Emission spectra also

NH,/ l>ci- in Rh(NH3)sCP+ is 1/19 in H2O and 17 in DMF [101]. This striking solvent effect was ascribed to the effect of solvent on kc. The width of the emission spectra also varies with solvent and it is possible that the E A2 separation is not invariant to solvent. Population changes could be responsible for some of the solvent effect, but there must be some specific dependence of the dissociation rate on solvent. 

Microcavity OLEDs fabricated on distributed Bragg reflectors (quarter wave stacks) [94]. Such OLEDs are fabricated on dielectric layers with significant dielectric contrast, so they narrow the emission spectrum by constructive interference. The narrow emission spectra also result in more efficient and more stable devices than regular OLEDs. The emission spectrum can be tailored to the specific sensor requirements (i.e., the absorption peak of the sensing element). 

In accordance with the conclusion derived from the absorption spectra, the emission spectra also reveal the partially ordered structure of the film. As in the case of absorption, I and Ij., the fluorescence intensities parallel and perpendicular to the dipping direction, respectively, differ appreciably, in this case by a factor of three to four. Much higher dichroic ratios have been found with other oriented systems, e.g. with highly aligned films consisting of blends of polyethylene with 1 wt.% MEH-PPV (see Chart 1.8) [31, 32]. The films, fabricated by tensile drawing over a hot pin at 110-120 °C, proved to be highly anisotropic (dichroic ratio >60), with the preferred direction parallel to the draw axis. 

Cls can effectively alter the emission spectra also by perturbing the initial emitting states of the transition. In the following, we discuss some typical features of the phenomenon in NO2, pyrazine, H2S and traris-butadiene. 

A comparison of the emission spectra also shows that the Eu ion in NaLu02 does show some emission at the position of the Do- F2 lines. This emission consists of weak, fairly broad lines. The relevant transitions occur because the ions of the host lattice vibrate. These vibrations can cause a deviation from pure inversion symmetry, which means that the electric-dipole transitions are no longer forbidden. 

The neutral porphin has one main and three weak fluorescence bands whereas the acid form has three prominent fluorescence bands (Fig. 10). Studies of Dher6 (23,24) have revealed a whole series of still weaker fluorescence bands extending into the infrared. The solid porphins have absorption spectra shifted toward longer wave lengths, and they show emission spectra also displaced to the red (e.g., solid etioporphin. Fig. 10). 

El-Sayed 28> has reported on the phosphorescence spectrum of [2.2]paracyclophane. The emission differs both in wavelength ( 4700 A) and in duration (3.3 s) from that of benzene ( 3400 A, 6 s) hence a favorable intersystem crossing from the lowest singlet to the emitting triplet state was inferred. The emission spectrum also indicates that interactions take place between the two aromatic nuclei in the triplet state. 

Flame emission spectroscopy Method that uses a flame to cause an atomized analyte to emit its characteristic emission spectrum also known as flame photometry. 

Description of Method. Quinine is an alkaloid used in treating malaria (it also is found in tonic water). It is a strongly fluorescent compound in dilute solutions of H2SO4 (f = 0.55). The excitation spectrum of quinine shows two absorption bands at 250 nm and 350 nm, and the emission spectrum shows a single emission band at 450 nm. Quinine is rapidly excreted from the body in urine and is easily determined by fluorescence following its extraction from the urine sample. 

Whereas the emission spectrum of the hydrogen atom shows only one series, the Balmer series (see Figure 1.1), in the visible region the alkali metals show at least three. The spectra can be excited in a discharge lamp containing a sample of the appropriate metal. One series was called the principal series because it could also be observed in absorption through a column of the vapour. The other two were called sharp and diffuse because of their general appearance. A part of a fourth series, called the fundamental series, can sometimes be observed. 

Some X-ray photoelectron spectrometers are equipped with monochromators that can be used to remove unwanted radiation, such as the continuous radiation and even some of the weaker characteristic X-rays such as K<,3, K 4, Kas, and Ko,6, from the emission spectrum of the anode. A monochromator can also be used to resolve the K i,2 line into its two components K i and Ka2- Using a monochromator has at least two beneficial effects. It enables the narrow, intense K<, line to be used to excite spectra at very high resolution. A monochromator also prevents unnecessary radiation (continuous, K<,2, Ka3, K<,4, Kas, and Ka6) that might contribute to thermal or photochemical degradation from impinging on the sample. 

Since an atom of a given element gives rise to a definite, characteristic line spectrum, it follows that there are different excitation states associated with different elements. The consequent emission spectra involve not only transitions from excited states to the ground state, e.g. E3 to E0, E2 to E0 (indicated by the full lines in Fig. 21.2), but also transisions such as E3 to E2, E3 to 1( etc. (indicated by the broken lines). Thus it follows that the emission spectrum of a given element may be quite complex. In theory it is also possible for absorption of radiation by already excited states to occur, e.g. E, to 2, E2 to E3, etc., but in practice the ratio of excited to ground state atoms is extremely small,... 

Latia luciferase is colorless and normally nonfluorescent. However, the luciferase fluoresces visibly in alkaline solutions. The fluorescence is most prominent in a KCN solution, showing an emission spectrum that is very close to the bioluminescence spectrum and also to the fluorescence emission of a flavin (FAD) except for the 370 nm... 

The emission spectrum observed by high resolution spectroscopy for the A - X vibrational bands [4] has been very well reproduced theoretically for several low-lying vibrational quantum numbers and the spectrum for the A - A n vibrational bands has been theoretically derived for low vibrational quantum numbers to be subjected to further experimental analysis [8]. Related Franck-Condon factors for the latter and former transition bands [8] have also been derived and compared favourably with semi-empirical calculations [25] performed for the former transition bands. Pure rotational, vibrationm and rovibrational transitions appear to be the largest for the X ground state followed by those... 

The synthetic alkaloid coralyne (Scheme 1) on the other hand is a planar molecule and is not readily soluble in aqueous buffers. It is highly soluble in ethanol and methanol. Coralyne is characterized by strong absorption maxima at 219, 300, 311, 326 and 424 nm with characteristic humps at 231, 360 and 405 nm in 30% (v/v) ethanol. It is highly fluorescent and gives an emission spectrum with a maximum at 460 nm when excitation was done either at 310 or 424 nm. It was observed that both absorbance and the fluorescence pattern of coralyne remained unaltered in buffer of various pH values ranging from 1.0 to 13.0 and also with salt concentration ranging from 4.0 to 500 mM. This implied that hydrophobic environment favoured the increment of their fluorescence properties [144]. 

The luminescence of macrocrystalline cadmium and zinc sulfides has been studied very thoroughly The colloidal solutions of these compounds also fluoresce, the intensity and wavelengths of emission depending on how the colloids were prepared. We will divide the description of the fluorescence phenomena into two parts. In this section we will discuss the fluorescence of larger colloidal particles, i.e. of CdS particles which are yellow as the macrocrystalline material, and of ZnS particles whose absorption spectrum also resembles that of the macrocrystals. These colloids are obtained by precipitating CdS or ZnS in the presence of the silicon dioxide stabilizer mentioned in Sect. 3.2, or in the presence of 10 M sodium polyphosphate , or surfactants such as sodium dodecyl sulfate and cetyldimethylbenzyl-ammonium... 

Fluorescent probes are divided in two categories, i.e., intrinsic and extrinsic probes. Tryptophan is the most widely used intrinsic probe. The absorption spectrum, centered at 280 nm, displays two overlapping absorbance transitions. In contrast, the fluorescence emission spectrum is broad and is characterized by a large Stokes shift, which varies with the polarity of the environment. The fluorescence emission peak is at about 350 nm in water but the peak shifts to about 315 nm in nonpolar media, such as within the hydrophobic core of folded proteins. Vitamin A, located in milk fat globules, may be used as an intrinsic probe to follow, for example, the changes of triglyceride physical state as a function of temperature [20]. Extrinsic probes are used to characterize molecular events when intrinsic fluorophores are absent or are so numerous that the interpretation of the data becomes ambiguous. Extrinsic probes may also be used to obtain additional or complementary information from a specific macromolecular domain or from an oil water interface. 

Absorption and Emission Spectra. The excitation-emission spectrum of 1 (bottom half of Fig. 1) shows that the relatively narrow emission band is nearly independent of the excitation wavelength and that the excitation spectrum is not only nearly independent of the wavelength at which the emission is monitored, but is also very similar to the absorption spectrum, both being somewhat broader than the emission band. This leaves no doubt that the observed emission is due to the polysilane, and its shape, location and the mirror image relation to the absorption permit its assignment as fluorescence. 

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