Average decay time

When the fluorescence decay of a fluorophore is multi-exponential, the natural way of defining an average decay time (or lifetime) is ... 

In this definition, each decay time is weighted by the corresponding fractional intensity. This average is called the intensity-averaged decay time (or lifetime). 

The definition used depends on the phenomenon under study. For instance, the intensity-averaged lifetime must be used for the calculation of an average colli-sional quenching constant, whereas in resonance energy transfer experiments, the amplitude-averaged decay time or lifetime must be used for the calculation of energy transfer efficiency (see Section 9.2.1). 

Transfer efficiency can be calculated by using the average decay times of the donor in the absence and presence of acceptor, as follows ... 

For the calculation of transfer efficiency, it is incorrect to use the intensity-averaged decay time (see Section 6.2.1 for... 

The result of a number of curve fits are averaged to further reduce the effects of noise. The averaged decay time is then compared with values stored in adigital look-up table to determine the temperature of the sensor. 

Under condition of a fast thermalization between the three triplet substates, one can derive a simple expression for the resulting decay time that represents an average decay time (e.g. see the Refs. [105-107]) ... 

In order to avoid bias due to number fluctuations, it is necessary that there is at least 1000 particles present in the measuring volume and, for a typical value of the scattering volume of 10 cm, effects of number fluctuations are to be expected for particle diameters greater than around 0.5 pm. Number fluctuations lead to an additional time decaying term in the autocorrelation function. Since the characteristic decay time of this additional term is usually much slower than the decay attributed to Brownian motion, the average particle size, which is proportional to the average decay time, will be overestimated if the effect of number fluctuations is neglected [277]. 

As an example of excitation energy transfer studied by time-resolved fluorescence, let us take again the case of the inclusion complex of the multichromophoric cyclodextrin CD-St with oxazine 725 described in Section 7.2.4.2 [15]. Figure 7.9 shows the fluorescence decay of CD-St the very first part of the decay is due to energy transfer [13] from the steroidic naphthalene fluorophores to oxazine 725. Data analysis led to an average decay time for transfer of about 25 ps, which is quite fast, as expected from the short average distance between donor and acceptor ( 9-10 A). 

Average Decay Times. De Mayo and Ware have treated the monomer and excimer fluorescence decays of Py on dry and modified silica as being double-exponential, see Table 1. It was pointed out, however, that this was only an approximate representation of the decays and that no precise physical significance was intended to be associated with the derived parameters and A (30), see [3] and [4]. In order to be able to use these data in discussions... 

Determination of distances at a supramolecular level using RET 2S3 where the amplitude-averaged decay times are defined as ... 

Cycle time Average, decay time Water activity... 

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