Cathode ray tube phosphors

Rare earth elements have earned an important role in the CRT (cathode ray tube) phosphor industry - a highly significant one for both the color TV and the rare earth businesses. This paper will review how rare earths earned this role, and will attempt to build a framework for discussion of future use of rare earths in CRT phosphors. Color TV phosphors will be emphasized since color TV is the largest market for CRT phosphors both generally, and in particular, those which contain rare earth elements. 

Cathode ray tube phosphors with fast luminescence as well as persistent luminescence are needed in different situations. A variety of phosphors of the ZnS-CdS family are used for the purpose with Ag, Cu etc. as dopants. Other host lattices used are CaS, Zu2Si04, Y2O2S and Zn3(P04)2 typical dopants are Mn, Ce, Eu and Tb. 

Zn3(P04)2 Mn, which has an emission maximum at 635 nm, is used as a cathode-ray tube phosphor for data displays under the TEPAC number P27 and WTDS specification RE. It is produced by solid-state reaction between ZnO, MnC03, and H3P04 in an aqueous slurry. After drying, firing is carried out at 900-1150 °C for several hours in an open crucible [5.376]. 

Decay. The decay time requirements must be adhered to very precisely for cathode-ray tube phosphors. The measuring devices consist of fast excitation sources (flash lamps, lasers), photomultipliers with very low time constants, and an oscilloscope [5.440]. 

Ozawa L, Itoh M. Cathode ray tube phosphors. Chem Rev 2003 103 3835-55. 

The kinetics of the radioluminescence of organic compounds have not been widely published. Bollinger and Thomas (6) reported the room temperature decay kinetics of the long-lived scintillation component of trans-stilbene. The decay profile was non-exponential over the 100 fisec. time scale covered and, apart from intensity differences, the decay profile was identical for y-rays, neutrons and a-particles. However, the decay kinetics of several inorganic phosphors excited by low energy electrons—e.g., cathode ray tube phosphors—have been investigated (21). The theoretical treatment of the kinetics of the emission from... 

In 2000, the typical end-uses of the 454 tonnes of yttrium consumed in the USA were -70% for lamp and cathode-ray-tube phosphors, 17% for oxygen sensors, laser crystals and miscellaneous uses, 8% for ceramics and abrasives, and 5% for alloys (Hedrick 2002). 

Potassium sulfate Potassium sulfite catheter tubes, medical Styrene/methyl methacrylate copolymer cathode ray tubes, phosphor Cerium cathodes Cerium oxide... 

In colored cathode ray tubes (CRTs), such as those used in televisions and computer terminals, three electron gun beams are focused on three different sets of phosphor dots on the front face of the tube. The dots are produced by using a compHcated photoHthography process. The phosphor dots are produced by settling the three different phosphors, each of which emits one of the primary saturated colors, red, green, or blue. Each phosphor is deposited separately and the three dots in each set are closely spaced so that the three primary colors are not resolved at normal viewing distances. Instead the viewer has the impression that there is only one color, the color achieved when the three primary colors are added together. 

Uses. The main appHcation for strontium is in the form of strontium compounds. The carbonate, used in cathode ray tubes (CRTs) for color televisions and color computer monitors, is used both in the manufacturing of the glass envelope of the CRT and in the phosphors which give the color. 

Cobalt is used as a blue phosphor in cathode ray tubes for television, in the coloration of polymers and leather goods, and as a pigment for oil and watercolor paints. Organic cobalt compounds that are used as colorants usually contain the azo (51) or formazon (52) chromophores. 

Most monitors are display terminals that use cathode-ray tube (CRT) displays, which function by exciting a layer of phosphors with an electron gun. These devices include monitors used with PCs and terminals used with mainframes or minicomputers. Features such as color, resolution, and size influence power requirements. Most PC monitors are... 

Phosphors are inorganic materials which convert incident radiant energy to visible light within a device. The device chosen can be a cathode-ray tube, i.e.- a television tube, or a fluorescent lamp. A phosphor consists of a matrix modified by an additive chosen so that it becomes optically active within the matrix, or compound. This is an example of a substitutional impurity in a lattice wherein the additive, usualty Ccdled an "activator", introduces a lattice defect that is optically active. However, the added impurity still follows all of the rules found for defects in a lattice, as shown by the following example. 

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. 

In the previous chapter we have introduced the physical basis of the interpretation of optical spectra of centers in crystals. The main effect of these centers is to introduce new energy levels within the energy gap of the crystal, so that the transitions among these levels produce new optical bands that are not present in the perfect crystal. Due to these absorption and emission bands, centers in crystals are relevant for a variety of applications, such as solid state lasers, amplifiers and phosphors for fluorescent lighting and cathode ray tubes. In this chapter, we will describe the main characteristics of the relevant centers for these applications. 

Mn + ions (3d electronic configuration) are shown to produce a broad luminescence in more than 500 inorganic compounds, covering a wavelength range from about 490 nm to about 750 nm. Although this ion is not of relevance for laser applications, it is widely used in the phosphor screens of cathode ray tubes and in fluorescent lamps. 

There are not many uses for dysprosium. Scientists continue to experiment with it as a possible alloy metal (it has a high melting point) to be mixed with steel to make control rods that absorb neutrons in nuclear reactors. There are only a few commercial uses for dysprosium, such as a laser material and as a fluorescence activator for the phosphors used to produce the colors in the older TV and computer cathode ray tubes (CRTs). When combined with steel or nickel as an alloy, it makes strong magnets. 

Hematite is used to coat the red emiting phosphor, Y2O2EU, which is used in cathode ray tubes (Franz et al., 1993 Merckhi and Feldmann, 2000). Hematite is also used in sensors for the detection of hydrocarbon gases and carbon monoxide. The sensitivity of the sensor can be improved by sintering the oxide with 0.09 mol ° mol Al at 850 °C (Han et al., 2001 and references therein). 

Phosphors are also widely used in many other cathode ray tubes, for example, in... 

The results of their decay-time measurements are summarized in Table IX. The measurements were made using either cathode-ray or ultraviolet excitation. For the emissions excited by cathode rays the technique of Bril and Klasens (750) was employed. The ultraviolet excitation was accomplished with a cathode-ray tube equipped with a fast ultraviolet-emitting phosphor. 

Industrial silver-activated zinc sulfide phosphors use the intense blue emission exclusively. The ZnS Ag phosphor for cathode ray tubes is obtained by firing zinc sulfide and silver nitrate at ca. 1000 °C in the presence of sodium chloride (coactivator Cl-) [5.318]. The afterglow can be further reduced by addition of 10-3-10-4% of nickel ions. 

Multiple activation of zinc sulfide is also possible. Zinc-cadmium sulfide, doubly activated with silver and gold, which is used as a white-luminescing, one-component phosphor for monochromic cathode-ray tubes [5.334], and the yellow-luminescing ZnS Cu, Au, A1 phosphor, whose emission color corresponds to that of Zn, x Cdx S Cu [5.332], are known. 

ZnO Zn is a typical example of a self-activated phosphor. In the case of zinc oxide, it is an excess of zinc which enables the phosphor to luminesce. The production is carried out by thermal oxidation of crystallized zinc sulfide in air at ca. 400 °C. The green luminescence, with a broad maximum at 505 nm, has a very short decay time of 10-6 s. As a phosphor for cathode-ray tubes, ZnO.Zn is classified in the TEPAC list as P 24 and in the WTDS system as GE. 

Phosphors are an important, quality-determining component of cathode-ray tubes (Fig. 87). In the phosphor screen, modulated electrons are converted into a visible image. 

Cathode-ray tubes have a very large number of applications which require varying phosphor qualities. Table 58 lists the most important cathode-ray luminescent pigments. 

The Worldwide Phosphor Type Designation System (WTDS) the optical data of the specifies phosphors for cathode-ray tubes [5.429]. It replaces several phosphor designation systems (e.g., TEPAC, Pro Electron) previously in use in various countries. The phosphors are characterized by two capital letters, the first giving the position of the emission color in the Kelly Charts of Color Designation ... 

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