Displays electroluminescent

The current interest in exploring the semiconducting properties of conducting polymers is for application to electroluminescence, i.e., using these materials as an emissive layer in LEDs [125, 206-211], 

Electroluminescence is the emission of light by electrical excitation. Pope and co-workers [212] observed emission in single crystals of anthracene using silver paste electrodes at 400 V. Subsequently, it was established that the phenomenon of electroluminescence necessitates the injection of electrons from one electrode and holes from the other, the capture of one by the other (recombination) and the radioactive decay of the excited state (exciton) produced by the recombination process. 

Current flat-panel display technology primarily revolves aroimd inorganic LEDs, backlit liquid crystal displays (LCDs) and vacuum fluorescent displays. Although these technologies are trim and efficient compared with cathode ray tubes, they can be bulkier and much more power consuming than required for many applications. In many battery-operated devices, such as laptop computers, cellular telephones and other hand-held instruments, the illuminated display is the primary energy consumer. Furthermore, LED displays are expensive to fabricate because of the many individual diodes required to make up an alphabet, each with its own contacts and interconnections. These problems forced researchers to look for other materials. 

Owing to the above advantages, a number of conducting polymers have been produced that emit light across the visible spectrum and which may be used to fabricate devices with greater quantum efficiencies [31, 213-215]. 

Polymer Wavelength (nm) / Colour Repeating Unit Year 

---

Other glass-ceramics may find potential use in Hquid crystal and electroluminescent displays. 

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

Commonly used II-VI compounds include zinc sulfide, zinc selenide, zinc telluride, cadmium sulfide, cadmium telluride, and mercury cadmium telluride. These materials are not as widely used as the III-V compounds, one reason being that it is difficult to achieve p-type doping. Mercury cadmium telluride is used extensively in military night sights, which detect in the 8-13 im spectral band (a similar material, platinum silicide, is being developed for that purpose). The major applications ofCVD II-VI compounds are found in photovoltaic and electroluminescent displays. 

Growth and characterization of electroluminescent display devices using vacuum-deposited organic materials... 

A.N. Krasnov, ELDs rise on organic wings electroluminescent-display technology is being rescued from its industrial niche by implementations using organic materials, Inf. Display, 18 18-21, 2002. 

C Hosokawa, M Eida, M Matsuura, K Fukuoka, H Nakamura, and T Kusumoto, Organic multicolor electroluminescence display with fine pixels, Synth. Met., 91 3-7, 1997. 

AB Chwang, MA Rothman, SY Mao, RH Hewitt, MS Weaver, JA Silvernail, K Rajan, M Hack, JJ Brown, X Chu, L Moro, T Rrajewski, and N Rutherford, Thin Film Encapsulated Flexible Organic Electroluminescent Displays, Proceedings of the Society for Information Display, Digest of Technical Papers, Vol. 34(2), Baltimore, 2003, pp. 868-871. 

Polythiophene derivatives are being used in FETs. Polypyrrole is being used as microwaveabsorbing stealth screen coatings and in sensing devices. PPV derivatives are being used in the production of electroluminescent displays. 

The use of luminescent materials, the subject of Chapter 3, which was at one time confined largely to the production of fluorescent lamps and cathode ray tubes has spread further into everyday life. It is a common sight to see phosphorescent safety signage in low-light environments, to wear fluorescent garments, to look at electroluminescent displays and to use light emitting diodes in trafhc control and vehicle... 

In displays ZnO powders are used as green phosphors [169]. Recently, magnetron sputtered films of ZnO-based compounds, for instance Zn2SiO/ Mn or ZnGa204 Mn were used as green phosphors in thin-film electroluminescence displays [170,171]. Even white cathodoluminescence was observed for self-assembled ZnO micropatterns [172]. 

In past decades, lanthanide complexes (except Pm, Sc, and Ce complexes) and related electroluminescent devices have been studied extensively. In this section we describe recent progress in lanthanide complex-based luminophores, especially for Eu and Tb complexes, which are being developed for improving the color properties of electroluminescent displays. 

Atomic layer deposition is an established technique for the production of large-area electroluminescent displays, and is a likely future method for the production of the very thin films needed in microelectronics. However, many other potential applications of ALD are discouraged by its low deposition rate, typically less than 0.2 nm (less than half a monolayer) per cycle. For silica deposition, completing a cycle of reactions typically requires more than 1... 

---