Phosphors for X-ray

The principal uses of tungsten compounds lie outside the scope of this chapter (e.g. catalysts for oil refining). WS2 is an effective additive for lubricating oils.41 CaW04 is used as a phosphor for X-ray screens.42 W03 is almost as effective as Mo03 as a flame retardant for poly(vinyl chloride).5... 

Other applications for the lanthanides include phosphors for X-ray screens and television tubes, catalysts, lasers, powerful magnets, and high-temperature superconductors. 

The applications and mechanisms of PSL phosphors for X-ray imaging were described by Crawiford and Brixner (1991). The paper depicts the requirements and the mechanisms of high PSL efficiency phosphors. It deals mainly with BaFCLEu and BaFBnEu. ... 

Divalent europium-activated BaECl was the first rare-earth-activated x-ray phosphor (24). The advantage of BaECLEu " over the conventional CaWO material is in the higher x-ray absorption and better x-ray-to-visible light conversion. The problem with BaECl for x-ray appHcation is in the lower density (4.56 g/cm vs 6 g/cm for CaWO and plate-like morphology. 

CdS and CdSe are also useful phosphors. CdTe is a semiconductor used as a detector for X-rays and y-rays, ° and mercury cadmium tellurideriri has found widespread (particularly military) use as an ir detector for thermal imaging. 

The phosphor has the following characteristics which are suitable to obtain a high-quality image with a low X-ray dose 1) the absorption coefficient for X-rays is high, 2) PSL radiation is efficiently released under such visible-light stimulation as a He Ne laser beam, 3) the PSL-radiation spectrum falls within the range of... 

Phosphor manufacture is still a dominant factor for suppliers of rare earth chemicals. According to industry sources (29), approximately 1/3 of the monetary volume of rare earth chemicals is used by the electronics industry. Included in this figure is Sm O for samarium-cobalt magnets. The remainder includes Gd O, La.,0 and Tb 0, for x-ray and lighting phosphors, and Y O ana... 

For X-ray excitable phosphors, the intensifier effect is tested as a measure of the luminescence yield. A very simple process uses the exposure of blue- or green-sensitive films. The phosphor is excited by X rays in a cell covered with a light-sensitive film. The blackening of the film is measured with a densitometer and, for given excitation conditions, is a measure of the efficiency of the phosphor. 

For medical (X-ray) and military (infrared) uses, X-ray and IR fluorescence and image intensifiers were developed. An input phosphor converts X-ray (or IR) photons to electrons, which are electronically intensified and... 

Obviously, the dissolution of the elements leads to change in the crystal lattice and the mineral composition. This can well be seen during the acidic treatment of montmorillonite or bentonite for catalytic purposes (Section 2.1). The treatment is done using concentrated hydrochloric, sulfuric, or phosphoric acid. X-ray diffraction studies show that a commercially available montmorillonite has low montmorillonite content (53%). The other constituents are illite 10%, kaolinite 6%, quartz 10%, plagioclase 5%, gypsum 1%, anhydrite 4%, and amorphous 7%. 

The barium fluorohalides BaFCl and BaFBr are of practical interest as matrices for X-ray storage phosphors. The Ba NMR spectra of both compounds have been reported and their NMR interaction parameters determined (B as tow and Stuart 1996). The room temperature xq value of BaFCl is relatively small but increases rapidly with temperature, possibly due to variations in the thermally averaged structure about the Ba nucleus. The room temperature xq value of BaFBr is larger by a factor of 10 than that of BaFCl, and its Ba linewidth was such that the spectrum had to be determined by the stepped-frequency method, by contrast with the static BaFCl spectrum which was sufficiently narrow that the whole transition could be excited by ordinary pulse spectroscopy (Bastow and Stuart 1996). 

Use Lanthanum salts, electronic devices, pyrophoric alloys, rocket propellants, reducing agent catalyst for conversion of nitrogen oxides to nitrogen in exhaust gases (usually in combination with cobalt, lead, or other metals), phosphors in x-ray screens. 

Use Pigment, white and opaque glass, base for color lakes, rubber, plastics, dyeing (hydrosulfite process), ingredient of lithopone, phosphor in X-ray and television screens, luminous paints, fungicide. 

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