What is Electroluminescence(EL)
Electroluminescence (EL) is luminescence produced by high energy generated from electrons which are accelerated within phosphors when an alternating current is applied to a luminous layer consisting of phosphor powder.
EL element is largely divided into two types; dispersion-type EL with luminous layer consisting of phosphors and thin film-type EL consisting of dense thin films. Each EL is also subdivided into alternating current type and direct current type according to driving method.
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).
Examples of electroluminescent materials
Electroluminescent devices can be fabricated using thin films of either organic or inorganic materials. The thin film layers contain a bulk semiconductor (or host material for organic EL) and a dopant which defines the visible color emitted. The semiconductor needs to have wide enough bandwidth to allow exit of the light.
The most typical inorganic thin-film EL (TFEL), for example, is ZnS:Mn with its yellow-orange emission. Examples of the range of EL material include:
- Powder zinc sulfide doped with copper or silver
- Thin film zinc sulfide doped with manganese
- Natural blue diamond ( diamond with boron as a dopant ).
- III-V semiconductors – such as InP, GaAs ,and GaN .
- Inorganic semiconductors – such as [Ru(bpy) 3 ] 2+ (PF 6 – ) 2 , where bpy is 2,2′-bipyridine
