Singlet and radiative lifetime

If one excites a sample with an infinitely narrow pulse of hght creating a population of excited singlet state molecules M(Sj), one can write a differential equation that relates the concentration of M(Sj) at any time, t, to the various deactivation processes  

Thus if the only deactivation process of Si was fluorescence then tj = tr, and F = 1. An important relationship is  

When one measures ts and 4 f then the intrinsic molecular rate constant, kR = Tr, can be calculated. 

The above section has outlined the physical parameters that describe the fluorescence process. One can measure the fluorescence spectrum, P(X), the singlet excited state lifetime, xs, and determine the Tliese parameters can be interpreted in terms of the structure, environment and ( mamics of the molecule of interest. In this section, the different optical and electronic components comprising an instrument that can measure Fl( ) and will be described. This instrument is generally known as a steady state fluorescence spectrometer, since it integrates the fluorescence intensity over a given time period. Time-resolved fluorescence instrumentation that is used to measure the excited singlet state decay times is described in Chapter 3. 

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