Color conversion technique

An efficient internal color-conversion technique will only occur if the polymers in the blend are only weakly phase separated. Otherwise, the various polymers in the blend behave similar to independent parallel diodes and hence a strongly voltage-dependent emission color will be observed.131,137... 

The highly efficient EL devices based on parahexa-phenyl (PHP) [52] are very suitable for the latter color conversion technique because their emission is deep... 

Applying this color conversion technique, emission colors (e.g., green, yellow, orange, magenta, and red) throughout the whole visible range can be obtained by covering the PHP EL devices with dye layers of different concentrations and, if necessary, suitable filters. 

Blue Large-Area EL Devices Covered with Filters and Appropriate Dye Layers That Convert the Blue EL Emission into the Required Emission Color. One of the most promising methods for the production of flat color screens is the use of blue PLEDs covered with dye layers to convert the EL emission into the RGB colors and, if necessary, with filters to purify the emission light [171-174] (see Fig. 30.20). In principle, the internal quantum efficiency of this technique for color conversion from blue into any other emission color can approach 100%. 

Colorimetry. A variety of colorimetric techniques have been used to measure ions such as NH4, SO4-, and NO7 in ambient particles. For example, nitrate can be measured by reduction to nitrite using hydrazine in the presence of a copper catalyst, followed by its conversion to a colored azo dye, which can be measured by its absorbance at 524 nm (Mullin and Riley, 1955). Sulfate has been determined using an exchange reaction between sulfate and a barium-nitrosulfo-nazo(III) chelate in aqueous acetonitrile the chelate has an absorbance peak at 642 nm and hence the decrease in this peak can be followed as a measure of the amount of sulfate present that has exchanged with the chelate (Hoffer et al., 1979). Similarly, NH4 can be measured by the indophenol blue method (Weather-burn, 1967). 

The simplest, but least accurate, method of assaying DPO activity is to record the final color yield when the enzyme is incubated with a suitable chromogenic substrate such as catechol, DOPA, or 4-methylcatechol. DOPA is the most frequently used substrate in colorimetric assays because it yields a dark brown/black end-product. In this reaction, catecholase catalyzes the conversion of DOPA to dopaquinone and then to the red dopachrome, which subsequently polymerizes to yield dark brown melanin-type pigments. Unfortunately, this simple procedure has serious limitations, as it measures the end-product of a sequence of reactions rather than the true initial reaction rate. Furthermore, because different substrates yield different final colors, valid kinetic comparisons between substrates are not possible. Nevertheless, this simple assay technique has proved adequate for useful comparative studies of the levels of enzymic browning in different fruit varieties and similar problems (Vamos-Vigyazo, 1981 Machiex et al., 1990). 

Techniques. In 1962, McKinley and Read (42) developed an esterase-inhibition technique for the detection of organophosphate pesticide residues on paper chromatograms. The procedure involved conversion of the thiophosphates with bromine to yield active esterase inhibitors, the inhibition by the pesticide of the esterases from a beef liver homogenate sprayed onto the chromatogram, the hydrolysis of the substrate (a-naph-thyl acetate) which was sprayed onto the paper after the liver homogenate had dried, and the development of a background color between Fast Blue RR and the hydrolysis product, a-naphthol. 

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