Cathodoluminescence,

Cathode ray tubes (CRTs) are almost universally used in colour televisions and still dominate in the display monitors of desktop computers. They are obviously not suitable for laptop PCs, because of bulk and weight, where currently liquid crystal displays are the systems of choice. Neither are they the most suitable technology for very large area displays, where other display techniques such as plasma panels and electroluminescent devices offer advantages. 

To avoid any flicker in the image, the electron beam is scanned across and down the screen, many times per second, following a predetermined set of parallel lines, the method being known as raster scanning. The phosphor dots are the picture elements or pixels and light up as the beam scans across each one. In colour televisions and monitors additive mixing of the three colours of red, green and blue produces the 

There is an alternative system, introduced by Sony as the Trinitron system, where the mask is a series of vertical slits and the phosphors are deposited in vertical stripes 

The blue phosphor of long standing is ZnS Ag, which has a radiant efficiency close to the theoretical limit. It is a donor-acceptor type phosphor, with silver ions acting as the acceptor in the ZnS with either aluminium or chlorine as the donors on zinc or sulfate sites. 

The original red phosphor was (Zn, Cd)S Ag and ZnjPO ) Mn however, it was predicted that a narrow emission around 610 nm would be beneficial. Much work resulted in the development of Eu + doped into yttrium oxides, for instance YVO Eu % YPjiEu and Yp SiEu T  

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A cathodoluminescence stage for a polarized light microscope that will take advantage of the x-rays generated by the electrons to detect the elements excited from single small (10—20-p.m) particles (EDS) is under development (see Luminescentmaterials,chemiluminescence). 

Donor and acceptor levels are the active centers in most phosphors, as in zinc sulfide [1314-98-3] ZnS, containing an activator such as Cu and various co-activators. Phosphors are coated onto the inside of fluorescent lamps to convert the intense ultraviolet and blue from the mercury emissions into lower energy light to provide a color balance closer to daylight as in Figure 11. Phosphors can also be stimulated directly by electricity as in the Destriau effect in electroluminescent panels and by an electron beam as in the cathodoluminescence used in television and cathode ray display tubes and in (usually blue) vacuum-fluorescence alphanumeric displays. 

The incoming electron beam interacts with the sample to produce a number of signals that are subsequently detectable and useful for analysis. They are X-ray emission, which can be detected either by Energy Dispersive Spectroscopy, EDS, or by Wavelength Dispersive Spectroscopy, WDS visible or UV emission, which is known as Cathodoluminescence, CL and Auger Electron Emission, which is the basis of Auger Electron Spectroscopy discussed in Chapter 5. Finally, the incoming... 

Cathodoluminescence, CL, involves emission in the UV and visible region and as such is not element specific, since the valence/conduction band electrons are involved in the process. It is therefore sensitive to electronic structure effects and is sensitive to defects, dopants, etc., in electronic materials. Its major use is to map out such regions spatially, using a photomultiplier to detect all emitted light without... 

Cathodoluminescence (CL), i.e., the emission of light as the result of electron-beam bombardment, was first reported in the middle of the nineteenth century in experiments in evacuated glass tubes. The tubes were found to emit light when an electron beam (cathode ray) struck the glass, and subsequendy this phenomenon led to the discovery of the electron. Currendy, cathodoluminescence is widely used in cathode-ray tube-based (CRT) instruments (e.g., oscilloscopes, television and computer terminals) and in electron microscope fluorescent screens. With the developments of electron microscopy techniques (see the articles on SEM, STEM and TEM) in the last several decades, CL microscopy and spectroscopy have emerged as powerfirl tools for the microcharacterization of the electronic propenies of luminescent materials, attaining spatial resolutions on the order of 1 pm and less. Major applications of CL analysis techniques include ... 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

B. G. Yacobi and D. B. Holt. Cathodoluminescence Microscopy of Inorganic Solids. Plenum, 1990. 

Spatial information about a system can be obtained by analyzing the spatial distribution of PL intensity. Fluorescent tracers may be used to image chemical uptake in biological systems. Luminescence profiles have proven useftil in the semiconductor industry for mapping impurity distributions, dislocadons, or structural homogeneity in substrate wafers or epilayers. Similar spatial infbrmadon over small regions is obtained by cathodoluminescence imaging. 

Band gaps in semiconductors can be investigated by other optical methods, such as photoluminescence, cathodoluminescence, photoluminescence excitation spectroscopy, absorption, spectral ellipsometry, photocurrent spectroscopy, and resonant Raman spectroscopy. Photoluminescence and cathodoluminescence involve an emission process and hence can be used to evaluate only features near the fundamental band gap. The other methods are related to the absorption process or its derivative (resonant Raman scattering). Most of these methods require cryogenic temperatures. 

The short-wavelength limit of the continuous spectrum is clearly a quantum phenomenon. X-ray generation by electron bombardment in principle resembles cathodoluminescence, and both processes are inverse photoelectric effects. The short-wavelength limit, Xq, discovered by Duane and Hunt6 obeys the relationship... 

Emission of light due to an allowed electronic transition between excited and ground states having the same spin multiplicity, usually singlet. Lifetimes for such transitions are typically around 10 s. Originally it was believed that the onset of fluorescence was instantaneous (within 10 to lO-" s) with the onset of radiation but the discovery of delayed fluorescence (16), which arises from thermal excitation from the lowest triplet state to the first excited singlet state and has a lifetime comparable to that for phosphorescence, makes this an invalid criterion. Specialized terms such as photoluminescence, cathodoluminescence, anodoluminescence, radioluminescence, and Xray fluorescence sometimes are used to indicate the type of exciting radiation. 

It is worth summarizing at this point the different excitation methods used for phosphors that will be referred to throughout this chapter. There are three types photoluminescence (PL) which is based on initial excitation by absorption of light, cathodoluminescence (CL) which is based on bombardment with a beam of electrons, as in a cathode ray tube (CRT) and electroluminescence (EL) which is based on application of an electric field (either a.c. or d.c.) across the phosphor. 

Fig. 36. Cathodoluminescence of a Mn-doped ZnS thin film, grown on ITO. This figure was adapted from ref. [125],...

B. Cathodoluminescence Emission produced from irradiation of (5-particles... 

ZnS CdS Zni xCdxS ZnCl2,ZnS04 CdCl2 Na2S UV, XRD, XRF, SEM, IR, RBS, Auger, SIMS, resistivity, cathodoluminescence, RHEED 1,54-56... 

All of the Type A and B inclusions studied are surrounded by a layered rim sequence of complex mineralogy [21] which clearly defines the inclusion-matrix boundary. Secondary alteration phases (grossular and nepheline, especially) are also a common feature of these inclusions, suggesting that vapor phase reactions with a relatively cool nebula occurred after formation of inclusions. Anorthite, in particular, is usually one of the most heavily altered phases the relationship between Mg isotopic composition and alteration is discussed below. (See [12] for striking cathodoluminesce photographs of typical Allende alteration mineralogy.) Inclusion Al 3510 does not fit the normal pattern as it has no Wark-rim and does not contain the usual array of secondary minerals. 

A common feature of anorthite crystals in Allende Type B inclusions is large variations (up to a factor of -v 5) in Mg content on a scale of 10 to 50 pm. (Mg variability and its correlation with Na content and cathodoluminescence color are discussed extensively in [12].) Guided by cathodoluminescence micrographs, we used the microscopic spatial resolution of the ion-probe to measure the Mg isotopic composition at several points with distinct 27Al/24Mg ratios within individual crystals from TS-21 and TS-23. Data from each individual crystal define an... 

VII. Cathodoluminescence Imaging for Elucidation of Electronic Structures of Catalysts... 

Cathodic electrodeposition coatings, 10 410 Cathodic inhibitors, 7 815 Cathodic protection, 7 804-806 Cathodic stripping voltammetry, 9 569 Cathodoluminescence microscopy, 16 484 Catholyte systems, 9 675-676... 

Microscopic techniques, 70 428 Microscopists, role of, 76 467 Microscopy, 76 464-509, See also Atomic force microscopy (AFM) Electron microscopy Light microscopy Microscopes Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) acronyms related to, 76 506-507 atomic force, 76 499-501 atom probe, 76 503 cathodoluminescence, 76 484 confocal, 76 483-484 electron, 76 487-495 in examining trace evidence, 72 99 field emission, 76 503 field ion, 76 503 fluorescence, 76 483 near-held scanning optical,... 

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