Prof. Gnatenko

This is not my field, but if you don't mind I would like to contribute my 2 cents' worth.

Normal fluorescence spectroscopy is useful as a highly selective and sensitive non-invasive probe. However, better chemical information can often be gained from the same experiment by exploiting the time-dependent nature of fluorescence.

Time-resolved fluorescence provides more information about the molecular environment of the fluorophore than steady-state fluorescence measurements. Since the fluorescence lifetime of a molecule is very sensitive to its molecular environment, measurement of the fluorescence lifetime(s) reveals much about the state of the fluorophore. Many macromolecular events, such as rotational diffusion, resonance-energy transfer, and dynamic quenching, occur on the same time scale as the fluorescence decay. Thus, time-resolved fluorescence spectroscopy can be used to investigate these processes and gain insight into the chemical surroundings of the fluorophore.

As far as I know time resolved fluorescence is also used in chemical kinetics.

1) in usual PL it can be difficult to attribute spectral maxima to the particular transitions, especially in novel, not very known and pure materials. In this case time-resolved PL just provides additional information, which makes easier to distinguish between, for example, exciton and e-A0, D0-A0 and so on, since they have different life-times.

Also, additional information can be obtained via magneto-PL studies, etc.

2) Time resolved PL may be useful to study basic intersubband phenomena in QDs and QWs. For example, you can study intersubband dynamics using visible-light spectroscopy, which is much easy than IR, where usually intesubband energies lie.

Basically it gives you the carrier lifetime, or lifetimes of different recombination processes. Depending on the functional dependence on time it gives information on the recombination mechanism(s), and by looking if the time response depends on emission wavelength you can more reliably attribute different PL bands to different processes.

On a more basic level, lifetimes are an easier method to compare samples than PL intensity because it is not affected by changes in the setup and laser intensity (ok, some recombination is injection-dependent), misalignment of the sample, etc.