Sensitization emission spectra

A. Phase-Sensitive Emission Spectra of a Two-Component Mixture... 

Phase-Sensitive Spectra and Spectral Relaxation Phase-sensitive emission spectra were obtained for N-acetyi-L-tryptophanamide in propylene glycol at various temperatures (Figure 22.23). These spectra were recorded following adjustment of tha detector phase to suppress the emission on the blue or the red side of the emission. Explain tha phase-sensitive spectra in Figure 22.23 in terms of the rates of spectral relaxation. 

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 excited state redox potential of a sensitizer plays an important process. An approximate value of the excited state redox potential potentials of the ground state couples and the zero-zero excitation Equations (13) and (14). The zero-zero energy can be obtained from of the sensitizer 38 role in the electron transfer can be extracted from the energy (E0 0) according to the 77 K emission spectrum... 

An increase in sensitivity and reliability of chip analysis can also be achieved by using fluorescence resonance energy transfer (FRET). For this purpose both the probe and the target are labeled with a fluorophor. When the emission spectrum of the donor, e.g. Cy5, overlaps with the absorption spectrum of the acceptor, e.g. Cy5.5, and the donor and the acceptor are at a certain distance from each other, energy is transferred from the donor to the acceptor on excitation of the donor fluorophor. 

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... 

Because of the high sensitivity of Ti-containing luminescence centers to their local environments, photoluminescence spectroscopy can be applied to discriminate between various kinds of tetrahedral or near-tetrahedral titanium sites, such as perfectly closed Ti(OSi)4 and defective open Ti(OSi)3(OH) units. Lamberti et al. (49) reported an emission spectrum of TS-1 with a dominant band at 495 nm, with a shoulder at 430 nm when the sample was excited at 250 nm. When the excitation wavelength was 300 nm, the emission spectrum was characterized by a dominant band at 430 nm with a shoulder at 495 nm. These spectra and their dependence on the excitation wavelength clearly indicate the presence of two slightly different families of luminescent Ti species, which differ in their local environments, in agreement with EXAFS measurements carried out on the same samples. 

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. 

In the specific case of sodium the resulting emission spectrum shall exhibit characteristic yellow lines. The spectrum is so highly sensitive that even the traces of Na show yellow lines distinctly. 

In the case of other elements, for instance Uranium, the emission spectrum normally displays thousands of narrowly spaced lines. However, the emission source possesses a fixed amount of energy which shall be spread up eventually amongst the thousands of lines thereby minimizing the sensitivity of each line. Hence, it is rather difficult to examine the less sensitive complex spectra of elements such as uranium. 

There is a small solvent dependence for [Ru(L)3]2+complexes which depends on the structure of L. The emission spectra of the Ru(bpy)32+ is mildly sensitive to media, the Ru(phen)32+ much less so, and the Ru(Ph2phen)32+ is virtually media independent. This decreasing sensitivity to solvent perturbation is a consequence of the excitation being localized in the metal a-diimine portion of the complex (-N=C-C=N).(27) The more extended the complex, the greater the shielding of the excited portion and the smaller the solvent perturbations of the emission spectrum. In particular, the bulky phenyl groups are extremely effective at shielding the excited state from environmental perturbations. 

When tryptophan is dissolved in water, it shows the fluorescence characteristics illustrated in O Figure 5-2. However, one especially useful property of tryptophan fluorescence is that its emission spectrum is highly sensitive to the polarity of its environment. In less polar solvents (alcohols, alkanes, etc.), the emission... 

The lines at 686 and 693 nm with a long decay time of approximately 1 ms in the titanite emission spectrum are not correlated with any other lines and bands (Fig. 4.34). Such lines are very typical for Cr in a high field coordination and may be connected with such a center. The broad luminescence band appears peaking at 765, which may be ascribed to Cr + in a weak field coordination. The band at 765 nm has distinct dips at 749, 762, 793, 798, 804 and 820 nm. Comparison with the titanite absorption spectrum (Fig. 5.19) demonstrates that those lines exactly coincide with the absorption spectrum of Nd (Bakhtin and Gorobets 1992). Cr is a good energy sensitizer, because it has broad, allowed absorption bands with a broad emission spectrum, which overlaps the absorption bands of the lasing ion (Nd " ", Ho " ). 

Shown in Figure 5 is the emission spectrum for LaOBr.002Tb (23). At these terbium concentrations, the principal emissions occur at 380, 415 and 440 nm which can be used with blue sensitive films. This phosphor is being used in Agfa-Gevaert Co. 

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