Hi,
I could see a peak around ~330 nm for the water sample (MilliQ). This looks strange and I am unable to find the problem. The excitation was 295 nm. We washed the cuvette throughly, but still can see the peak at 330 nm. It would be a great help if someone can assist us in finding the problems and/or the attached results.
Best,
Bikash
That is Raman scattering. Change the excitation wavelength to confirm it. Notice that the full width at half maxima (FWHM) of 295 nm signal (Rayleigh scattering) and 330 nm signal (Raman) are similar. Small FWHM of ~10 nm is indication of scattering. See previous discussions on Raman scattering. It is also a good scientific practice to record spectra from excitation wavelength+10 nm.
https://www.researchgate.net/post/PLphotoluminescence_signal_produced_by_DI_water
It's probably the Raman scattering peak of water. If so, when you change the excitation wavelength, the peak emission wavelength will also change. This will not happen for a fluorophore contaminant.
There is no way to avoid this peak - it is an inherent property of the solvent. You just have to subtract it from the spectrum of your fluorophore.
That is Raman scattering. Change the excitation wavelength to confirm it. Notice that the full width at half maxima (FWHM) of 295 nm signal (Rayleigh scattering) and 330 nm signal (Raman) are similar. Small FWHM of ~10 nm is indication of scattering. See previous discussions on Raman scattering. It is also a good scientific practice to record spectra from excitation wavelength+10 nm.
https://www.researchgate.net/post/PLphotoluminescence_signal_produced_by_DI_water
Thanks Dr. Adam and Tuhin. Yes, I verified the shifting of the peak by changing the excitation wavelength.
When you record the fluorescence spectra, you should select the range starting a few nm after the excitation wavelength. I mistook the first peak for Raman scattering, which was actually the excitation light. The second peak in your spectra is indeed the Raman scattering signal.
Hi,
The water Raman peak is also used to check the health of the instrument. Horiba provides a manual, which shows the expected Raman Intensity for a new instrument. As the Xenon arc lamp becomes older the Raman intensity decreases. Depending on the Raman profile one could determine the time to change the lamp.
As tuhin mentioned it's a very good practise to check the water Raman profile before starting experiments. It helps to keep updated information of instrumental uncertainty obtained due to aging and mishandeling.
Thnaks
Raman scattering peak wavelength can be easily predicted: transform excitation wavelength in cm-1 (295 nm correspond to 33898 cm-1); subtract 3600 cm-1 (the OH stretch vibrational frequency): 30298 cm-1; transform this into wavelength: 330 nm.
@Ming: please note that the Raman signal is not from the excitation source, but from the solvent...
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