Excited and fluorescence

When recording excitation and fluorescence spectra it must be ensured that monochromatic light falls on the detector This can best be verified in instruments built up on the kit principle or in those equipped with two monochromators (spectrofluonmeters) The majority of scanners commercially available at the moment do not allow of such an optical train, which was realized in the KM3 chromatogram spectrometer (Zeiss) So such units are not able to generate direct absorption or fluorescence spectra for the charactenzation of fluorescent components... 

Principles and Characteristics Atomic fluorescence spectrometry (AFS) is based on excitation of atoms by radiation of a suitable wavelength (absorption), and detection and measurement of the resultant de-excitation (fluorescence). The only process of analytical importance is resonance fluorescence, in which the excitation and fluorescence lines have the same wavelength. Nonresonance transitions are not particularly analytically useful, and involve absorption and fluorescence photons of different energies (wavelength). 

The corrected excitation and fluorescence spectra of PET-4,4 -SD copolymers in HFIP solution or as yarns were identical to the spectra of PET homopolymer. The uncorrected phosphore-sence excitation and emission spectra of PET-4,4 -SD copolymer yarns were also identical to that of the PET homopolymer yarn. 

The structure of the fluorescent molecule can also contribute substantially to the overall efficiency of a chemiluminescent process. Excitation and fluorescence can be strongly influenced by the structure of the fluorescer. 

Class C Fluorophores that undergo no photoinduced proton transfer but only photoinduced electron transfer. The fluorescence quantum yield of these fluorophores is very low when they are in the non-protonated form because of internal quenching by electron transfer. Protonation (which suppresses electron transfer) induces a very large enhancement of fluorescence (see Section 10.2.2.5). The bandshapes of the excitation and fluorescence spectra are independent of pH. 

As described above, two-photon excitation microscopy provides several advantages (reduced photobleaching, deeper penetration into the specimen). A fluorescence microscope combining two-photon excitation and fluorescence time-resolved... 

A variety of optical alignment accessories for the launch of the excitation light into the fiber optic temperature probe, the collection of the fluorescence response, and optical filters used to isolate the excitation and fluorescence emission at the detector and in some cases at the excitation source as well. 

Low transit-time dispersion with photon wavelength, i.e., < 0.5 psec/nm. This minimizes the effect on convolution of the difference between the excitation and fluorescence wavelengths. Both side-window and linear focused photomultipliers satisfy this. 

The excitation and fluorescence spectra of some crown ether complexes have been interpreted in terms of the molecular point group symmetry and vibronic coupling.452,453 This approach tends to be limited to europium(III) complexes. 

These reactions are, respectively, photostimulation [at a rate F(f) species per second], fluorescence from the excited fluorophor, non-radiative de-excitation, and fluorescence quenching. Consider, for instance, that the photostimulation only occurs at time t — f0 that is, F(t) = F05(f — f0). Then, the concentration of the excited fluorophor [A ] varies according to... 

The absorption and emission maxima from this table will provide clues to the spectral ranges that are useful for excitation and for fluorescence detection with a particular fluorochrome. However, the absorption and emission spectra have breadth, with slopes and shoulders and secondary peaks (see Fig. 5.6). With efficient fluorochromes, excitation and fluorescence detection at wavelengths distant from the maxima may be possible. Therefore, inspection of the full, detailed spectra is necessary to get the full story. In addition, spectra may shift in different chemical environments (this will explain why maxima vary in different reference tables from different sources). Values in this table are derived primarily from the Molecular Probes Handbook and the article by Alan Waggoner (Chapter 12) in Melamed et al. 

Measured and computed values of the matrix coefficient are shown in Table 7.13. The values agree within a few percent except for Fe and Mn in radishes, where the difference is 6%. A matrix correction factor of 2 means that the combined attenuation of the exciting and fluorescent X-rays is 50%. In radishes, about half of this figure is from the cellulose and the other half from the presence of 6% potassium. 

FWAs can only improve whiteness effectively if the substrate does not absorb too strongly in their excitation and fluorescence range. Objects with a poor basis white, such as unbleached textiles or poorly cleaned articles, cannot be brightened to a high degree of whiteness even with high concentrations of FWAs [119],... 

This proton transfer can be seen in both the excitation and fluorescence spectra. 

In the following we consider the nature of LIFS in more detail. The theoretical foundations of laser excitation and fluorescence are outlined and such issues as detectability and dynamic range are discussed. Finally the status of LIFS is summarized and a prognosis for future development given. 

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