Absorption band narrowing

However, if the polymer film at 250 K is cooled rapidly to 245 K, no band at 339 is observed. Instead, as seen from Figure 4c, the absorption band narrows, becomes symmetrical and shifts to higher energy. The new narrow absorption band at 316 nm is assigned to the well-known, all-D conformation, represented in the 7/3 helical arrangement of polysilanes like ( -Bu2Si)n. Next, additional slow cooling to 240 K led to the formation... 

Magnetic nanoparticles showing Faraday rotation effect, and/or Kerr effect can be of interest in the fabrication of switches and devices. Size dependant transmittance and Faraday rotation have been found in maghemite ferrofluids and ferrite films." Multilayered assemblies of yttrium garnet nanoparticles show magnetization-induced second harmonic generation (Kerr effect)." In metal/PMMA nanocomposites, the main absorption band narrows and additional peaks appear when decreasing the particle size." ... 

Figure 2.4 (a) An absorption experiment, (b) A broad and (c) a narrow absorption band with the... 

From about 1970, but before the availability of suitable lasers, Parmenter and others obtained SVLF spectra, particularly of benzene, using radiation from an intense high-pressure xenon arc source (see Section 3.4.4) and passing it through a monochromator to select a narrow band ca 20 cm wide) of radiation to excite the sample within a particular absorption band. 

The farther into the uv and the narrower the distribution of the resonant electron frequencies, the smaller the effect of dispersion in the visible region. The Pb(II) ion exhibits absorption in the near-uv, and addition of Pb(II) to a glass increases both n and dispersion. However, the use of Ba(II) and La(III) increases n without increasing dispersion. Fluorophosphates, having absorption bands located well into the uv, are examples of glasses with high AbbH numbers and low refractive indexes. 

Infrared absorption spectra can be employed for the identification of pure compounds or for the detection and identification of impurities. Most of the applications are concerned with organic compounds, primarily because water, the chief solvent for inorganic compounds, absorbs strongly beyond 1.5//m. Moreover, inorganic compounds often have broad absorption bands, whereas organic substances may give rise to numerous narrower bands. 

As with electronic spectra, the use of infrared spectra for quantitative determinations depends upon the measurement of the intensity of either the transmission or absorption of the infrared radiation at a specific wavelength, usually the maximum of a strong, sharp, narrow, well-resolved absorption band. Most organic compounds will possess several peaks in their spectra which satisfy these criteria and which can be used so long as there is no substantial overlap with the absorption peaks from other substances in the sample matrix. 

The photochemical activity of pure Ti02 has been invesli ted extensively for decades, and it has been revealed that the primary limitation is poor solar spectrum photon absorption because of its wide band gap. Recently, it has been reported that narrowing band p,p can be achieved by doping TO2 with other elements such as nitrogen[7], sulfiir, caibon, etc. For example, fliara et al.[8] reported nitrogen doping shifts the absorption band as well as narrows the band gap. 

The interactions of photons with molecules are described by molecular cross-sections. For IR spectroscopy the cross-section is some two orders of magnitude smaller with respect to UV or fluorescence spectroscopy but about 10 orders of magnitude bigger than for Raman scattering. The peaks in IR spectra represent the excitation of vibrational modes of the molecules in the sample and thus are associated with the various chemical bonds and functional groups present in the molecules. The frequencies of the characteristic absorption bands lie within a relatively narrow range, almost independent of the composition of the rest of the molecule. The relative constancy of these group frequencies allows determination of the characteristic... 

In order to determine the structural factors maximizing 2PA cross section values, we analyze (8) from Sect. 1.2.1. For all cyanine-like molecules, symmetrical and asymmetrical, several distinct 2PA bands can be measured. First, the less intensive 2PA band is always connected with two-photon excitation into the main absorption band. The character of this 2PA band involves at least two dipole moments, /

symmetry forbidden for centro-symmetrical molecules, such as squaraines with C, symmetry due to A/t = 0, and only slightly allowed for polymethine dyes with C2V symmetry (A/t is small and oriented nearly perpendicular to /t01). It is important to note that a change in the permanent dipole moment under two-photon excitation into the linear absorption peak, even for asymmetrical D-a-A molecules, typically does not lead to the appearance of a 2PA band. 2PA bands under the main absorption peak are typically observed only for strongly asymmetrical molecules, for example, Styryl 1 [83], whose S0 —> Si transitions are considerably different from the corresponding transitions in symmetrical dyes and represent much broader, less intense, and blue-shifted bands. Thus, for typical cyanine-like molecules, both symmetrical and asymmetrical, with strong and relatively narrow, S (I > S) transitions, we observe... 

Fluorophores containing 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene as a core skeleton are commonly designated as BODIPY fluorophores. Due to their useful photophysical properties including high fluorescence quantum yields, high molar absorption coefficient, narrow absorption and emission band width, and their high photostability [50], BODIPY dyes are proven to be extremely versatile and useful in many biological applications Fig. 11 [68]. 



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