Excitation profile , fluorescence

The fluorescence is generated inside the sample by photons that are already temporally dispersed. After excitation, the fluorescence is scattered backward and forward and diffuses finally to the sample surface. Kinetically, the diffusion process has to be considered as a consecutive reaction step that creates a maximum in the temporal fluorescence intensity profile. 

The tyrosinate fluorescence observed with bovine testes calmodulin is argued to be due to tyrosinate in the ground state.(123) Of the two tyrosine residues in this calmodulin, Tyr-99 apparently has a low pKa near 7 for the formation of tyrosinate, which is most likely due to nearby side chains that are involved in calcium binding. These groups could then also account for the complex pH dependence of the 345-nm emission intensity. Besides the tyrosine and tyrosinate emissions at 305 and 345 nm, respectively, Pundak and Roche(123) also reported the existence of a third emission band between 312 and 320 nm. This band was similar in its pH and calcium dependence to the other residue, Tyr-138, and was speculated to be a result of a combination of contributions from the tyrosine and tyrosinate emissions. Since this band has its excitation profile shifted to the red, however, it could be that a hydrogen-bonded tyrosine exists in this calmodulin. Alternatively, it has also been found that the presence of the 345-nm emission depends upon the method of preparation (G. Sanyal, personal communication). 

Spectrofluorometry underpins all luminescent techniques for characterizing the target analyte and the associated sample matrix. LIF occurs from the vacuum UV through the NIR range, but is most common between 250 nm and 800 nm. A typical fluorescent profile contains an absorption spectrum and an emission spectrum as depicted in Figure 11.3. Spectrofluorometric excitation profiling at emission maxima and syn-chronons scanning are common methods to characterize a fluorophore. 

The fluorescence of TPHA 3 is not a mirror image of its absorption spectrum and the emission intensity is sensitive to concentrations greater than 10 M. The excitation profile of 3 also varies with concentration, believed to be due to aggregation of TPHA in solution and only emulates the ultraviolet-visible (UV-Vis) spectrum at concentrations less than 10 M. The Aem decreased from 633 nm in toluene to 619 nm in dimethyl sulfoxide (DMSO), and this is thought to be indicative of a polar ground state and nonpolar excited state <1998JA2989>. 

Partial saturation of the HO absorption and use of excitation line widths wider than the HO absorption line width are in general undesirable, because they may produce spurious HO while exciting HO fluorescence with less than 100% efficiency (103). However, the issue is not as simple as matching the HO absorption profile exactly and avoiding all saturation. For instance, a matched laser excitation line width is more difficult to achieve and to keep tuned to the HO absorption, and the... 

Scanning the laser across a sodium transition produces excitation profiles as shown in Fig. 2. Irrespective of whether a one- or two-photon transition was involved, we found the width of the resulting ionization profile to exceed that of the corresponding fluorescence excitation profile. We account for this fact by assuming that the process... 

Figure 2. Simultaneously recorded ionization profile (upper curve,) and fluorescence excitation profile (lower curve,) of the 3S,/2 -3Ps/l transition. Fluorescence...

Saturation Broadening in Flames and Plasmas As Obtained by Fluorescence Excitation Profiles... 

Gaussian Laser Profile-Voigt Atom Profile. This case turns out to be a better approximation of our experimental situation, i.e., the laser FWHM is fairly broad compared to the absorption line width and the absorption profile of atoms in an atmospheric combustion flame is described by a Voigt profile. Here the laser is assumed to have a Gaussian spectral profile as well as a Gaussian atomic absorption profile. In this case, convolution of two Gaussian functions is still a Gaussian function. Evaluation of the ratio n2/nT, and the fluorescence radiance. Bp, allows determination of the half width of the fluorescence excitation profile, 6X... 

COMPARISON BETWEEN THE THEORETICAL AND THE EXPERIMENTAL VALUES OF THE FLUORESCENCE EXCITATION PROFILE HALFWIDTHS FOR THE Ar/02/H2 FLAMES.(a) ... 

Direct Measure- ment Fluorescence "" Excitation Profile Saturation Broadening ... 

Diffuse reflectance spectra (A) of Agg NaX taken during dehydration under vacuum and oxygen treatment (400 torr). Fluorescence emission and excitation profiles (B) corresponding to stage C in Figure 5(A) (15). 

At this point we note that the overall form of the absorption, fluorescence emission and excitation profiles for Agx, Ag + and AgP+ for AgxNaX and AgxNaY is superficially reminiscent of those observed for Ag°, Ag2 0, and Ag3 ° entrapped in rare gas solids (4-10). However, a number of important differences are also apparent. These details are discussed for each silver guest as a necessary prelude to the subject of metal-support interactions. 

The overall orm, but not the detail, of the fluorescence emission and excitation profiles for Ag° atoms in site I of X and Y zeolites is similar to those observed for... 

The details of the mechanism of decay of states in alkanes retain their interest. The effect of deuterium on fluorescence lifetimes has been discussed in terms of the theory of radiationless transitions. Analysis of fluorescence line shapes and Raman excitation profiles of tetradesmethyl-p-carotene in isopentane has been carried out at 190 and 230K . Solvation occurs over a time scale of about 100 fs whilst vibrational relaxation has a time scale of about 250 fs. The kinetics of the interaction of alcohols with the excited state of triethylamine shows involvement of a charge transfer exciplex . Ionizing radiation is a means of exciting saturated hydrocarbons and the complexity of three component systems containing saturated hydrocarbons, aromatic solvent, and fluorescent solute has been examined. ... 

In each carotenoid, the 2A (0-0) energy for the absorptive transition determined by resonance-Raman excitation profile in the crystalline state is in complete agreement with that for the emissive transition determined by fluorescence spectroscopy in n-hexane solution, a fact which strongly suggests that neither the Stokes shift nor the dependence on the polarizabiliry of the environment (in -hexane solution vs. in crystal) is present in this particular electronic state. 

In special cases it can be useful or even required to excite the fluorescence by two-photon absorption [132, 319, 493, 494, 521]. The excitation wavelength may then be entirely outside the spectral sensitivity range of the detector. Moreover, the pulse profile obtained by detecting the laser pulse directly may not correspond to the effective temporal two-photon excitation profile of the sample. A useful way to obtain an IRF in a two-photon system has turned out to be second harmonic generation from a suspension of gold particles [206, 375]. 

The fluorescence lifetime, tf, is determined by observing the decay in fluorescence intensity (decay profile) of a fluorophore after excitation. Immediately after a molecule is excited the fluorescence intensity will be at a maximum and then decrease exponentially according to Equation 5 (Rendell, 1987 Lakowicz, 2006). 

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