Cathodoluminescence is an optical and electrical phenomenon whereby a beam of electrons is generated by an electron gun (e.g. cathode ray tube) and then impacts on a luminescent material such as a phosphor, causing the material to emit visible light. The most common example is the screen of a television. In geology, mineralogy and materials science an optical cathodoluminescence microscope is used to examine internal structures of rocks, ceramic, glass etc. in order to get information on the composition, growth and quality of the material. An optical phenomenon is any observable event which results from the interaction of light and matter. ... Electrical phenomena are commonplace and unusual events that can be observed which illuminate the principles of the physics of electricity and are explained by them. ... A phenomenon (plural: phenomena) is an observable event, especially something special (literally something that can be seen from the Greek word phainomenon = observable). ... Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ... Electron gun from a cathode ray tube An electron gun is a component that produces an electron stream that has a precise kinetic energy, being used in all TVs and monitors which use cathode ray tube technology, and in other instruments, eg. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT The cathode ray tube or CRT, invented by Karl Ferdinand Braun, is the display device that is traditionally used in most computer displays, video monitors, televisions and oscilloscopes. ... A phosphor is a substance that can exhibit the phenomenon of fluorescence (glowing during absorption of radiation of another kind) or phosphorescence (sustained glowing without further stimulus). ... A cathodoluminescence (CL) microscope combines methods from electron and regular (light optical) microscopes. ...

Cathodoluminescence occurs because the impingement of a high energy electron beam onto a semiconductor will result in the promotion of electrons from the valence band into the conduction band, leaving behind a hole. When an electron and a hole recombine, it is possible for a photon to be emitted. The energy (color) of the photon, and the probability that a photon and not a phonon will be emitted, depends on the material, its purity, and its defect state. In this case, the "semiconductor" examined can, in fact, be almost any non-metallic material. In terms of band structure, classical semiconductors, insulators, ceramics, gemstones, minerals, and glasses can be treated the same way. Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... In solids, the valence band is the highest range of electron energies where electrons are normally present at zero temperature. ... In semiconductors and insulators, the conduction band is the range of electron energy, higher than that of the valence band, sufficient to make the electrons free to accelerate under the influence of an applied electric field and thus constitute an electric current. ... In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field, for instance light. ... In physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the atomic lattice of a solid. ... In solid state physics, the electronic band structure, or simply band structure, refers to the dispersion relation (the relation between energy versus momentum) of electrons in a crystal. ...

In materials science and semiconductor engineering, cathodoluminescence will mostly be performed in either a scanning electron microscope or a scanning transmission electron microscope. In this case, the highly focused beam of electrons impinges on a sample and induces it to emit light from a localized area. This light will be collected by an optical system, such as an elliptical mirror. From there, a fiber optic will transfer the light out of the microscope where it will be separated by a monochromator and then detected with a photomultiplier tube. By scanning the microscope's beam in an X-Y pattern and measuring the light emitted with the beam at each point, a map of the optical activity of the specimen can be obtained. The primary advantages to the electron microscope based technique is the ability to resolve features down to 10-20 nanometers, the ability to measure an entire spectrum at each point (hyperspectral imaging) if the photomultiplier tube is replaced with a CCD camera, and the ability to perform nanosecond- to picosecond-level time-resolved measurements if the electron beam can be "chopped" into nano- or pico-second pulses. However, as the abilities are improved, the cost of the electron-microscope based techniques becomes very high. These advanced techniques are useful for examining low-dimensional semiconductor structures, such a quantum wells or quantum dots. Low temperature SEM magnification series for a snow crystal. ... A scanning transmission electron microscope (STEM) is a type of transmission electron microscope. ... A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light chosen from a wider range of wavelengths available at the input. ... Photomultipliers, or photomultiplier tubes (PMT) are extremely sensitive detectors of light in the ultraviolet, visible and near infrared. ... In most modern usages of the word spectrum, there is a unifying theme of a variety of possible cases between extremes at either end. ... Imaging spectroscopy is defined as being the simultaneous acquisition of spatially coregistered images, in many, spectrally contiguous bands, in an internationally recognized system of units from a remotely operated platform (Schaepman, 2005). ... A charge-coupled device (CCD), is an integrated circuit containing an array of linked, or coupled, capacitors. ... A quantum well is a potential well that confines particles in one dimension, forcing them to occupy a planar region. ... A quantum dot is a potential well that confines electrons in three dimensions to a region of the order of the electrons de Broglie wavelength in size, a few nanometers in a semiconductor. ...

Although direct bandgap semiconductors such as GaAs or GaN are most easily examined by these techniques, indirect semiconductors such as silicon also emit weak levels of light, and can be examined as well. In particular, the luminescence of dislocated silicon is different from intrinsic silicon, and can be used to map defects in integrated circuits. In semiconductor physics, a direct bandgap means that the conduction band lies directly above the valence band, in momentum space (see E-k plots). ... Gallium arsenide (GaAs) is a chemical compound composed of gallium and arsenic. ... Gan can have several meanings: A Romanization of the Chinese character 甘 (Gān), an abbreviation for Gansu Province in the Peoples Republic of China A Romanization of the Chinese character 赣 (Gàn), an abbreviation for: The Gan River Jiangxi Province in the Peoples Republic of China, through which... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... For the syntaxic operation, see Dislocation (syntax) For the medical term, see Dislocation (medicine) In materials science a dislocation is a linear crystallographic defect, or irregularity, in crystal structure. ... An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ...

Except of the much higher magnification and good versatility, an electron microscope with a cathodoluminescence detector will be more complicated and more expensive compared to an easy to use optical cathodoluminescence microscope which benefits from its ability to show actual visible color features immediately through the eyepiece. A cathodoluminescence (CL) microscope combines methods from electron and regular (light optical) microscopes. ...

In short, cathodoluminescence is a technique that can be implemented in an optical or electron microscope with the proper accessories, and allows the optical properties of non-metallic materials to be examined.