineralogy, and materials science an optical Kathodolumineszenzmikroskop is used to make internal structures of rock samples, ceramics, glasses, etc. visible and thus to obtain information about the structure, the origin and the quality of the material examined.

In materials science and semiconductor technology Kathodolumineszenzuntersuchungen often in a scanning electron microscope (SEM ) can be performed. And where a highly focused electron beam on the sample and causes them to depending on the material to emit light from the infrared, visible or UV range. This light is collected by an optical system, such as an elliptical mirror. Via an optical system, it is passed out of the SEM and directed through a monochromator on a detector ( photomultiplier tube or CCD detector ). In this case, luminescence can be received either as a function of wavelength of light / photons energy or it may be at a particular wavelength of a luminescence image are recorded, which then can be directly correlated with a secondary electron image of the surface. This information allows conclusions about the structure and quality of the investigated semiconductor crystals.

Although an electron microscope with a Kathodolumineszenzanbau allows much higher magnifications, but is more difficult to handle and far more expensive than an optical Kathodolumineszenzmikroskop whose strength is to show the actual visible luminescence of the samples directly through the eyepiece. The former is characterized in particular for the investigation of nanostructured semiconductors of importance, while the latter just is used in geology.

The shadow cross tube is found still in the physics lessons at school and college as a demonstration device. It allows reference to the luminescence of the bulb glass or a luminescent screen the study of the generation, propagation and the magnetic influence of cathode rays.

Examples of technical applications

• Picture tubes for televisions and CRT monitors
• A vacuum fluorescent display (VFD), and digitron
• Magic Eye ( Abstimmanzeigeröhre )

History

As the discoverer of cathodoluminescence applies the Ukrainian physicist Johann Puluj. He developed a lamp in 1881, later known as Pulujlampe, which was based on the principle of cathodoluminescence. Philipp Lenard was awarded in 1905 " for his work on cathode rays " the Nobel Prize for physics. In his honor, cathodoluminescent substances are also known as Lenard phosphors.