The basic electro-luminescent (EL) display is a sandwich consisting of an upper and a lower electrode sandwiching a material which gives off light when excited by high frequency.
There are several different types of EL display which conform to this basic design and they fall into several groups. One group is known as “High-Field” EL because they create light by using an electric field to excite phosphors with high-energy electrons. These electrons collide with atoms in the phosphors, knocking electrons out of orbit around the atoms’ nucleii (the atoms are ionised). The electrons then snap back into orbit around an atom’s nucleus and, as they do so, generate light. This principle of exciting phosphors to produce light is similar to a CRT. In a CRT, however, an accelerated electron beam is used to excite the phosphors; in a high-field EL, the electrons are excited by the high frequency field.
The high-field ELs can themselves be sub-divided into those using direct current (DC EL) and those using alternating current (AC EL). The DC ELs and some of the AC ELs are only suitable for use in low information content displays, such as car instrument panels, but several types of AC ELs are being developed for use in full-colour, high-resolution displays. For example: Planar has developed very small (less than an inch diagonally), thin-film devices for use in head-mounted displays while Westaim has used a thick-film, screen-printing technique to produce an EL it calls the Solid State Display with a 17″ diagonal. The Westaim 17″ SSD is still a prototype at the moment but the company plans a series of products of between 25″ and 42″ for use in wall-mounted HDTVs.
Update: Westaim’s EL scheme is still at the prototype and sample production stage in July 2006 although the EL activity is now being run under the name of iFire