LED and Phosphor displays are now popular which uses the principle of Electroluminescence. It is the property of the semiconductor to release energy in the form of Photons. Electroluminescence results from the radiative recombination of electrons and holes by the influence of an electric charge. In the LED, the doping material forms the p-n junction which separates the electrons and holes. When current passes through the LED, the recombination of electrons and holes takes place resulting in photon emission. But in Phosphor displays, the mechanism of light emission is different. By the influence of the electric charge, the electrons are accelerated leading to the emission of light.
One typical application of EL device is the panel lighting like automotive dash board panel. It is also used in Audio equipments and other electronic gadgets having displays. In some makes of Laptops, Powder Phosphor panel is used as the back-light. The lighting of EL device is more superior than that of LCD. It is also used in Keypad illumination, Watch dials, Calculators, Mobile phones etc. The power consumption of EL display is very low so that it is an ideal solution to save power in battery operated devices. The color of EL display may be Blue, Green, White etc.
EL Display appears to be brighter than LED display and the brightness of the surface appears the same from all angle of view. The light from the EL display is not directional so that it cannot be measure in Lumens. The light from the EL display is Monochromatic and has very narrow bandwidth and is visible from a long distance. The EL light can be perceived well since the light is homogenous. The voltage applied to the EL device controls the light output. When the voltage and frequency increases, the light output will also increases proportionally.
The EL devices consist of a thin layer or material either organic or inorganic doped with a semiconductor material. It also contains do-pants to give color. Typical substances used in EL devices are Zinc Sulphide doped with Copper or Silver, Blue diamond doped with Boron, Gallium Arsenide etc. To give Yellow-Orange light, the do-pant used is Zinc and Manganese mixture.
The EL Device has two electrodes – Glass electrode and Back electrode. The glass electrode is the front transparent electrode which is coated with Indium Oxide or Tin Oxide. The Back electrode is coated with a reflective material. In between the glass and back electrodes, the semiconductor material is present.
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