Phosphor computer terminal

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. 

The blue-emitting component of most television screens and computer terminals is another sulfide, ZnS Ag,Al. Although rare-earth activated blue-emitting phosphors ZnS Tm " and Sr (P0 2d-Eu (30) have also been evaluated for this appHcation, the search for a good blue phosphor that does not saturate at high current densities and maintains weU continues. 

An already substantial and rapidly growing market for CRT phosphors and tubes is in the area of data displays, both alphanumeric and graphic, e.g., computer terminals and word processors. In spite of dramatic advances in other technologies, CRT s are still the most cost effective way to present information, and very likely always will be. Most data display tubes do not use rare earth phosphors because of their high cost, rare earth phosphors find use only when there is a compelling need for their special properties. At the present time, this is limited to the use of Eu3+ reds in tricolor tubes that use the same shadow mask principle as conventional color TV. 

CRT, the abbreviation for cathode-ray tube, was once a familiar acronym. Before liquid crystal display (LCD) was available, the CRT was the heart of computer monitors and TV sets. The first cathode-ray tube was made by Michael Faraday (1791-1867) about 150 years ago. When he passed electricity through glass tubes from which most of the air had been evacuated, Faraday discovered cathode rays, a type of radiation emitted by the negative terminal or cathode. The radiation crossed the evacuated tube to the positive terminal or anode. Later scientists found that cathode rays travel in straight lines and have properties that are independent of the cathode material (that is, whether it is iron, platinum, and so on). The construction of a CRT is shown in Figure 2-6. The cathode rays produced in the CRT are invisible, and they can be detected only by the light emitted by materials that they strike. These materials, called phosphors, are painted on the end of the CRT so that the path of the cathode rays can be revealed. Fluorescence is the term used to describe the emission of light by a phosphor when it is struck by... 

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