Broad band matching

Colorimeters. Also known as tristimulus colorimeters, these are instniments that do not measure spectral data but typically use four broad-band filters to approximate the jy, and the two peaks of the x color-matching functions of the standard observer curves of Figure 7. They may have lower accuracy and be less expensive, but they can serve adequately for most industrial color control functions. Examples of colorimeters are the BYK-Gardner Co. XL-835 the Hunter Lab D25 series the Minolta CA, CL, CS, CT, and CR series (the last of these is portable with an interface) and the portable X-Rite 918. 

Interferences in atomic absorption measurements can arise from spectral, chemical and physical sources. Spectral interference resulting from the overlap of absorption lines is rare because of the simplicity of the absorption spectrum and the sharpness of the lines. However, broad band absorption by molecular species can lead to significant background interference. Correction for this may be made by matrix matching of samples and standards, or by use of a standard addition method (p. 30 et seq.). 

When electromagnetic radiation passes through transparent matter, some of it is absorbed. Strong absorption will occur if there is a close match between the frequency of the radiation and the energy of one of the possible electronic or molecular absorption processes characteristic of the medium. A plot of absorbance (A) against wavelength (X) or frequency (v) for a particular material is termed an absorption spectrum. The complexity of the absorption spectrum depends on whether atomic (simple, with a few sharp absorption bands) or molecular (complex, with many broad bands) processes are responsible. 

While the first factor in these expressions varies, the proportionality with respect to the acquisition field is always present. In order to maximize SjN, it is therefore advantageous to use always the largest possible acquisition field Ba and make the acquisition frequency match the corresponding Larmor frequency jBa of the measured nuclide. This, however, can be done only when using a broad-band console. 

We illustrate this principle with the phosphor spectra shown in Figure 5, taken from ref ( ). The Mn + activated phosphate, a broad band emitter, was the original red color TV phosphor. It was superseded in 1960 when RCA introduced the all sulfide screen utilizing (Zn,Cd)S Ag as the red primary. The spectrum of the sulfide is also broad and actually makes an even poorer match to the eye than that of the phosphate, but this is more than compensated for by a threefold increase in efficiency (integrated area under the curve). The spectrum of YV0 Eu ", which was introduced as a color TV phosphor in 1964 by Sylvania as a result of pioneering work by Levine and Palilla ( ), is qualitatively different and beautifully illustrates the eye response principle. 

Figure 141 shows the EL spectra from a microcavity (a) and conventional LED (b) based on the emission from an NSD dye forming a thin emitting layer of a three-organic layer device. It is apparent that the half-width of emission spectra from the diode with microcavity is much narrower than those from the diode without cavity. With 0 = 0°, for example, the half-width of the spectrum of the diode with cavity is 24 nm whereas that of the sample without cavity increases to 65 nm. According to Eq. (275), the resonance wavelength, A, decreases with an increase of 0 in agreement with the experimental data of Fig. 141. We note that no unique resonance condition in the planar microcavity is given due to broad-band emission spectrum of the NSD emission layer. Multiple matching of cavity modes with emission wavelengths occurs. Thus, a band emission is observed instead a sharp emission pattern from the microcavity structure as would appear when observed with a monochromator the total polychromic emission pattern is a superposition of a range of monochromatic emission patterns. The EL spectra...

Figure 9.14. Brillouin spectrometer using fibre optics to increase the signal-to-noise ratio. (1) Light source consisting of a master laser (1a) a slave with matched frequency (1b) and control unit (1c) for sensitive stabilization of the difference frequency Sv. (2) Signal splitter. (3) Fibre coupler. (4) Polarizer. (5) Chopper. (6) Lens. (7) Cuvette placed on a goniometer. (8) Termination. (9) Slit. (10) Broad-band (10 GHz) APD. (11) Photodiode with a smaller bandwidth (1 GHz). (12) Spectrum analyser (10 GHz) for controlling the intermediate frequency Sv. (13) Spectrum analyser (1 GHz) for the measurement of the half-power bandwidth, Av, of the Brillouin peak. (14) Amplifier system. (15) Process control computer. (Reproduced with permission of Elsevier, Ref [96].)...

Because the metal electrodes make ohmic contacts with the p- and n-doped regions, both electrons and holes can be efficiently injected and the carrier densities are approximately balanced. Thus, higher quantum efficiencies are often observed in LECs than in LEDs made with the same semiconducting polymer. Moreover, the same stable electrodes can be used with any semiconducting polymer. By contrast, recall that for polymer LEDs, the anode and cathode metals must be matched to the rr- and Tr -bands, respectively. Thus, for polymer LEDs, different electrodes must be developed to optimize emission from each new polymer (and for each new color ). Red, green and blue (and broad-band white) emission from polymer LECs have been demonstrated with external efficiencies of 2-4% using air stable electrodes (aluminum). 

Synthetic polyalphaolefins are composed of a very limited number of branched alkane isomers, all having approximately the same molecular weight and also completely wax-free. The wax isomerisation product has a wider spread of isomers and covers a broad band of different molecular weights. It also contains some wax and these products cannot match the low-temperature properties of the polyalphaolefins. 

It should also be noted that the effective activation spectrum of photosensitizers is not necessarily exactly the same as their absorption spectrum in solution. The peak wavelengths may be shifted by several nanometers, due to binding of the photosensitizer to biomolecules (e.g. proteins). If a narrow wavelength source (e.g. laser) is used, it is important to match the wavelength to the true in vivo activation peak, so this needs to be determined, typically by studies in animal models. With broad-band sources (LEDs, lamps), this is less critical. 

Figure 3. Illustration of the overlap between a photosensitizer absorption (activation) peak and a broad-band light source. The product of power and absorption is calculated at each wavelength and then summed over all wavelengths (equation 1) to obtain the effective power of the source for this photosensitizer. Also indicated is a laser source at a wavelength matching the photosensitizer peak.

Fig. 2.7 To obtain a iow RCS over a broad band an antenna ideaiiy shouid have (a) as tow a residuai scattering as possibie (i.e., C 0) and (b) a broadband match yietding r 0.

The excitation and emission spectra of the Ba3Sc409 Ce phosphor are shown in Fig. 7.16. The excitation spectrum consisted of a broad band covering die region from near-UV to visible light, which is a good match with the emission band of... 

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