Capabilities excitation spectra

If the observation monochromator is kept at the wavelength of the fluorescence maximum and the wavelength of the excitation monochromator is varied, a so-called excitation spectrum is obtained that resembles the absorption spectrum in its spectral distribution. If a mixture of substances contains only one component capable of fluorescence, a fluorescence excitation spectrum can be used to obtain spectral information about this specific component [28], [33],... 

Principles and Characteristics The analytical capabilities of the conventional fluorescence (CF) technique (c/r. Chp. 1.4.2) are enhanced by the use of lasers as excitation sources. These allow precise activation of fluorophores with finely tuned laser-induced emission. The laser provides a very selective means of populating excited states and the study of the spectra of radiation emitted as these states decay is generally known as laser-induced fluorescence (LIF, either atomic or molecular fluorescence) [105] or laser-excited atomic fluorescence spectrometry (LEAFS). In LIF an absorption spectrum is obtained by measuring the excitation spectrum for creating fluorescing excited state... 

F655 disappears from C on (A reduced) its major band at 468 nm in the excitation spectrum indicates that Chi b remains capable of transferring its excitation energy to the emitters of F675 and F705. 

The simplest fluorescence measurement is that of intensity of emission, and most on-line detectors are restricted to this capability. Fluorescence, however, has been used to measure a number of molecular properties. Shifts in the fluorescence spectrum may indicate changes in the hydrophobicity of the fluorophore environment. The lifetime of a fluorescent state is often related to the mobility of the fluorophore. If a polarized light source is used, the emitted light may retain some degree of polarization. If the molecular rotation is far faster than the lifetime of the excited state, all polarization will be lost. If rotation is slow, however, some polarization may be retained. The polarization can be related to the rate of macromolecular tumbling, which, in turn, is related to the molecular size. Time-resolved and polarized fluorescence detectors require special excitation systems and highly sensitive detection systems and have not been commonly adapted for on-line use. 

Si(Li) spectroscopy, with the capability of simultaneous quantitative analysis of 72 elements ranging from sodium through to uranium in solid, liquid, thin film and aerosol filter samples. The penetrating power of protons allows sampling of depths of several tens of microns, and the beam itself may be focussed, rastered or varied in energy. The use of a proton beam as an excitation source offers several advantages over other X-ray techniques, for example there is a higher rate of data accumulation across the entire spectrum which allows for faster analysis. 

Much worse than the oscillator strength is the line shape. The calculated absorption spectra has no similarity with what is experimentally seen. The calculated half-width is always smaller, typically by a factor of 2 the exact reasons for this are only speculated. It is common knowledge that a photodetachment process is capable of giving a very broad absorption spectrum, but a satisfactory method has not been developed to adopt this with the bound-bound transition of the semicontinuum models. Higher excited states (3p, 4p, etc.) have been proposed for the solvated electron, but they have never been identified in the absorption spectrum. 

Trivalent samarium activated minerals usually display an intense luminescence spectrum with a distinct hne structure in the red-orange part of the spectrum. The radiating term 65/2 is separated from the nearest lower level 11/2 by an energy interval of 7,500 cm This distance is too large compared to the energy of phonons capable to accomplish an effective non-radiative relaxation of excited levels and these processes do not significantly affect the nature of their spectra in minerals. Thus all detected lines of the Sm " luminescence take place from one excited level and usually are characterized by a long decay time. 

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