Sensitization quantum efficiencies

Standardizing the Method Equations 10.32 and 10.33 show that the intensity of fluorescent or phosphorescent emission is proportional to the concentration of the photoluminescent species, provided that the absorbance of radiation from the excitation source (A = ebC) is less than approximately 0.01. Quantitative methods are usually standardized using a set of external standards. Calibration curves are linear over as much as four to six orders of magnitude for fluorescence and two to four orders of magnitude for phosphorescence. Calibration curves become nonlinear for high concentrations of the photoluminescent species at which the intensity of emission is given by equation 10.31. Nonlinearity also may be observed at low concentrations due to the presence of fluorescent or phosphorescent contaminants. As discussed earlier, the quantum efficiency for emission is sensitive to temperature and sample matrix, both of which must be controlled if external standards are to be used. In addition, emission intensity depends on the molar absorptivity of the photoluminescent species, which is sensitive to the sample matrix. 

HgCdTe photodiode performance for the most part depends on high quantum efficiency and low dark current density (83,84) as expressed by equations 23 and 25. Typical values of at 77 K ate shown as a function of cutoff wavelength in Figure 16 (70). HgCdTe diodes sensitive out to a wavelength of 10.5 p.m have shown ideal diffusion current limitation down to 50 K. Values of have exceeded 1 x 10 . Spectral sensitivities for... 

Some of these devices have a respectable quantum efficiency of charge generation and collection, approaching 0.4 (20). The nature of the polymeric binder has a large effect on the device performance (21), and so does the quaUty and source of the dye (22). Sensitivity to the environment and fabrication methods results in some irreproducibiUties and batch-to-batch variances. However, the main advantage of the ZnO-based photoreceptor paper is its very low cost. 

The RCA C313034 with a GaAs cathode has a cathode quantum efficiency far better than that of the S-20 type in the red region. This photomultiplier tube allows the study of the 2700-3200 cm-1 Raman shift region with greater sensitivity using the red line (Fig. 8). 

Quantum efficiency (QE) - The sensitivity of a detector can be nearly perfect, with up to 99% of the photons detected at the wavelength for which the detector is optimized. 

Between 1923 and 1927, the concepts of quantum efficiency (number of photons emitted divided by number of photons absorbed by a sample) and quantum yield (fraction of excited molecules that emit) had been defined and values determined for many compounds by Vavilov (34). The quantum yield indicates the extent that other energy loss mechanisms compete with emission in an excited molecule. Although the quantum yield is influenced by the molecular environment of the emitter, for a given environment it depends on the nature of the emitting compound and is independent of concentration and excitation wavelength, at least at low concentrations (35). Tlius, it serves as another measurable parameter that can be used to identify the compounds in a sample and also, because of its sensitivity to the surroundings of the luminophore, to probe the environment of the emitter. 

In sensitization studies, the 7 state of anthrabarrelene (45) proved to be totally unreactive. However, direct photolysis of 2,3-anthrabarrelene afforded 2,3-anthrasemibullvalene via vinyl-vinyl bridging with a quantum efficiency of 0.25 ... 

The incident monochromatic photon-to-current conversion efficiency (IPCE), also called external quantum efficiency, is defined as the number of electrons generated by light in the external circuit divided by the number of incident photons as a function of excitation wavelength. It is expressed in Equation (7).29 In most cases, the photoaction spectrum overlaps with the absorption spectrum of the sensitizer adsorbed on the semiconductor surface. A high IPCE is a prerequisite for high-power photovoltaic applications, which depends on the sensitizer photon absorption, excited state electron injection, and electron transport to the terminals ... 

Very promising indeed is the ternary compound AlGaN. By shifting the Al/Ga ratio its spectral sensitivity can be tailored. The cut-off wavelength can be shifted between 380 nm and 310 nm [3]. Quantum efficiencies up to 50% have been obtained for SiC as well as for GaN, which is similar to the UV sensitivity of UV-en-hanced Si photodiodes. 

Polycrystalline GaN UV detectors have been realized with 15% quantum efficiency [4], This is about 1 /4 of the quantum efficiency obtained by crystalline devices. Available at a fixed price, however, their increased detection range may well compensate their lack in sensitivity. Furthermore, new semiconductor materials with a matching band gap appear as promising candidates for UV detection if the presumption of the crystallinity is given up. Titanium dioxide, zinc sulfide and zinc oxide have to be mentioned. The opto-electronic properties and also low-cost production processes for these compound semiconductors have already been investigated to some extent for solar cell applications [5]. 

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