As far as I understand both of these techniques are based upon exciting the samples and collecting the emission spectra. In Pl measurement, a sample is photoexcited and if the energy is above the bandgap, the emitted photons are collected and analyzed however in the TA measurement a pump is used to excite the sample and the probe monitors the relaxation dynamics. It basically gives information about the relaxation dynamics. If it is correct, then what is the significance of using one technique over others?
Hi Bibek
I will try to answer as best as I can. Indeed, both techniques as you commented give information about the relaxation dynamics from the excited state.
1-In PL you are basically collecting photons spontaneously emitted by the sample (fluorescence), thus to collect the signal you only need to excite the sample.
Therefore you study the relaxation dynamics from fluorescent excited states.
2- On the contrary in TA measurements the photons you collect are not directly emitted by the sample. You basically start the experiment in the same way, exciting your sample with a laser (pump) and then you follow the changes in absorption with another light pulse (probe). Thus in these measurements you study all types of excited states that your sample has, those fluorescent and non fluorescents.
Therefore if your sample is fluorescent, PL and TA techniques will give you similar results, although you might have extra decay times in TA from non fluorescent excited states. On the contrary if your sample is non-fluorescent you can only use TA to study the excited state dynamics.
The main technique for PL is TCSP (time correlated single photon counting), where you can get around 4-10 ps time resolution and good decay times until several ns, for shorter times you should do fluorescent upconversion, and longer follow the emission with for example PM and an oscilloscope. For TA the simple approach is to follow UV-vis changes, and generally you have time resolutions of around 100 fs to 2-3 ns with an optical delay line. For longer time scales you need to do flash-photolysis 10 ns to ms.
Experimentally, I consider PL is much easier than TA (for decay times longer than a few hundreds of ps) thus if you have a fluorescent sample Pl should be enough to characterize.
Cheers
Lucas
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