I'm doing fluorescence spectroscopy on my protein expecting to see the intrinsic fluorescence of tyrosine and also its effect with addition of cu(i). The excitation wavelength was 280 nm while the emission wavelength were from 300-500nm. From my reading, it supposed that tyrosine will have an emission peak at 307nm. However, in my case, an emission peak appeared at 380nm. None at 307nm. What can that be? Is it still tyrosine or something else? My protein is in MOPS buffer pH 7.