Transient emission spectra

Taking advantage of these characteristics, Corma and coworkers (Atienzar et al., 2004) have described and validated an automatic system for high-throughput (HT) characterization of large libraries of solid materials by PL in the range of 350 800 nm. The system proposed is able to provide time-resolved transient emission spectra in the microsecond range and can be employed to characterize materials, particularly in the fields of catalysis and electroluminescence. 

In the present paper we describe an apparatus for recording transient emission spectra that yields data which approach the ideal multidimensional case. We emphasize in the discussion the advantages of multichannel detection for transient emission data. We also briefly compare our approach to alternative methods for recording time and wavelength resolved fluorescence data on the picosecond time scale. 

Dissociation constants determined by deconvolution of transient emission spectra Dissociation constants determined by UV-titrations with camphor Value represents an upper-limit estimate of the dissociation constant... 

If one ignores polarization effects, the ideal experimental data for the transient emission spectrum of a molecule would be a high resolution three dimensional plot of emission-intensity versus emission-wavelength and delay time after molecular excitation. Most published transient emission data, however, are of the form integrated emission intensity over all emission-wavelengths versus delay time. These data, obviously, have less useful information than the multidimensional approach. 

Our results also shed light on the long-lived PA3 band detected in transient PM measurements of P3BT (see Fig. 7-19) and can explain changes in the PA spectra observed in several ps transient measurements of films of PPV derivatives at energies around 1.8 eV [9, 25, 60J. In good PPV films the transient PA spectrum shows a PA band of excitons at 1.5 eV whose dynamics match those of the PL and stimulated emission (SE) [9J. However, in measurements of oxidized [25] or C60-doped films 60, there appears a new PA band at about 1.8 eV whose dynamics are not correlated with those of the PL and SE. Based on our A-PADMR results here, we attribute the new PA band at 1.8 eV to polaron pair excitations. These may be created via exciton dissociation at extrinsic defects such as carbo-... 

Figure 4. Absorption and emission spectra of Ru(bpy)s2+ and the excited state transient absorption spectrum of Ru(bpy)s2 Key A, absorption spectrum of Ru(bpy)s2V B, absorption spectrum of Ru(bpy)32+ and C, emission spectrum. Conditions room temperature, and aqueous solution. (Reproduced from Ref. 19c. Copyright 1981, American Chemical Society.)...

The total transient Stokes shift (v(O)-v(oo)) observed in our time resolved experiments of coumarin in bulk water was 820 cm"1. In the case of C343 adsorbed on Z1O2 it is 340 cm 1. From measurements of the time-zero spectrum, i.e. the emission spectrum of C343 before solvent relaxation, Maroncelli et al. estimated the Stokes shift from solvation to be 1953 cm 1 for C343 in water [8]. Thus the time resolution of our experiments allows to observe about 42% of the total solvation process. Especially the very initial part, containing the inertial response is missed. 

Photoluminescence is the radiation emitted by the recombination process and as such is a direct measure of the radiative transition. Information about non-radiative recombination can often be inferred from the luminescence intensity, which is reduced by the competing processes (Street 1981a). The most useful feature of the luminescence experiment is the ability to measure the emission spectrum to obtain information about the energy levels of the recombination centers. The transition rates are found by measuring the transient response of the luminescence intensity using a pulsed excitation source. Time resolution to about 10 s is relatively easy to obtain and is about the maximum radiative recombination rate. The actual recombination times of a-Si H extend over a wide range, from 10 s up to at least 10- s. 

Figure 5 shows the absorption spectrum of irradiated SAA and the emission spectrum of irradiated SAT. As can be seen, the spectra are red-shifted compared to the corresponding spectra of the cis-quinoid tautomers by about 2000 cm . The transient observed after flashing a liquid solution shows a spectrum similar, although structureless, to the photoproduct in solid solution (Fig. 6). 

Many features of the emission spectrum can show time dependence, including the spectral shape (l,3 (v-9), the peak intensity, the linear polarization (10) and, in principle, the circular polarization (11). In extreme cases, the emission spectrum can actually have two separate fluorescence bands from two different isomers of the electronically excited molecules (12-15). For molecules with this behavior, it is possible to determine the kinetics of excited state isomerization by transient emission spectroscopy. 

Transient infrared spectroscopy (TIRS) is a mid-infrared technique [82] that has been developed to obtain spectra of moving solids and viscous liquids. TIRS spectra are obtained from the generation of a thin, short-lived temperature differential that is introduced by means of either a hot or cold jet of gas. When a hot jet is used, an emission spectrum is obtained from the thin, heated surface layer. This technique is known as transient infrared emission spectroscopy (TIRES). When a cold jet is used, the blackbody-like thermal emission from the bulk of the sample is selectively absorbed as it passes through the thin, cooled surface layer. The result is a transmission spectrum convoluted with the observed thermal spectroscopy. This method is known as transient infrared transmission spectroscopy (TIRTS). TIRS is ideally suited for online analysis because it is a single-ended technique that requires no sample preparation. This technique has been applied to the lignin analysis of wood chips [83]. 

Thiazyl monomer is a radical with one unpaired electron. In contrast to nitric oxide, it polymerizes so readily that it cannot be isolated as a monomeric solid or liquid and has only a transient existence in the gas phase. Thiazyl monomer may be generated in a number of ways, including the volatilization of (SN) c (2) or pyrolysis of S4N4 (1) over quartz wool above 300 °C. The emission spectrum and ESR spectrum have been reported. The bond length is calculated to be 149.7 pm from its spectroscopic moment of inertia. This indicates a bond order of between two and three. The dissociation energy of this strong sulfur-nitrogen bond is estimated to be 463 kj mol from spectroscopic data. Nevertheless, like other sulfur nitrides, NS is endothermic and unstable with respect to its elements. Thiazyl monomer exhibits an IR band at 1209 cm T The experimental dipole moment is 1.83 0.03 D and the ionization potential is 9.85 eV. 

Fig. 48. DLTS measurement time constant t (inverse of rate window) versus the inverse temperature of the peak in the electron emission spectrum at that r for a typical sample. The activation energy of 0.94 eV is the slope of the raw data without the 2kT correction (see text). The circles are from DLTS spectra the triangles are calculated from directly recorded capacitance transients.

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