Electron electroluminescence

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. 

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 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. 

Thin Films of Electroluminescent Polymers 335 Electronic Eneigy Structure 336 Optical Properties 336 Electrical Transport Properties 338... 

This chapter is organized as follows in Section 11.2 the relevant properties of electroluminescent polymer Films are summarized in Section 11.3 the electronic properties of mctal/polymer junctions are described in Section 11.4 single layer polymer LEDs are discussed in Section 11.5 multi-layer polymer LEDs are considered and Section 11.6 summarizes the conclusions. 

Structural binder A wide range of applications in electronics makes use of the plastics as a structural binder to hold active materials. For example, a plastic such as polyvinylidene fluoride is filled with an electroluminescent phosphor to form the dielectric element in electroluminescent lamps. Plastics are loaded with barium titanate and other high dielectric powders to make slugs for high K capacitors. The cores in high frequency transformers are made using iron and iron oxide powders bonded with a plastic and molded to form the magnetic core. 

Electrical industries, polyimides in, 269 Electroluminescent devices, 271 Electronic applications, 26 polyimide, 269... 

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