Electroluminescence

From Free net encyclopedia

Electroluminescence (EL) is an optical phenomenon and electrical phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field. This is distinct to light emission resulting from heat (incandescence) or from the action of chemicals (chemoluminescence).

1 Mechanism
2 Examples of electroluminescent materials
3 Practical implementations
4 See also
5 External links

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Mechanism

Electroluminescence is the result of radiative recombination of electrons and holes in a material (usually a semiconductor). The excited electrons release their energy as photons - light. Prior to recombination, electrons and holes are separated either as a result of doping of the material to form a p-n junction (in semiconductor electroluminescent devices such as LEDs), or through excitation by impact of high-energy electrons accelerated by a strong electric field (as with the phosphors in electroluminescent displays).

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Examples of electroluminescent materials

Zinc Sulfide doped with Copper or Silver
Natural blue diamond (diamond with boron as a dopant).

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Practical implementations

Phosphor-based electroluminescent panels are frequently used as backlights to liquid crystal displays. They readily provide a gentle, even illumination to the entire display while consuming relatively little electric power. This makes them convenient for battery-operated devices such as pagers, wristwatches, and computer-controlled thermostats and their gentle green-cyan glow is a common sight in the technological world. They do, however, require relatively high voltage. For battery-operated devices, this voltage must be generated by a converter circuit within the device; this converter often makes an audible whine or siren sound while the backlight is activated. For line-voltage operated devices, it may be supplied directly from the power line. Electroluminescent night lights operate in this fashion.

In either case, the EL material must be enclosed between two electrodes and at least one electrode must be transparent to allow the escape of the produced light. Glass coated with indium oxide or tin oxide is commonly used as the front (transparent) electrode while the back electrode is or is coated with reflective metal.

Unlike neon and fluorescent lamps, EL lamps are not negative resistance devices so no extra circuitry is needed to regulate the amount of current flowing through them.

In principle, EL lamps can be made in any color but the greenish color most commonly used matches well with the peak sensitivity of human vision so it produces the greatest apparent light output for the least electrical power input.

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