Electroluminescent phosphors

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

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. 

Within the limitations on the physical properties which generally restrict plastics to low precision optics, plastics materials have found wide applications in optical products that range from lights to binders for electroluminescent phosphors to fiber optics and lasers. They represent an easily worked material with a wide range of desirable optical properties in simple to complex shapes. In this review the discussion has been limited to the differences between plastics and optical glass materials and to some of the unique design possibilities that are especially important for plastics. Using the optical arts and the... 

Figure 4.S7. SEM images of an electroluminescent phosphor particle, ZnS (used in backhght displays for cell phones, watches, etc.), before (a) and after (b) the deposition of an aluminum oxide thin film. This film is a transparent coating that prevents the phosphor particle from undergoing humidity-accelerated decay. A technique known asfluidized-bed CVD was used, where a carrier gas both delivered the precursors to a vertically aligned CVD chamber, and dispersed the powdery sample in order to expose all surface regions to the precursor vapors.

A patent is issued for the Indiglo nightlight, consisting of electroluminescent phosphor particles High-definition television is invented... 

Sawada, M., Oobayashi, S., Yamaguchi, K., Takemura, H., Nakamura, M., Momose, K., and Saka, H., Characteristics of light emission lifetime of electroluminescent phosphor encapsulated by titanium-silicon-oxide film, Jpn. J. Appl. Phys., 41, 3885, 2002. 

Electroluminescent phosphor paste, 125 Luxprint 7153E Barium titanate paste, 125 Lynite ... 

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. 

It is worth summarizing at this point the different excitation methods used for phosphors that will be referred to throughout this chapter. There are three types photoluminescence (PL) which is based on initial excitation by absorption of light, cathodoluminescence (CL) which is based on bombardment with a beam of electrons, as in a cathode ray tube (CRT) and electroluminescence (EL) which is based on application of an electric field (either a.c. or d.c.) across the phosphor. 

Efficient IR-emitting phosphors excited by a direct current electroluminescence (DCEL) device were first reported in 1969. Sixty/40 CdS/ZnS doped with 10-4gg-1 Cu was shown to be an efficient converting phosphor giving a maximum output at 900nm.20 The near-IR emission of thin-film electroluminescence (TFEL) devices containing ZnS Er (at 980 nm), ZnS Nd (at 900 nm), and ZnS Tm (at 805 nm) have been reported.21... 

It is worth noting some historical aspects in relation to the instrumentation for observing phosphorescence. Harvey describes in his book that pinhole and the prism setup from Newton were used by Zanotti (1748) and Dessaignes (1811) to study inorganic phosphors, and by Priestley (1767) for the observation of electroluminescence [3], None of them were capable of obtaining a spectrum utilizing Newton s apparatus that is, improved instrumentation was required for further spectroscopic developments. Of practical use for the observation of luminescence were the spectroscopes from Willaston (1802) and Frauenhofer (1814) [13]. 

Red phosphors are formed either by heating white phosphorus or by exposing white phosphorus to sunlight. It is quite different from the explosive white phosphorus. For instance, when scratched on a surface, the heads of safety matches made of red phosphorus convert back to white phosphorus and ignite due to the heat of the shght friction of the match on a rough surface. Red phosphorus is also used in fireworks, smoke bombs, and pesticides and to make phosphoric acid, electroluminescent paints, and fertilizers. 

Strontium thiogallate SrGa S iCe, doped with 4 mol% of cerium, gives a very good blue phosphor 455 nm), which has found to be useful in thin-film electroluminescent devices (see section 3.8.3.2). 

CdTe is used in infrared optics (41), phosphors, electroluminescent devices, photocells, and as a detector for nuclear radiation (42). 

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]. 

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