High field electroluminescence

At the moment it is difficult to see how a considerable improvement in high-field electroluminescence efficiency can be obtained. 

As was the case in Fig. 2.37, PFB exciton electroluminescence is seen at high fields. Because ofthe high noise level, the 10.7-V curve has been truncated below 530 nm. 

The electroluminescence (EL) process is defined as light generation by an application of an electric field. Two types of EL behavior can be distinguished according to the voltage applied low-field EL, called direct current electroluminescence (DC EL), and high-field EL, called alternating current electroluminescence (AC EL) [19]. 

Luminescent emission can be excited by light (photoluminescence), by cathode rays, electric field (electroluminescence), and high temperature (candolumin-escence). 

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

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). 

The enormous progress in the field of electroluminescent conjugated polymers has led to performances of oiganic light-emitting devices (LEDs) that are comparable and in some aspects superior to their inorganic counterparts 11). Quantum efficiencies in excess of 5% have been demonstrated [2] and show that a high fraction of the injected carriers in a polymeric electroluminescence (EL) device form electronic excitations which recombine radiatively. 

Taking advantage of these characteristics, Corma and coworkers (Atienzar et al., 2004) have described and validated an automatic system for high-throughput (HT) characterization of large libraries of solid materials by PL in the range of 350 800 nm. The system proposed is able to provide time-resolved transient emission spectra in the microsecond range and can be employed to characterize materials, particularly in the fields of catalysis and electroluminescence. 

Electroluminescence (EL) studies done on CVP Polyazomethines indicated that it is primarily an electron transport polymer with a turn-on field -105 V/cm. This turn-on field is much better than that reported for solution processed PPV LEDs, and is in the same range as the some of the best values reported for the CVP-PPV. However, EL emission was only observed when a hole-transporting layer was introduced. They suggested that this might be due to the high ITO/polyazomethine energy barrier which injection of holes from the ITO electrode. ... 

---