Complexes emission spectra

Opposite behavior was displayed by molten fluoride systems. For instance, no bands were observed in the thin layer emission spectrum of a KF - K2SiF6 melt, whereas increasing the melt layer to 10-20 mm led to the appearance of two intensive bands at 730 and 476 cm 1. These bands correspond to v3 and v4 vibrations of the complex ion SiF62 Solid K2SiF6 is characterized by IR absorption bands at 741 and 483 cm 1 [343]. 

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,... 

Fig. 1.5 Fluorescence emission spectrum of the luciferase-oxyluciferin complex in the same solution as in Fig. 1.4 (solid line), compared with the luminescence spectrum of firefly luciferin measured in glycylglycine buffer, pH 7.6 (dotted line). The former curve from Gates and DeLuca, 1975 the latter from Selinger and McElroy, 1960, both with permission from Elsevier.

Theory. If two or more fluorophores with different emission lifetimes contribute to the same broad, unresolved emission spectrum, their separate emission spectra often can be resolved by the technique of phase-resolved fluorometry. In this method the excitation light is modulated sinusoidally, usually in the radio-frequency range, and the emission is analyzed with a phase sensitive detector. The emission appears as a sinusoidally modulated signal, shifted in phase from the excitation modulation and partially demodulated by an amount dependent on the lifetime of the fluorophore excited state (5, Chapter 4). The detector phase can be adjusted to be exactly out-of-phase with the emission from any one fluorophore, so that the contribution to the total spectrum from that fluorophore is suppressed. For a sample with two fluorophores, suppressing the emission from one fluorophore leaves a spectrum caused only by the other, which then can be directly recorded. With more than two flurophores the problem is more complicated but a number of techniques for deconvoluting the complex emission curve have been developed making use of several modulation frequencies and measurement phase angles (79). 

The atomic spectra of most elements are complex and show little regularity. However, the emission spectrum of the hydrogen atom is sufficiently simple to be described by a single formula ... 

The complexity of the Co emission spectrum and the low fraction of the desired 14.4 keV radiation require an efficient Mossbauer counting system that is able to discriminate photons of different energies and reject the unwanted events. Otherwise a huge nonresonant background would add to the counting statistics of the spectra and fatally increase the noise of the spectrometer. 

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 ... 

Fig. 8.3. The basis of linear unmixing. Unnormalized emission spectra of the three capillaries are shown in panel A. The linear unmixing algorithm is based on the hypothesis that a complex emission spectrum (an emission spectrum of a sample containing 2 or more fluorophores) can be modeled as a weighted sum of the emission spectra of the individual fluorophores present. Thus, the Mix spectrum should be the sum of the Cerulean and Venus spectra after each is multiplied by an abundance factor. In panel B the abundance factor for Venus is held at a value of 1, while the value of the Cerulean abundance factor is varied from 0.6 to 1.4. Because the Cerulean and Venus capillaries each contained 10 /iM of fluorophore, an abundance range of 0.6-1.4 corresponds to a concentration range of 6-14 /iM. In panel C the Cerulean abundance factor is held at a value of 1 (10 /rM) while the abundance factor for Venus was altered from 0.2 to 1 (2-10 /rM). Note that when the Cerulean spectrum was multiplied by 1 (corresponding to 10 /rM) and added to the Venus spectrum multiplied by 0.6 (corresponding to 6 /rM), the linear unmixing model matched the complex spectrum measured for the mix capillary.

The emission spectrum of the PEG-2N2 complex consisted of a large contribution from a collective excitation due to the interaction of two neighboring naphthyls and a small contribution from isolated (monomeric) naphthyls (see Fig. 12). This differs from the emission spectrum for the a-CD-PEG-2N2,... 

With spectroscopic methods it is possible to obtain information about the conformation of hydrocarbon-DNA complexes. The fluorescence quantum yields of aromatic hydrocarbons are greatly reduced when they bind to DNA in intercalated conformations. Figure 3 shows how the intensity of the emission spectrum of DMA decreases with increasing concentrations of DNA in 15% methanol. (In Figure 3 and throughout this discussion DNA concentrations and association constants have been reported in terms of PO molarity unless otherwise indicated. The solution content of organic solvents is given in percent volume.)... 

Different lanthanide metals also produce different emission spectrums and different intensities of luminescence at their emission maximums. Therefore, the relative sensitivity of time-resolved fluorescence also is dependent on the particular lanthanide element complexed in the chelate. The most popular metals along with the order of brightness for lanthanide chelate fluorescence are europium(III) > terbium(III) > samarium(III) > dysprosium(III). For instance, Huhtinen et al. (2005) found that lanthanide chelate nanoparticles used in the detection of human prostate antigen produced relative signals for detection using europium, terbium, samarium, and dysprosium of approximately 1.0 0.67 0.16 0.01, respectively. The emission... 

An emission spectrum for pure mercury obtained from a mercury lamp. It is easy to see that mixed sources, and higher energy excitation will produce very complex patterns of lines, demanding high quality optical... 

Programming a CAM for fluorometry is far more complex than for spectrophotometry. Spectrophotometry is simple because it is based on the ratio of light in to light out. But fluorometry creates many of the problems associated with true radiometry—measuring the emission spectrum of an unknown source. The logic may become circular. Radiometry to determine an emission spectrum requires the relative spectral sensitivity of the photometer to be known, but how can this be determined without a source with a known emission spectrum Fortunately, physicists in our national standardization organizations provide us with calibrated sources and photometers. 

The broad PL emission spectra of some metal chelates match the requirements for white emission. Hamada et al. investigated a series of Zn complexes and found bis(2-(2-hydroxy-phenyl)benzothiazolate)zinc (Zb(BTZ)2, 246) is the best white emission candidate. An OLED with a structure of ITO/TPD/Zn(BTZ)2/OXD-7/Mg In showed greenish-white emission with CIE (0.246, 0.363) with a broad emission spectrum (FWHM 157 nm) consisting of two emission peaks centered at 486 and 524 nm (Figure 3.14) [277], A maximum luminance of 10,190 cd/m2 at 8 V was achieved. The electronic and molecular structure of Zn(BTZ)2 have been elucidated by Liu et al. [278]. There is evidence that the dimeric structure [Zn(BTZ)2]2 in the solid state is more stable than its monomer Zn(BTZ)2. They also found that the electron transport property of Zn(BTZ)2 is better than that of Alq3. 

When excited, the molecules of organic dyes tend to form complexes with unexcited molecules like themselves. These excited dimeric complexes are called the excimers. The excimer emission spectrum is easy to observe because it is very different from that of a monomer. It is usually broad and strongly shifted to longer wavelengths, and it does not contain vibrational structure. If the excimer is not formed, we observe emission of the monomer in the fluorescence spectra, and upon its formation there appears a characteristic emission of the excimer. 

Since the same dye molecules can serve as both donors and acceptors and the transfer efficiency depends on the spectral overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor, this efficiency also depends on the Stokes shift [53]. Involvement of these effects depends strongly on the properties of the dye. Fluoresceins and rhodamines exhibit high homo-FRET efficiency and self-quenching pyrene and perylene derivatives, high homo-FRET but little self-quenching and luminescent metal complexes may not exhibit homo-FRET at all because of their very strong Stokes shifts. 

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