Wavelength of maximum emission

The Wien displacement law states that the wavelength of maximum emission, A , of a blackbody varies inversely with absolute temperature the product A T remains constant. When A is expressed in micrometers, the law becomes... 

FIGURE 1.14 As the temperature is raised (1/7 decreases), the wavelength of maximum emission shifts to smaller values. 

Molecular fluorescence involves the emission of radiation as excited electrons return to the ground state. The wavelengths of the radiation emitted are different from those absorbed and are useful in the identification of a molecule. The intensity of the emitted radiation can be used in quantitative methods and the wavelength of maximum emission can be used qualitatively. A considerable number of compounds demonstrate fluorescence and it provides the basis of a very sensitive method of quantitation. Fluorescent compounds often contain multiple conjugated bond systems with the associated delocalized pi electrons, and the presence of electron-donating groups, such as amine and hydroxyl, increase the possibility of fluorescence. Most molecules that fluoresce have rigid, planar structures. 

All objects above absolute zero temperature (-273 °C) emit electromagnetic radiation in the IR region. Further, the emission of IR radiation is theoretically based on the concept of black body which is considered a perfect and efficient emitter. As the temperature of the object increases, wavelength of maximum emission shifts to the shorter wavelength region and therefore radiant energy is emitted in the IR and visible range. 

In 1977, Scharf and Mattay [123] found that benzene undergoes ortho as well as meta photocycloaddition with 2,2-dimethyl-1,3-dioxole and, subsequently, Leismann et al. [179,180] reported that they had observed exciplex fluorescence from solutions in acetonitrile of benzene with 2,2-dimethyl-l,3-dioxole, 2-methyl-l,3-dioxole, 1,3-dioxole, 1,4-dioxene, and (Z)-2,2,7,7-tetram-ethyl-3,6-dioxa-2,7-disilaoct-4-ene. The wavelength of maximum emission was around 390 nm. In cyclohexane, no exciplex emission could be detected. No obvious correlation could be found among the ionization potentials of the alkenes, the Stern-Volmer constants of quenching of benzene fluorescence, and the fluorescence emission energies of the exciplexes. Therefore, the observed exciplexes were characterized as weak exciplexes with dipole-dipole rather than charge-transfer stabilization. Such exciplexes have been designated as mixed excimers by Weller [181],... 

The standard solutions were diluted with hexane or methanol to prepare solutions that contained 2 yg/ml pesticide for the initial fluorescence measurements. Excitation and emission band widths on the spectrofluorometer were adjusted to 4 nm. A solution of quinine sulfate, 1 yg/ml in 0.1 N sulfuric acid, was used as a reference in determining the relative fluorescence intensity of the pesticides. The wavelengths for excitation and emission that would give the maximum fluorescence intensity in both hexane and methanol were obtained next by using 1 cm quartz fluorometer cells. Finally the excitation monochromator was set at 254 nm, and the fluorescence intensity was again measured at wavelength of maximum emission in both hexane and methanol. 

Table III shows that the luminescent lifetimes and the relative luminescent intensities for the covalently bound duplex and its noncovalent analogue are similar. As with [Ru(phen)2(dppz)]2+, a biexponential decay in emission is observed for the ruthenated oligonucleotide hybridized to its complement. A small shift in the wavelength of maximum emission is also observed compared to the noncovalent complex. This shift likely reflects the sensitivity in emission to the stacking of the oriented dppz ligand a dependence of the maximum emission wavelength on base...

Microstructural probes distances between molecules or functional groups, molecular orientation, molecular assemblies ( 1 f wavelength of maximum emission, I t fluorescence intensity, T t fluorescence lifetime,... 

Material Wavelength of maximum emission (nm) Scintillation efficiency (relative, %) Decay time (us) Density (10> kg/m>)... 

The Wien displacement law for blackbody radiators states that the product of temperature in kelvin and the wavelength of maximum emission is a constant k k - T - Calculate the wavelength of maximum emission for a Globar infrared source operated at 18(X) K. Use the data In Figure 6-22 for the Nernst glower for the evaluation of the constant. 

Material Density (g cm Wavelength of maximum emission (nm) Decay constant for emission (ps) Relative pulse height... 

Medium-Priced Uncorrected Spectrofluorometers. There are now available a number of so-called medium-priced spectrofluorometers. Some are equipped with a mercury source for optimum trace analysis, but a xenon source is also available. The important advantage of these instruments is that the variable-slit-width emission grating allows one to measure fluorescence at the wavelength of maximum emission using as narrow or wide a bandwidth as allowed by the instrumental design. 

The wavelength of maximum emission of the LED maximum light intensity was reached in /v100 usee. 

Maize seedlings were grown in a phytotron programmmed for a 16hr photoperiod (300 pE.m-. s i) and a 25 C/15 C day/night temperature. Fluorescence induction curves were obtained from DCMU infiltrated leaves using a laboratory-made fluorometer. The wavelength of maximum emission was 592 nm. The fluorescence was measured at 685 nm. 

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