Reference emission spectra

As mentioned previously, the complex emission spectrum F (l) of samples containing multiple fluorophores is assumed to be the linear sum of individual component spectra Ffl), F2(X), FfX), weighted by their abundance xu x2, x3. Let Fj(X) and F2(X) be the reference emission spectra of pure samples of fluorophore (e.g., Cerulean and Venus). The term reference emission spectra is used because these spectra describe the emission at excitation wavelength /. x of a defined concentration of fluorophore (e.g., 10 /rM) acquired using the same excitation light intensity as was used to acquire an emission spectra of an unknown sample mixture. Under these conditions, the shape and magnitude of the fluorophore mixture spectra will be ... 

If reference emission spectra of a set of pure fluorophores are available, and if an emission spectrum of an unknown mixture of any combination of these fluorophores is acquired under the same conditions, this equation can be used to determine the abundance of the different fluorophores in the mixture. The use of this equation to determine the abundance of the fluorophores present is called linear unmixing. To illustrate the basis of linear unmixing, we will first use this equation to analyze the emission spectra of the mix capillary containing an unknown mixture of Cerulean and Venus depicted in Fig. 8.1. The unmixing approach we describe will utilize reasonable guesses for the values of x1 (representing the abundance of Cerulean) and x2 (representing the abundance of... 

With the signal S detected and the reference emission spectra R known, the contributions A of the fluorophores in the sample are determined by calculating contribution values that most closely match the detected signals in the channels. This can be done by a least-square fitting approach that minimizes the square difference between calculated and measured values with the following set of differential equations ... 

It is the reference emission spectrum of the donor, multiplied by its abundance, but attenuated by the fraction of donors that are not transferring energy by FRET. The second part of the equation describes emission from directly excited acceptors ... 

It is simply the reference emission spectrum of the acceptor, multiplied by the abundance of acceptor. Finally, the last part of the equation represents the energy transferred from directly excited donors to acceptors by FRET, and then emitted as acceptor fluorescence ... 

Finally, a word on terminology. Many AI methods learn by inspecting examples, which come in a variety of forms. They might comprise a set of infrared spectra of different samples, the abstracts from a large number of scientific articles, a set of solid materials defined by their composition and their emission spectrum at high temperature, or the results from a series of medical tests. In this text, we refer to these examples, no matter what their nature, as "sample patterns."... 

Certain features of light emission processes have been alluded to in Sect. 4.4.1. Fluorescence is light emission between states of the same multiplicity, whereas phosphorescence refers to emission between states of different multiplicities. The Franck-Condon principle governs the emission processes, as it does the absorption process. Vibrational overlap determines the relative intensities of different subbands. In the upper electronic state, one expects a quick relaxation and, therefore, a thermal population distribution, in the liquid phase and in gases at not too low a pressure. Because of the combination of the Franck-Condon principle and fast vibrational relaxation, the emission spectrum is always red-shifted. Therefore, oscillator strengths obtained from absorption are not too useful in determining the emission intensity. The theoretical radiative lifetime in terms of the Einstein coefficient, r = A-1, or (EA,)-1 if several lower states are involved,... 

Figure 17. Modulation index as a function of applied C02 concentration. 0%, 15.6%, 33.0%, 52.5%, 74.7% and 100% C02 concentration was applied to the measurement cell. The 90 cm long reference cell, contained 100% C02, and the 30 cm long measurement gas cell, contained 100% C02, were at 1 Bar and 20 °C. The optical LED emission spectrum was centred at 2.04 pm and had a 150 nm FWHM bandwidth.

Figure 12.7 Electronic transitions giving rise to the emission spectrum of sodium in the visible, as listed in Table 12.1. The principal series consists of transitions from the 3s level to 3p or a higher p orbital the sharp series from 3p to 4s or a higher s orbital diffuse from 3p to 3d or above and the fundamental from 3d to 4/or higher. The terms below the lines [(R/(3-1.37)2, etc.] are the quantum defect corrections referred to in Section 10.4.

Figure 22. Schematic overlay of the most intense IR absorptions for neutral acetone and acetone-dg with a 300-K blackbody emission spectrum. The intensity axis refers to the blackbody radiation only.

Inner-filter effects. The absorption of the fluorescence excitation and emission by the specimen is referred to as the "inner-filter" effect this effect has been treated in the literature (24-27). The inner-filter effect reduces the signal levels and distorts the emission spectrum and the intensity-concentration relationship. The effect is more pronounced in right-angle fluorescence measurements (27) than in the "front face" configuration in which the fluorescence is viewed from the same side as the excitation beam. 

Figure 7. A, Atmospheric emission spectrum of region near that used by Traub et al. (85) to quantify stratospheric H02 concentrations. B, A laboratory H02 spectrum. C, The best-fit calculated spectrum. (Reproduced with permission from reference 85. Copyright 1990 American Association for the Advancement...

According to the Forster cycle, if the longest wavelength electronic transition of the deprotonated form is of lower energy compared to that of the protonated form (red-shifted electronic absorption or emission spectrum of the deprotonated form with reference to the protonated-form spectrum), the molecule has enhanced excited-state acidity (i.e., the pK a of the molecule is lower than pKa). Equation (1) provides a quick and effective method for evaluating a molecule for its ESPT behavior. 

The prism at the outlet of the laser serves to separate the laser emission of the gas fluorescence and allows for a clean excitation of the sample. For excitation using solid-state lasers, this element is dispensable. The lens (element 5) collects the fluorescent signal and focuses on the aperture of the monochromator. The filter is used to eliminate excitation that is spread over the surface of the sample. The optical chopper serves to modulate the light at a defined frequency, which serves as reference for the lock-in amplifier. A data acquisition system controls the pace of the monochromator and reads the signal of the lock-in, generating the sample s emission spectrum. 

Fig. 9.62 a Fluorescence spectra (345 nm excitation) of the oFL reference (pink spectrum), 24a (iorange spectrum) and 24b (brown spectrum) in toluene representing the quenching of the oFL emission, b Fluorescence spectra of the C60 reference (black spectrum), 24a (orange spectrum) and 24b (brown spectrum) in toluene representing the quenching of the C60 emission... 

Figure 2-14 Neon lamp emission spectrum. Band numbers refer to Table 2-8 in (a) and Table 2-9 in (b).

Fig. 26. Energy level diagram for the triplet sublevels of (a) perprotonated, (b) partially deu-terated, and (c) perdeuterated Pt(2-thpy)2 dissolved in an n-octane matrix (Shpol skii matrix). Emission decay times and spin-lattice relaxation times are given for T= 1.3 K. Several vibrational satellites are specified, HT = Herzberg-Teller active vibration, FC = Franck-Condon active vibration. The emission spectrum of the partially deuterated compound (b) exhibits vibrational satellites of the two different ligands. (Compare Fig. 27b.) The data given for Pt(2-thpy-hg)(2-thpy-d6) (b) refer to the lower lying site A. (Compare Ref. [23])...

FIGURE 3. Emission spectrum and eight-fold coordination polyhedron of [Eu(tta)2(N03)(tppo)2] . Reproduced with permission from Reference 38, Copyright 2008 Elsevier... 

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