I checked time-resolved photo luminescence(TRPL) for CsSnBr3 perovskites thin films (emission wavelength: 693nm, excitation wavelength: 465nm) .

But, I observed two peaks which are not expected.

Usually, it should be exponentially decayed, but a strange phenomenon was found and it rose and fell again.

What is the origin of it? Could it be that I have set the parameters wrong?

I upload the graph and parameters for TRPL.