Function of excitation wavelength

Fig. 8. Low-temperature (20 K) resonance Raman spectra of oxidized P. furiosus 3Fe Fd as a function of excitation wavelength (191).

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 ... 

The E,Z-photoisomerization of previtamin D to tachysterol has also received recent attention. Jacobs and coworkers examined the process in various solvents at 92 K and found evidence for the formation of a triene intermediate which converts thermally (Ea ca 6.5 kcal mol 1) to the more stable tEc rotamer of tachysterol (tEc-T equation 58)230. The rate of this conversion is viscosity dependent. They identified this intermediate as the cEc rotamer, produced by selective excitation of the cZc rotamer of previtamin D. In a re-examination of the low temperature ,Z-photoisomerization of previtamin D as a function of excitation wavelength, Fuss and coworkers have suggested an alternative mechanism, in which tEc-1 is produced directly from cZc-P and cEc-T directly from tZc-P (equation 59)103. This mechanism involves isomerization about both the central double bond and one of its associated single bonds—the hula-twist mechanism of Liu and Browne101 — and involves a smaller volume change than the conventional mechanism for ,Z-isomerization. The vitamin D system has also been the subject of recent theoretical study by Bemardi, Robb and Olivucci and their co workers232. 

The threshold wavelength of incident photons to produce the electronically excited Na(2P) is 2440 A. The quenching cross sections by H2. HC1, C02, and H20 for the sodium D lines have been measured as a function of exciting wavelength above 500"C. The quenching cross sections by HCI and C 02 decrease with an increase of relative velocities between the excited Na atoms and quenching molecules [Hanson (441), Earl et al. (332, 333)]. 

The incident monochromatic photon-to-current conversion efficiency (IPCE) is plotted as a function of excitation wavelength. The IPCE value in the plateau region is 80% for complex 2, while for complex 25 it is only about 66%. In the red region, the difference is even more pronounced. Thus, at 700 nm the IPCE value is twice as high for the fully protonated complex 2 as compared to the deprotonated complex 25. As a consequence, the short circuit photocurrent is 18-19 mAcrn-2 for complex 2, while it is only about 12-13 mA cm-2 for complex 25. However, there is a trade-off in photovoltage, which is 0.9 V for complex 25, as compared to 0.65 V for complex 2. Nevertheless, this is insufficient to compensate for the current loss. Hence, the... 

Table 3 Quantum yields of FeNTA disappearance as at pH 4 and 7 (from [62]) a function of excitation wavelength...

Peticolas was the first to measure the UV resonance Raman spectrum and excitation profile (resonance Raman intensity as a function of excitation wavelength) of adenine monophosphate (AMP) [147, 148], The goal of this work, besides demonstrating the utility of UV resonance Raman spectroscopy, was to elucidate the excited electronic states responsible for enhancement of the various Raman vibrations. In this way, a preliminary determination of the excited-state structures and nature of each excited electronic state can be obtained. Although the excited-state structural dynamics could have been determined from this data, that analysis was not performed directly. 

Figure 4.13 Enhancement of quantum dots photoluminescence near a nancqiarticle as a function of excitation wavelength for several single metal nani iarticles. Black dots are the ratio of the photoliuninescence near a nanc article to photoluminescence ir from a nanoparticle. The trace in each spectra is the LSPR...

Excitation spectrum In fluorescence spectroscopy, a plot of fluorescence intensity as a function of excitation wavelength. Exhaustive extraction A cycle in which an organic solvent, after percolation through an aqueous phase containing the solute of interest, is distilled, condensed, and again passed through the aqueous phase. 

We developed two kinds of multidimensional fluorescence spectroscopic systems the time-gated excitation-emission matrix spectroscopic system and the time- and spectrally resolved fluorescence microscopic system. The former acquires the fluorescence intensities as a function of excitation wavelength (Ex), emission wavelength (Em), and delay time (x) after impulsive photoexcitation, while the latter acquires the fluorescence intensities as a function of Em, x, and spatial localization (%-, y-positions). In both methods, efficient acquisition of a whole data set is achieved based on line illumination by the laser beam and detection of the fluorescence image by a 2D image sensor, that is, a charge-coupled device (CCD) camera. 

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