Colour television

Group III with electronic configuration 5s 4d . The principal ore is gadolinite (a silicate also containing lanthanides). Y2O3 containing Eu is used as a red phosphor in colour television. Yttrium iron garnets are used as microwave filters. 

Some oxide-type minerals have been found to luminesce when irradiated. A simple example is ruby (aluminium oxide with chromium activator), which emits bright-red light. The phosphors are incorporated into colour television screens to emit the colours blue (silver-activated zinc sulphide), green (manganese-activated zinc orthosilicate), and red (europium-activated yttrium vanadate). 

It is obvious that the narrow band thermoluminescence 8, 9) influenced Carl Auer von Welsbach in developing his mantle between 1884 and 1892, but as discussed in the next chapter, the optimized conditions for white gas-light rather involve another t cpe of excited states of cerium(IV). On the other hand, the cathodo-luminescence in narrow bands discovered by William Crookes and carefully studied by Urbain [12) corresponds to internal transitions in the partly filled shell. Thus, the excited state of 4/ europium(III) produces the red emission (important for colour television) in the orthovanadate [13) Yi Eux VO 4 and in the oxysulphide (74) by transitions to " Fz, and Fq. Certain... 

Additive colour mixing applies to the combination of light beams and is therefore the system employed in colour television and other display systems (see Chapter 3). 

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... 

The CIE chromaticity diagram for the desired red, green and blue phosphors in colour television is given in Figure 3.5. There is some tolerance level around the... 

Figure 3.5 CIE chromaticity diagram for the desired phosphors in colour television.

Both types of europium ion are incorporated into the phosphors used in colour television screens and computer monitors. Phosphors are substances that emit light when struck by a beam of electrons. The electron beam stimulates electrons in the atomic constituents of the phosphor into states of greater energy, from which they decay back to their initial state by radiating away the excess energy as visible light. 

The fluorescence properties of europium compounds offer another possibility for using them as a red component in colour television tubes. As all fluorescence compounds are not capable of producing laser action, they still stand a chance of being used as phosphors. Those phosphors which have a main emission peak between 6110 and 6140 A are the only ones suitable. The cathodoluminescence properties of several Eu3+ doped GdaOs and YVO4 proved to be highly efficient red emittors for colour... 

Such delay lines are used in colour television sets to introduce a delay of approximately 64 /rs, the time taken for the electron beam to travel once across the screen. The delayed signal can be used to average out variations in the colour signal that occur during transmission and so improve picture quality. Similar delay lines are used in videotape recorders. 

Colour televisions and similar displays are the largest commercial market for lanthanide phosphors, with over 100 million tubes manufactured a year. About 2 g of phosphor is used in each tube. The lanthanide involvement in a traditional colour TV tube works along these... 

The two mineral sources for strontium are the sulfate (celes-tite) and carbonate (strontianite). In 2001, 75% of strontium used in the US went into the manufacture of faceplate glass in colour television cathode-ray tubes in order to stop X-ray... 

The two mineral sources for strontium are the sulfate (celes-tite) and carbonate (strontianite). The main use of strontium is as a component in colour television faceplate glass ( 8% SrO is incorporated into the glass) where its function is to stop X-ray emissions from the cathode ray tube (CRT). However, the increasing market for CRT-free flat-screen televisions is having a dramatic effect on the demand for strontium. Other uses of strontium include ferrite ceramic magnets and pyrotechnics (see Flame tests in Section 12.3). 

Indium sulfide is a wide bandgap semiconductor, which has application as photocatalyst, phosphor material for colour televisions and in optoelectronic devices. Pejova and Bineva reported the sonochemical... 

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