Color emitters

In general, color emitters used as components of pyrolants are metallic compounds rather than metal particles. Metal particles agglomerate to form liquid metal droplets and liberation of metal atoms in flames occurs only at the surface of the droplets. On the other hand, metallic compounds decompose at relahvely low temperatures compared with metal particles and liberate dispersed metal atoms. Table 12.5 shows typical salts used to obtain emissions of the requisite colors. 

Table 12.5 Chemical compounds used as color emitters.

Eluorescent lamps for showing plants use a blue-white phosphor blended with a deep red-emitting phosphor. This more closely corresponds to the action spectmm for plant growth because there is Htfle green in the spectmm, African violets, for example, have leaves which appear more purple in color. The deep red emitter which is commonly used is magnesium fluorogermanate activated by Mn. ... 

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 fluorescence color converter technique [32] can, in principle, overcome much of this power loss by replacing the white light emitter with a blue-emitting organic stack, and the absorbing filters with green and red fluorescent dyes. Thus when a green pixel is desired, the OLED underneath is turned on and the blui... 

Electron-Deficient Polymers - Luminescent Transport Layers 16 Other Electron-Deficient PPV Derivatives 19 Electron-Deficient Aromatic Systems 19 Full Color Displays - The Search for Blue Emitters 21 Isolated Chromophores - Towards Blue Emission 21 Comb Polymers with Chromophores on the Side-Chain 22 Chiral PPV - Polarized Emission 23 Poly(thienylene vinylene)s —... 

Full Color Displays - The Search for Blue Emitters... 

However, the method will not enhance the external quantum yield of the LED, moreover, proper optical coupling between the layers has to be achieved in order not to decrease the QY loo much [61. One of the obvious problems is the principal requirement of having the ITO-covered glass substrate between the color converter and the cmitLer layer. This can also lead to color bleeding, an effect where the emitter layer excites not only the conversion layer, it is supposed to address but also neighboring ones. 

Fluorescent small molecules are used as dopants in either electron- or hole-transporting binders. These emitters are selected for their high photoluminescent quantum efficiency and for the color of their emission. Typical examples include perylene and its derivatives 44], quinacridones [45, penlaphenylcyclopenlcne [46], dicyanomethylene pyrans [47, 48], and rubrene [3(3, 49]. The emissive dopant is chosen to have a lower excited state energy than the host, such that if an exciton forms on a host molecule it will spontaneously transfer to the dopant. Relatively small concentrations of dopant are used, typically in the order of 1%, in order to avoid concentration quenching of their luminescence. 

Because luciferyl adenylate emitted a red chemiluminescence in the presence of base, coinciding with the red fluorescence of 5,5-dimethyloxylucferin, the keto-form monoanion Cl in its excited state is considered to be the emitter of the red light. Thus, the emitter of the yellow-green light is probably the enol-form dianion C2 in its excited state, provided that the enolization takes place within the life-time of the excited state. Although the evidence had not been conclusive, especially on the chemical structures of the light emitters that emit two different colors, the mechanism shown in Fig. 1.12 was widely believed and cited until about 1990. 

According to Branchini et al. (2004), luciferase modulates the emission color by controlling the resonance-based charge delocalization of the anionic keto-form of oxyluciferin in the excited state. They proposed the structure C5 as the yellow-green light emitter, and the structure C6 as the red light emitter. 

Firefly bioluminescence, 3-19 characteristics, 12 color of luminescence, 12 effect of pH, 13 effect of temperature, 14 factors required, 3, 4 light emitter, 17-19 mechanism, 15-17 overall reaction, 5... 

A system for emittance color matching is given in the following ... 

If we have a certain color, a change in intensity has a major effect on what we see (in both reflectance and emittance). For example, if we have a blue, at low intensity we see a bluish-black, while at high intensity we see a bluish-white. Yet, the hue has not changed, only the intensity. This effect is particularly significant in reflectance since we can have a "light-blue" and a "dark-blue", without a change in chromaticity coordinates. 

P-22 ZnS Ag+ + ZnCdS2 Ag+ + Y202S Eu3+ Mix of phosphors, each phosphor prepared and applied separately. ZnS, (Zno.88-Ago.i2)S2> MgCl2 LiS04 ZnS, (Zn0.715.Ag0.285)S2, CdS MgCl2.NaCl Y203 Euo.65 S Color television (blue, green, and red emitters)... 

Fig. 6.4. Statistical confidence level associated with the electric events synchronized with the laser pulses during a thunderstorm. The color scale is transparent below 98% (i.e., for error risks above 2%), leaving the topographical background uncovered. Arrowhead location of the laser-induced plasma channel Arrow tail laser emitter. Topographic background courtesy of US Geological Survey [31]...

---