chemoftv - The Chemistry of Television (and Other Display...

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The Chemistry of Television (and Other Display Technologies) Amy Walker Department of Chemistry, Washington University http://www.chemistry.wustl.edu/~walker
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-OR ±- How do televisions work? http://www.willothewisp.co.uk/
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Introduction There are many different display technologies: & CRT &LCD & Plasma Screen & PLED / OLED & ±±. . All of these rely on chemistry to make them work!
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Cathode Ray Tubes (CRTs) & The ±oldest² television/display technology. & CRT first proposed in 1908 by Campbell Swinton. &Bu in ³ January 1926 John Logie Baird demonstrated a ±televisor², a mechanical television. & 1928 Farnsworth demonstrates a CRT system to the press in San Francisco. & 1936 RCA demonstrate all electronic TV with 343 lines, 30 frames per second. http://www.arts.uwaterloo.ca/FINE/juhde/hills961.htm; http://www.tvhistory.tv/pre-1935.htm
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Cathode Ray Tubes (CRTs) How do they work? Every image on a television screen is made up of a series of spots, pixels. By rastering, or scanning, each pixel, a moving image can be made. As the scanning speed increases we see the image due to a property of our eyes called persistence of vision . Zoom Zoom Scanning Speed
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Cathode Ray Tubes (CRTs) How do they work? Magnets Electron Beam In a cathode ray tube (CRT), an electron beam is generated. The beam is then steered by magnets to hit the front screen. Screen When the electron hits the front screen, it strikes a phosphor , which then lights up. The higher the electron current, the brighter the phosphor glows.
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Cathode Ray Tubes (CRTs) How do they work? How about color? You need only three primary light colors: red , green and blue . This does not work like the primary colors described in an art class. Why? A yellow object adsorbs blue light , but reflects green and red light . So we see a yellow object.
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Cathode Ray Tubes (CRTs) How do they work? A color television has three different phosphors for every pixel, which glow red , green and blue .
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Cathode Ray Tubes (CRTs) What is a Phosphor? Phosphors are substances which emit light when the substance is excited. Excitation can be electrical, due to light or due to a chemical reaction. Light persists after excitation (if it doesn&t - fluorescent.) Y 2 O 2 S:Eu Y 2 O 2 S:Eu + pigment ZnS:Cu,Al ZnS:Cu,Au,Al ZnS:Ag ZnS:Ag + pigment ZnS:Ag,Cl ZnS:Ag,Cl + pigment ZnS:Ag,Al ZnS:Ag,Al + pigment Red Green Blue e - e - Light Energy How?
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Plasma Displays One of the problems with CRTs is that they use a lot of power and so can not be made to be really large. One solution is to use a plasma display . http://www.plasmatvbuyingguide.com/plasmatv-howwork9.html; http://www.activelight.com/about_ActiveLight/about_technology.asp?X=1 A plasma display is split up into many pixels & just like a CRT & but in this case each cell is a low pressure gas cell filled with neon and xenon. At the back of the cell is a red, green or blue phosphor.
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This note was uploaded on 03/27/2011 for the course CHEM 2211L taught by Professor T.a. during the Spring '08 term at University of Georgia Athens.

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chemoftv - The Chemistry of Television (and Other Display...

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