Steady-state emission spectroscopy

Several spectroscopic techniques have been used to study different aspects of conventional W/O/S microemulsion structures and properties. The absorption and steady-state emission spectroscopy of probe molecules solubilized in a microemulsion system can find the polarity of the microemulsion at their solvation location [34]. Time-resolved emission spectroscopy also provides information on the dynamics and rotation relaxation of solvent in both classical W/O/S and IL microemulsions [34-36]. Water content, which is defined as the molar ratio of water to total surfactant ([water]/[surfactant]), is one of the key factors in a microemulsion [37]. The ionization degree of bioactivator in IL microemulsion was correlated with the water content (cOj,) using UV-Vis absorption spectra, as shown in Rgure 18.2. 

It was established by steady-state luminescence spectroscopy that minerals of Mn, such as rhodonite, rhodochrosite, helvine, triplite, Mn-apatite, Mn-milarite and others, show dark red luminescence, mainly at 77 K, which is uncommon to impurity Mn ". The excitation center proved to be regular Mn ", while the emission center is Mn ", situated near some lattice defect (Gorobets et al. 1978 Gaft et al. 1981). 

The possible luminescence of Eu " in scheelite is a very interesting problem. It was not detected by steady-state luminescence spectroscopy. The possible reason is that the very strong intrinsic luminescence of scheehte is situated in the same spectral range, which covers the weaker emission of Eu ". We tried to solve this problem by the time-resolved method using different decay times for intrinsic and Eu bands. Time-resolved spectroscopy... 

Steady-state fluorescence spectroscopy has also been used to study solvation processes in supercritical fluids. For example, Okada et al. (29) and Kajimoto and co-workers (30) studied intramolecular excited-state complexation (exciplex) and charge-transfer formation, respectively, in supercritical CHF3. In the latter studies, the observed spectral shift was more than expected based on the McRae theory (56,57), this was attributed to cluster formation. In other studies, Brennecke and Eckert (5,31,44,45) examined the fluorescence of pyrene in supercritical CO2, C2HSteady-state emission spectra were used to show density augmentation near the critical point. Additional studies investigated the formation of the pyrene excimer (i.e., the reaction of excited- and ground-state pyrene monomers to form the excited-state dimer). These authors concluded that the observance of the pyrene excimer in the supercritical fluid medium was a consequence of increased solute-solute interactions. 

In this paper, we present a preliminary analysis of the steady-state and time-resolved fluorescence of pyrene in supercritical C02. In addition, we employ steady-state absorbance spectroscopy to determine pyrene solubility and determine the ground-state interactions. Similarly, the steady-state excitation and emission spectra gives us qualitative insights into the excimer formation process. Finally, time-resolved fluorescence experiments yield the entire ensemble of rate coefficients associated with the observed pyrene emission (Figure 1). From these rates we can then determine if the excimer formation process is diffusion controlled in supercritical C02. 

Shortite was studied by steady-state luminescence spectroscopy and luminescence of trivalent REE, such as Gd, Dy, Sm and Tb was found (Gorobets and Rogojine 2001). Excitation by CW laser with 532 and 780 nm revealed narrow luminescence lines possibly belonging to Nd " and two luminescence bands peaking at 650 and 705 nm (Fig. 4.54). Additional study is needed to ascribe those emission centers including their decay times and excitation spectra. 

It is a rare lead silicate which was not studied by steady-state luminescence spectroscopy. Laser-induced time-resolved technique (Figs. 4.64 and 4.65) enables to detect two types of Pb ", two types of Mn " and Ce emission centers (Gaft et al. 2013a). 

The luminescence of many titanium minerals was studied by steady-state luminescence spectroscopy and it was proposed that blue luminescence bands mutual for these minerals is connected with TiOe complex luminescence (Gaft et al. 1981a White 1990). Figure 4.82a presents spectral properties of the blue emission from benitoite at 300 K. Under short and middle-wave UV laser excitation, such as at 266 and 308 nm, respectively, an intensive broad blue emission band peaking at approximately 420 nm with half-width of 80 nm is detected. Spectra with different excitations, delays and gates revealed that this band consists of only one... 

Steady-State Emission and Transient Absorption Spectroscopy... 

Steady-state fluorescence spectroscopy refers to the measurement of the fluorescence intensity of a sample under the condition of constant illumination (excitation) of the sample. This results in a constant rate of absorption, and hence a constant rate of formation of the first excited singlet state. Si, as given by Eq. 3. This leads to the establishment of steady-state conditions, in which the rate of relaxation (decay) of the Si population is exactly the same as the rate of its formation. Thus, a constant Si population is established. Under these conditions, the rate of Eq. 4 ( = f[Si]), i.e. the rate of fluorescence emission, is constant. Since intensity (/p) is defined as the rate of photon emission per unit time (usually expressed in counts per second, cps), the measured fluorescence intensity is therefore constant with time. 

Steady-State Fluorescence Depolarization Spectroscopy. For steady state depolarization measurements, the sample is excited with linearly polarized lig t of constant intensity. Observed values of P depend on the angle between the absorption and emission dipole moment vectors. In equation 2 (9), Po is the limiting value of polarization for a dilute solution of fluorophores randomly oriented in a rigid medium that permits no rotation and no energy transfer to other fluorophores ... 

Seminal studies on the dynamics of proton transfer in the triplet manifold have been performed on HBO [109]. It was found that in the triplet states of HBO, the proton transfer between the enol and keto tautomers is reversible because the two (enol and keto) triplet states are accidentally isoenergetic. In addition, the rate constant is as slow as milliseconds at 100 K. The results of much slower proton transfer dynamics in the triplet manifold are consistent with the earlier summarization of ESIPT molecules. Based on the steady-state absorption and emission spectroscopy, the changes of pKa between the ground and excited states, and hence the thermodynamics of ESIPT, can be deduced by a Forster cycle [65]. Accordingly, compared to the pKa in the ground state, the decrease of pKa in the... 

Molecular rotors are useful as reporters of their microenvironment, because their fluorescence emission allows to probe TICT formation and solvent interaction. Measurements are possible through steady-state spectroscopy and time-resolved spectroscopy. Three primary effects were identified in Sect. 2, namely, the solvent-dependent reorientation rate, the solvent-dependent quantum yield (which directly links to the reorientation rate), and the solvatochromic shift. Most commonly, molecular rotors exhibit a change in quantum yield as a consequence of nonradia-tive relaxation. Therefore, the fluorophore s quantum yield needs to be determined as accurately as possible. In steady-state spectroscopy, emission intensity can be calibrated with quantum yield standards. Alternatively, relative changes in emission intensity can be used, because the ratio of two intensities is identical to the ratio of the corresponding quantum yields if the fluid optical properties remain constant. For molecular rotors with nonradiative relaxation, the calibrated measurement of the quantum yield allows to approximately compute the rotational relaxation rate kor from the measured quantum yield [Pg.284]

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