What is Electroluminecence?

From Wikipedia, the free encyclopedia

Electroluminescence (EL) is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting from heat (incandescence), from a chemical reaction (chemiluminescence), sound (sonoluminescence), or other mechanical action (mechanoluminescence).

Mechanisms

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 may be separated either by doping the material to form a p-n junction (in semiconductor electroluminescent devices such as light-emitting diodes) or through excitation by impact of high-energy electrons accelerated by a strong electric field (as with the phosphors in electroluminescent displays).

Practical implementations

he most common electroluminescent (EL) devices are composed of either powder (primarily used in lighting applications) or thin films (for information displays.)

Electroluminescent automotive instrument panel backlighting, with each gauge pointer also an individual light source, entered production on 1960 Chrysler and Imperial passenger cars, and was continued successfully on several Chrysler vehicles through 1967.

Sylvania Lighting Division in Salem and Danvers, MA, produced and marketed an EL night lamp (right), under the trade name Panelescent at roughly the same time that the Chrysler instrument panels entered production. These lamps have proven incredibly reliable, with some samples known to be still functional after nearly 50 years of continuous operation. Later in the 1960s, Sylvania's Electronic Systems Division in Needham, MA developed and manufactured several instruments for the Apollo Lunar Lander and Command Module using electroluminescent display panels manufactured by the Electronic Tube Division of Sylvania at Emporium, PA. Raytheon, Sudbury, MA, manufactured the Apollo guidance computer, which used a Sylvania electroluminescent display panel as part of its display-keyboard interface (DSKY).

Powder 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 (between 60 and 600 volts).[1] 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 nightlights operate in this fashion. Brightness per unit area increases with increased voltage and frequency.[1]

Thin film phosphor electroluminescence was first commercialized during the 1980s by Sharp Corporation in Japan, Finlux (Oy Lohja Ab) in Finland, and Planar Systems in the USA. Here, bright, long-life light emission is achieved in thin film yellow-emitting manganese-doped zinc sulfide material. Displays using this technology were manufactured for medical and vehicle applications where ruggedness and wide viewing angles were crucial, and liquid crystal displays were not well developed. In 1992, Timex introduced its Indiglo EL display on some watches.

Recently, blue-, red-, and green-emitting thin film electroluminescent materials that offer the potential for long life and full color electroluminescent displays have been developed.