Lifetime data

Table 7.8 Summary of results obtained for the four Os Mossbauer transitions studied. The absorber thickness d refers to the amount of the resonant isotope per unit area. The estimates of the effective absorber thickness t are based on Debye-Waller factors / for an assumed Debye temperature of 0 = 400 K. For comparison with the full experimental line widths at half maximum, Texp, we give the minimum observable width = 2 S/t as calculated from lifetime data.

The second chapter by Peter Verveer and Quentin Hanley describes frequency domain FLIM and global analysis. While the frequency domain technique for fluorescence lifetime measurement is sometimes counterintuitive, the majority of the 10 most cited papers using FLIM have taken advantage of the frequency domain method as stated by these authors. The global analysis of lifetime data in the frequency domain, resolving both E and /d has contributed significantly to this advantage. 

Recently, a method used for the analysis of frequency-domain data has been proposed for the analysis of time-domain images. The AB-plot or phasor plot provides a useful graphical representation of lifetime data that can be used for the segmentation of the images prior to data fitting [47, 48], With this method, data fitting may be avoided in many instances. 

There remain challenges to overcome in the use of FLIM and FRET in the general laboratory environment. A clear understanding of the nature of fluorescence decay is necessary for the correct interpretation of FLIM data and care must be taken to use negative controls appropriately. The contamination of lifetime data by... 

Figure 6. Fluorescence decay profiles of trans-7,8-dihydroxy-7,8-dihydro-BP and 8,9,10,11-tetrahydro-BA measured at 23 °C with and without native DNA. Taken from refs. 14 and 15. The upper left-hand corner contains an instrument response profile. Emission and excitation wavelengths, lifetimes, and values of x2 obtained from deconvolution of the lifetime data are also given.

Fig. 69 The lifetime data of Wu et al. are represented by their regression lines and indicated in this figure by dashed and dotted lines. The continuous lines are calculated with Eq. 140 using the parameter values listed in Table 6...

According to the simple Eq. 115 and the full Eq. 140, the lifetime of a fibre measured at a constant load decreases with increasing orientation parameter. The dependence of the slope of the curve, log( b) vs ob, on the initial orientation distribution has been calculated for PpPTA fibres using Eq. 140. Figure 70 shows that at constant load for increasing orientation angle the lifetime curves become steeper, while at the same time the lifetime decreases. This effect has been observed for nylon 66 yarns as shown in Fig. 71, where the lifetime data... 

Chen and coworkers have developed two new phosphorescent blue emitters, which have two identical 2-(2,4-difluorophenyl)pyridine ligands and are derivatives of the Firpic compound, iridium(III) bis(4,6-difluorophenylpyridinato)-3-(trifluoromethyl)-5-(pyridin-2-yl)-1, 2,4-triazolate (Firtaz) and iridium(III) bis(4,6-difluorophenylpyridinato)-5-(pyridin-2-yl)-l//-tetrazolate (FirN4) (Scheme 3.90) [314]. Both these two blue emitters show a 10-nm blue-shift of the emission compared with Firpic. Unfortunately, the efficiency of such blue emitters is inferior to those of Firpic and Fir6. There is no lifetime data reported for such devices. 

Today, many red and green OLEDs have lifetimes exceeding 10,000 h (see one example in Table 10.3). Instead of testing the OLED at room temperature, an accelerated experiment may be useful. The operational lifetime of PLED was studied at several temperatures (25-85°C) by Parker et al. [110]. They found the changes in luminance were significantly accelerated at higher temperatures. From the lifetime data at several temperatures, the OLED lifetime at room temperature can be readily estimated. 

Explain the usefulness of quenching and sensitisation studies to an understanding of mechanistic problems and in providing energy and lifetime data. 

While an unquenched single Gaussian distribution cannot be differentiated from a discrete double decay, does quenching lifetime data reveal the existence of the... 

Our results demonstrated clearly that the lifetime data are more sensitive to subtleties of the micromechanistic photophysics. In this case we were able to establish inadequacies of the two-component model that were not detected by intensity quenching measurements alone. It is also clear that resolution of the detailed mechanism in these complex polymer systems will require even better lifetime data than we are able to obtain with a conventional flash lamp-based time-correlated photon counting system. 

The potential for using multiplexed single-photon counting to acquire fluorescence lifetime data from a distributed array of optical fiber sensors, each sensing a different analyte, has recently been demonstrated by Birch etal.(39,47) Figure 12.9 illustrates such a network to be used in conjunction with the arrangement shown in Figure 12.6. 

Pairwise EET rates cannot be directly measured in antenna systems. The closest approach to direct determination is offered on the one hand by time resolved picosecond and sub-picosecond absorption and fluorescence measurements and on the other hand by hole burning spectroscopies. Time resolved techniques do not detect transfer between isoenergetic sites. A somewhat more indirect approach to determining pairwise rates is that of analysing excited state lifetime data in terms of a particular antenna and an EET model. 

Using the lifetime data obtained from several different temperatures, an Arrhenius plot of I nr vs. 1/T was made. From the least sguares fit, the energy of activation was calculated to be 580cm... 

In Table 2, we show the room temperature x s for some selected alkanes, and among them there are lifetime data that were determined in quenching experiments. (Data for larger groups of alkanes are discussed in Refs. 48, 49, 51, 59-61, 72, and 73.) For the... 

This section contains a very brief resume of some of the more theoretical aspects of rare-earth relaxation phenomena. Just sufficient information is included to permit analysis of the lifetime data. To delve more deeply into this fascinating and complex subject leads one rapidly into the realm of theoretical physics, which is not the point of this review. Fuller accounts and details may be obtained from the references. 

Metlay believes that the fourth molecule might be considered a molecule of crystallization. As is clear from his lifetime data, there is a significant difference between the two species. He suggests that authors who followed the earlier preparation of Crosby et al. 142) may have studied the wrong compound. 

The pertinent fluorescent lifetime data may be summarized as follows ... 

Some positrons undergo annihilation prior to thermalization, provided the slowing down process is not too rapid this is illustrated by features present in the lifetime data for the noble gases shown in Figures 6.2, 6.5... 

Earlier, Crosby s group had developed a multiple state model for [Ru(bpy)3]2+142> M3,254) wj1jcj1 njceiy accounted for the observed temperature quantum yield and lifetime dependence below 77 K, and applied the same model to [Ru(trpy)2]2+ 25S. Three states (separated by 55 cm-1) accounted for the low-temperature lifetime data, in a picture very similar to that for [Ru(bpy)3]2+143. When we calculate the room-temperature lifetime for [Ru(bpy)3]2+ from this model, the proper order of magnitude is obtained, but not so for [Ru(trpy)2]2+. Admittedly this is a long extrapolation, but it suggests that other factors, less important in [Ru(bpy)3]2+, must play a dominant role in dictating the non-radiative decay in [Ru(trpy)2]2+. 

The lifetimes obtained from a preliminary analysis are summarized in Table 1 which also includes the B(E2) values extracted from the lifetime data. Fig. 2 shows a plot of B(E2) s (in Weisskopf Units) vs. spin of the depopulating state. 

For comparison purposes, the spectrum of LaV04 (excited at 330 nm) is given in Fig. 15. The spectra for steam aged LaY crystals containing low (1.29%) V levels is shown in Fig. 16. Luminescent lifetime data are given in Tables I and II. In all cases there are two components, (Tt and a T2), present. The T2 species are very short often exceeding limits of detection. 

TABLE II. LUMINESCENCE LIFETIME DATA FOR Sn PASSIVATED SAMPLES... 

Establishing q for Ndm is more problematic. For instance, an A factor of342 ns (rate constants are expressed in ns-1) can be calculated from lifetime data of the perchlorate salt (table 2), assuming q = 9. A similar value is reported for nitrate, 360 ns (Beeby and Faulkner, 1997),... 

Multiphonon deactivation is also caused by interaction with alcohol or other vibrations of the solvents, as illustrated in table 3, where Ndm lifetime data are reported for various salts in methanol, dmso and their deuterated analogs. One can estimate the rate constant knr of the deactivation process assuming that the radiative rate is not affected by deuteration knr =... 

Table 6 Spectral and Lifetime Data for Fluorescence from Excited Benzyl and Substituted Benzyl Radicals in Low-Temperature (77 K) Matrices...

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