Fluorescence lifetime, temperature dependence

If rate constants are competitive, we expect the emission of prompt fluorescence, phosphorescence and delayed fluorescence of energy quanta /7v/, h jp and //vn) respectively. Although //v/ is equal to ftvED, the lifetime of delayed fluorescence will match the lifetime of triplet decay. The rate constant ArEn for E-type delayed fluorescence is temperature dependent and can be expressed as... 

The validity of the above conclusions rests on the reliability of theoretical predictions on excited state barriers as low as 1-2 kcal mol . Of course, this required as accurate an experimental check as possible with reference to both the solvent viscosity effects, completely disregarded by theory, and the dielectric solvent effects. As for the photoisomerization dynamics, the needed information was derived from measurements of fluorescence lifetimes (x) and quantum yields (dielectric constant, where extensive formation of ion pairs may occur [60], the observed photophysical properties are confidently referable to the unperturbed BMPC cation. Figure 6 shows the temperature dependence of the... 

As in the case of intermolecular excimer formation, it should be recalled that difficulties may arise from the possible temperature dependence of the excimer lifetime, when effects of temperature on fluidity are investigated. It is then recommended that time-resolved fluorescence experiments are performed. The relevant equations established in Chapter 4 (Eqs 4.43-4.47) must be used after replacing ki[M] by k. ... 

A. Seimiarczuk and W. R. Ware, Temperature dependence of fluorescence lifetime distributions in l,3-di(l-pyrenyl)propane with maximum entropy method, J. Phys. Chem, 93, 7609-7618 (1989). 

Figure 11.12. Temperature dependences of Cr1+ fluorescence lifetime in various host materials. Materials with low strength of crystal field (1) LiSAF (2) LiBAF<44> (3) LiCAF.(44) Materials with high strength of crystal field (4) alexandrite 1 4S (5) ruby (data from 20 to 300K obtained from Nelson and Sturge,(46) (hose from 300K and beyond by the author) (6) emerald.(42)...

The motions of chromophore groups and of their environment that lead to temperature-dependent fluorescence quenching are those on the nanosecond time scale. Slower motions cannot manifest themselves in effects on the excited-state lifetime (this corresponds to the limit of high viscosity). On the other hand, if the motions are considerably faster (on the picosecond time scale), then they should give rise to static quenching. 

The proposed mechanism may explain such excited-state characteristics as the temperature dependence of lifetime or Aex dependence of the fluorescence intensity at low excitation energies. However, in order to explain the energy dependence of the photodecomposition at high energies at least one more dissociative state should be included in the mechanism, which decompose to radicals. 

If this mechanism is indeed correct, then a plot of ln Fo/F - 1 vs 1/T should be linear. Figure 4-,shows that this is indeed the case and that E3 is 19 kJ mol . A more stringent test of the mechanism would, of course, be to determine the dependence of fluorescence lifetime upon temperature such a study is in progress. It is interesting to note that even when a large mole fraction of the cis,trans conformer has been generated by photolysis at a suitable temperature, such a solution exhibits... 

Figure 24. Concentration dependence of the fluorescent lifetime of the Tb 5Z)4 state at various temperatures in Calibo glass [from Ref. (95)].

The temperature dependence of the fluorescent lifetime was also studied. The series of samples which used aluminum oxide as the backup material were selected for these experiments. Figure 24 shows the fluorescence lifetime of terbium as a function of concentration at IT and 4.2°K compared... 

He gives a fluorescent lifetime of about 700 jxscc for the terbium 5D4 state at 77°K. The fluorescence is quenched at room temperature. Unfortunately, the temperature dependence of the fluorescent lifetime was not measured. 

Kondrat eva and Lazeeva (108b) studied the temperature dependence of the fluorescent lifetime of the 5D4 state of terbium sulfate in H20 and... 

It would be extremely interesting to study the temperature dependencies of the fluorescent lifetime of these transitions and also examine the effects of rare earth ion substitution. 

An examination of the temperature dependence of the fluorescent lifetime of both terbium nitrate and europium nitrate in methanol and deuterated methanol was made. There was little change with temperature for either. 

In general, the natural radiative lifetimes of fluorescence and phosphorescence should be independent of temperature. But the emission intensities may vary due to other temperature dependent and competitive rate constants. 

Interesting examples are found in substituted anthracenes. The lifetimes and quantum yields of fluorescence of substituted anthracenes show different dependencies on temperature. The position of the substituent is more important than its nature. For 9- and 9,10-substituted anthracenes, fluorescence quantum yields increase steeply with decrease of temperature, while side-substituted derivatives have low yield and small temperature dependence. The variation is of the form... 

Fluorescence from the Do and Di levels of Eu3+ in doped SrTiOa (cubic perovskite structure) has been observed [618]. The fluorescence decay from the 5Di level consists of radiative transitions to the 7F states and a nonradiative dominant transition to the 5Do level. The decay of the 5X>o state is mainly radiative and is composed of both zero-phonon and phonon-assisted transitions, the latter accounting for much of the temperature dependence of its lifetime. For temperatures upto 300° K, the decrease in the sZ>o lifetime has been correlated [618] with the increased intensity of the vibronic bands [619]. Both 5Z>o 7Fi and 5Do 7F2 transitions as well as 5Di 7F, bD - 7F2 and 5Z>o - 7F show vibronic structures at room temperatures [619] and below. 

At any step during the process, thermal dissipation of energy through vibrational coupling with the solvent or the matrix may bring deactivation of the next step and no / - / fluorescence is then expected. The temperature dependence of the fluorescence yield and the lifetime of several [3-diketonates of Eu3+ have been studied by Bhaumik 631. ... 

TABLE 27 Adiabatic Photolytic Cycloreversion of Lepidoptereue iu Methylcyclohexane/isopentane upon Excitatiou at 274 um. Temperature Dependent Fluorescence Quantum Yields and Lifetimes [134 ... 

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