Electroluminescent

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

In contrast to the LEDs, electroluminescent phosphors operate under high voltage and very high electric fields. The Sharp devices are ac and purely... 

A light-emitting diode (LED) is a forward-biasedp—n junction in which the appHed bias enables the recombination of electrons and holes at the junction, resulting in the emission of photons. This type of light emission resulting from the injection of charged carriers is referred to as electroluminescence. A direct band gap semiconductor is optimal for efficient light emission and thus the majority of the compound semiconductors are potential candidates for efficient LEDs. 

Other sohd-state apphcations of sihcon carbide include its use as an electroluminescent diode for use in sound recording equipment and photomultipliers and controllers. It has been studied as a reflective surface for lasers. By combining its excellent thermal conductivity and high electrical resistance, sihcon carbide has also found apphcation as an insulating material for integrated circuit substrates. 

Donor and acceptor levels are the active centers in most phosphors, as in zinc sulfide [1314-98-3] ZnS, containing an activator such as Cu and various co-activators. Phosphors are coated onto the inside of fluorescent lamps to convert the intense ultraviolet and blue from the mercury emissions into lower energy light to provide a color balance closer to daylight as in Figure 11. Phosphors can also be stimulated directly by electricity as in the Destriau effect in electroluminescent panels and by an electron beam as in the cathodoluminescence used in television and cathode ray display tubes and in (usually blue) vacuum-fluorescence alphanumeric 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). 

Benchtop X-ray energy dispersive analyzer BRA-17-02 based on a gas-filled electroluminescent detector with an x-ray tube excitation and range of the elements to be determined from K (Z=19) to U (Z=92) an electroluminescent detector ensures two times better resolution compared with traditional proportional counters and possesses 20 times greater x-ray efficiency compared with semiconductor detectors. The device is used usually for grits concentration determination when analysing of aviation oils (certified analysis procedures are available) and in mining industry. 

The results of simulation have been confirmed by determination of Fe traces in quai tz sand, Cu and Mo in flotation tails and Ag in waste fixing waters on BRA-17-02 analyzer based on X-ray gas-filled electroluminescent detector and on BRA-18 analyzer based on Si-drift detector. The results of the simulation conform satisfactory with the experimental data in the mentioned cases the optimum filtration results in 2 to 5 times lowering of the detection limit. 

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

Another recently discovered form of epitaxy is graphoepitaxy (Geis et al. 1979). Here a non-crystalline substrate (often the heat-resistant polymer polyi-mide, with or without a very thin metallic coating) is scored with grooves or pyramidal depressions the crystalline film deposited on such a substrate can have a sharp texture induced by the geometrical patterns. More recently, this has been tried out as an inexpensive way (because there is no need for a monocrystalline substrate) of preparing oriented ZnS films for electroluminescent devices (Kanata et al. 1988). 

The use of 1 l//-pyrido[2,l-Z)]quinazolin-l 1-ones in an organic electroluminescent device was patented (99JAP(K)99/74080). 2//-Pyrimido[2,l-n]isoquinolin-7-ols were patented as multi-functional fuel and lube additives (97USP5646098). 

Ordered dialkoxy PPV derivative has been prepared by Yoshino et al. [491. oly(2 -nonoyloxy-1,4-phenylene vinylene) 27a forms a nematic liquid-crystalline phase upon melting. The material retains its order upon cooling to room temperature, and its band gap (2.08 eV) is measurably smaller than in an unoricnted sample. Oriented electroluminescence may be achieved by rubbing a thin fdin of the material to induce molecular orientation [50],... 

The synthesis-driven approach towards material science can be applied to create oligomers and polymers with optimized properties, e.g. maximized carrier mobilities and electrical conductivities or high photo- and electroluminescence quantum yields. It becomes obvious, however, that the ability to synthesize structurally defined -architectures is the key to these high performance materials. 

Experiments on transport, injection, electroluminescence, and fluorescence probe the spatial correlation within the film, therefore we expect that their response will be sensitive to the self-affinity of the film. This approach, which we proved useful in the analysis of AFM data of conjugated molecular thin films grown in high vacuum, has never been applied to optical and electrical techniques on these systems and might be an interesting route to explore. We have started to assess the influence of different spatial correlations in thin films on the optical and the electro-optical properties, as it will be described in the next section. 

Figure 6-23. Sketch of the experimental arrangement tor measuring the angular dependence or lluores-ccncc and electroluminescence. The viewing angle 0 is varied between -90 " and +90 .

Figure 9-12. Absorption (Abs), photoluminescence excitation spectrum (PLCX), pholo-lumincscence (PL), and electroluminescence (EL) emission of mLPPP.

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