HI, fluorescence is emitted radiation from an electronically excited singlet state where the excited electron in the LUMO has a spin opposite to the remaining electron in the HOMO. Therefore it can relax without spin change and the lifetime of the excited state is typically in the range of ns.

Phosphorescence is emitted radiation from an electronically excited triplet state where the excited electron in the LUMO has athe same spin as the remaining electron in the HOMO. Therefore a spin flip os necessary for relaxation and the lifetime of the excited state is longer, typically µs to ms.

I guess the two modes are well described in the guide or help function of your spectroscopic setup. However possibly for phosphorescence the integration time is longer by default as the signal appears over longer time after single excitations and is much weaker.

If you expect triplet states in your sample youh should work in the phosphorescence mode - if you have bright visible fluorescence occuring from excited singlet states go to fluorescence.

thank you Sir @ Franz-Josef Schmitt

Now if im correct i can check for the visible fluorescence through UV-visible spectroscopy right?

I think that does not help, because UV/Vis is generally absorption spectroscopy which does not tell you much about fluorescence or phosphorescence.

I would measure in fluorescence mode and only switch to phosphorescence mode if you have reason to assume that your sample forms a lot of tripletts. But I guess in both cases (fluorescence and phosphorescence) you will see good spectra of luminescence just it would maybe be optimized for the phosphorescence signal if you measure phosphorescence in phosphorescence mode.

Yes, sir that is very much of a case with me. The sample im dealing with is showing both fluorescence and phosphorescence spectra with peaks at same wavelengths, just that the peaks are little broader (definitely not optimized) in case of phosphorescence. Now im a bit of a confuse which spectra to take to proceed further with my work as the literature review suggest that my sample is capable of showing both fluorescence and phosphorescence spectra.

If you do not especially need to refer to the phosphorescence I would take the fluorescence mode and clearly describe the situation and settings chosen on the spectrometer

Sir, is there any particular reason for preferring the fluorescence mode

hello,

If you want to deal with primarily the emission spectra, then do fluorescence as it will give you real time overall spectra. On the other hand, if you took phosphorescence spectra, then you will start losing the emission with little lifetime and you will be only left with longer lifetime components. In phosphorescence mode, the detector becomes activated after some delay (set by you) and of course, the light source here will be pulsed. But, in fluorescence, light source is continuous and detector is always on..

thank you Sir, Saptarshi Pal

Also if you could recommend a book or review relating PL spectroscopy that will be a great help.

thanks.

It depends on your topic. I am mainly working on PL emission originating from the defects of solids. Now, if you are working on organic molecules, then the scope will be different. Therefore, I would like to suggest you to find out a review or book based on your focused interest. However, you can see the book titled "LUMINESCENCE from theory to applications" edited by Cees Ronda (Wiley).