Absorption, excitation, and emission

Fluorescent and phosphorescent substances are excited into an unstable energy state by UV light. When they return to the ground state they release a part of the energy taken up in the form of radiation. The emitted radiation is less energetic than the light absorbed and usually lies in the visible part of the spectrum. Since absorption (excitation) and emission obey a linear relationship over a certain range a reduction in absorption leads to a reduction in the luminescence, too. 

Figure 5.7 Room-temperature electronic absorption, excitation and emission spectra for 2 in aqueous solution. The excitation spectrum of 2 was recorded by monitoring emission at 400 nm. Reproduced with permission from [31]. Copyright (2004) Royal Society of Chemistry.

Representative absorption (excitation) and emission spectra of a fluoro-chrome are provided in Fig. 1. Some degree of overlap between the two spectra is typical, and often the excitation and emission spectra are mirror images of each other. The separation between the wavelengths at which excitation and emission maxima occur is referred to as the Stokes shift. 

Cu Y. The absorption, excitation, and emission spectra of the Cu Y specimen were reported earlier (4, 10). The emission line is a perfect Gaussian centered at 18400 cm-- - (543 nm) of... 

Absorption, Excitation, and Emission Bands of the Alkaline-Earth Oxide Powders... 

Table 2.4 Peak positions of the absorption, excitation and emission spectra of the alkaline earth oxides.

The excitation and absorption spectra of ODA as a function of concentration are shown in Figures 10a and 10b, respectively. At low concentration, of about 10"6 M, the excitation maxima correspond to the absorption maxima however, as the concentration is increased the excitation maxima red shift while the absorption maxima remains constant. At a concentration of 10"2 M there is a single excitation peak with total self absorption for all wavelengths below 350 nm. The red edge absorption, excitation and emission band positions of ODA are summarized in Table IV. 

Representative absorption (excitation) and emission spectra of a fluorochrome are provided in Fig. 1. Some degree of overlap... 

The phenomenon of "temperature-broadening" was also first solved by Williams and Hebb (1951). By using a Gaussian harmonic oscillator, these authors solved the problem of obtaining the shape of absorption (excitation) and emission bands for the quantum mechanical case, namely-... 

Pan Z, Ning L, Cheng B-M, Tanner PA (2006) Absorption, excitation and emission spectra of SrCl2 Eu L Chem Phys Lett 428 78-82... 

Figure 4.3 Characterization of NIR-emitting PEGylated AuNPs (PEG-AuNPs). (A) Scheme of the particle synthesis. (B) Typical TEM image of the synthesized PEG-AuNPs. (C) Core size measured by TEM, and hydrodynamic diameter (HD) in PBS measured by dynamic light scattering (DLS). (D) Absorption, excitation, and emission (l = 350 nm) spectra of the PEG-AuNPs in PBS at pH 7.4. (Reproduced from ref. 48 with permission from John Wiley and Sons. Copyright 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim.)...

Luminescent Properties The (La, Tb)P04 phosphor has very weak absorption lines at the ultraviolet region, but by adding Ce " this phosphor results in a remarkable increase in absorption and emission intensity because Ce " can act as an efficient sensitizer to Tb ". The absorption, excitation, and emission spectra are shown in Fig. 8.4a. As presented, the absorption and excitation spectrum shows a broad band in UV region with a dominant peak at approximately 280 nm. The emission spectmm remains the characteristic emission peak of Tb " with a dominant peak at 543 nm. Similar to (Ce, Tb)MgAlnOi9, energy transfer from Ce " to... 

Fig. 8.4 a Absorption, excitation and emission spectra of (La, Ce, Tb)P04. Reprinted with permission from reference [20]. Copyright 2000 American Chemical Society, b Effects of fluxes on luminance of (La, Ce, Tb)P04 [19]... 

For an optical probe that displays a wavelength shift in absorption or emission on binding, the analyte concentration may be determined from a ratio of intensities at two wavelengths. This is known as a wavelength-ratiometric approach and avoids some of the limitations mentioned above for intensity-based sensing, since, the measurements are independent of probe concentration. Absorption-, excitation-and emission-based ratiometric measurements are all possible. 

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