I am using time correlated single photon counting (TCSPC) to collect TRPL spectra of quantum dots (QDs).

Taking TRPL spectra of solutions is pretty easy in the sense that the excitation passes through the sample and fluorescence can be detected at 90 degrees from the excitation beam without much scattering from the sample. However, for thin films of QDs, avoiding scattering is difficult. Are there any tricks that I can use to collect good TRPL spectra for thin films? I tried manually rotating the sample holder a little bit to change the angle of reflection of excitation beam so that it doesn't go to the detector.

Also, for TCSPC, low concentration of fluorophore is desirable to avoid reabsorption. However, for thin films, the local concentration is very high and therefore I think reabsorption becomes an issue. Is there anyway around that?

Thanks!

Saurabh