Luminescence Kinetics Deconvolution

The decay of phosphorescence emissions can be observed easily with conventional flash photolysis instruments, since they last between ms and seconds. However, fluorescence lifetimes are of the order of ns and such kinetics can be measured only by laser flash photolysis or by time-resolved single photon counting. 

A multichannel analyser is a type of digital x—y recorder in which x is the channel number (in this case the time after the excitation pulse) and y is the number of events which occur for the relevant channel (in this case the detection of a photon). For each excitation pulse the first emitted photon only is counted, but as the experiment is repeated many times with excitation pulse trains of thousands per second the whole kinetics of luminescence is reconstructed. 

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Deconvolution. When the luminescence lifetime is close to the laser pulse duration, the kinetics can still be obtained by a process known as deconvolution, so long as the luminescence decay is exponential. The deconvolution program is a computer simulation of the shape of the laser pulse modified for various luminescence lifetimes. An example is given in Figure 7.33. The kinetics of fluorescence decay could not be resolved directly, but it is clear that the emission pulse shape differs from the laser pulse shape... 

Typically, in measurements of time-resolved luminescence in the time regime of tens of picoseconds, data obtained from 10 to 20 laser shots are averaged to improve the signal-to-noise ratio and to minimize the effects of shot-to-shot variations in the laser pulse energy and shape. Once the reliability of the data has been ensured by application of the corrections described above and made necessary by detector-induced distortions, the time-resolved fluorescence data is analyzed in terms of a kinetic model which assumes that the emitting state is formed with a risetime, xR, and a decay time, Tp. Deconvolution of the excitation pulse from the observed molecular fluorescence is performed numerically. The shape of the excitation pulse to be removed from the streak camera data is assumed to be the same as the prepulse shape, and therefore the prepulse is generally used for the deconvolution procedure. Figure 6 illustrates the quality of the fit of the time-dependent fluorescence data which can be achieved. 

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