Concentration of hypericin was150 nM in 1% DMSO solution (v/v). Excitation wavelength 550 nm, emission observed in range 575-700 nm.
Can you please give some more information?
When and how many times did you repeat the experiment? How much increase do you observe (show us the absorption and emission spectra)? Did you repeat the experiment with the same sample or the experiment is repeated afresh?
Increase in intensity may be an artefact. Rule our the artefacts first.
1. Check if there are any suspended particles. They could cause scattering and can cause an increase in the signal. Filter the solvent before using, if required.
2. Check if Raman scatter overlaps with your sample emission and see if this could cause the increase. Shifting the excitation wavelength will cause the emission peak to shift, in case of Raman scatter.
3. Increase the integration time and record the fluorescence signal and see if you still see the variation.
4. Stray light leaking to the detector etc
If required record the emission spectra. All the above artefacts give rise to sharp features in your spectra.
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