I personally operate a confocal Raman spectrometer and go through such problems every now and then.

Your material has some luminescent properties in optical range and that is the problem. Raman peaks very often have very small intensity compared to other spectroscopic techniques. If your samples give some prominent PL emission, then the associated photon-intensity covers completely the Raman modes, and you get a useless large hump through out the range.

Solution: There is not a single solution to completely get rid of it, but you may follow a number of precautions that work in 90% cases.

1. Experiments must be done in fully dark conditions. No other light source should be there except the laser itself.

2. Try to look for data with minimum possible laser intensity. Generally, the problem comes vigorously only after a certain (threshold) laser power.

3. Focus the laser spot to a small patch of sample, preferably a rough surface.

4. Vary (x,y,z) and position of laser spot along with laser power and look if anywhere some Raman peaks are visible. This may take some time.

5. Finally, if you get the peaks, do quite a bit slow scan to obtain some publishable data.

However sometimes, unusual reflectance or scattering of the incident light also becomes problematic in absence of fluorescence or luminescence. But, the precautions are the same for that too.

I personally operate a confocal Raman spectrometer and go through such problems every now and then.

Your material has some luminescent properties in optical range and that is the problem. Raman peaks very often have very small intensity compared to other spectroscopic techniques. If your samples give some prominent PL emission, then the associated photon-intensity covers completely the Raman modes, and you get a useless large hump through out the range.

Solution: There is not a single solution to completely get rid of it, but you may follow a number of precautions that work in 90% cases.

1. Experiments must be done in fully dark conditions. No other light source should be there except the laser itself.

2. Try to look for data with minimum possible laser intensity. Generally, the problem comes vigorously only after a certain (threshold) laser power.

3. Focus the laser spot to a small patch of sample, preferably a rough surface.

4. Vary (x,y,z) and position of laser spot along with laser power and look if anywhere some Raman peaks are visible. This may take some time.

5. Finally, if you get the peaks, do quite a bit slow scan to obtain some publishable data.

However sometimes, unusual reflectance or scattering of the incident light also becomes problematic in absence of fluorescence or luminescence. But, the precautions are the same for that too.

Thank you Souvik Bhattacharjee :)

This background is not necessarily luminescence, but can often be due to scattering from powders. One solution is to compress the powders into a pellet, as is normally done for KBr in IR spectroscopy.

Changing the excitation wavelength ( if your system have such option) may be a solution to avoid the PL problem. Use higher wavelength excitation than your PL emission wavelength.

TiO2 should not absorb or emit at visible wavelengths. See this example of background due to scattering in Raman and how to alleviate it:

"In vitro analysis of immersed human tissues by Raman microspectroscopy", F. Bonnier, A.Mehmood, P. Knief, A. Meade, W. Hornebeck, H. Lambkin, K. Flynn, V. McDonagh, C. Healy,T.C. Lee, F.M. Lyng, H.J. Byrne, Journal of Raman Spectroscopy, 42, 888–896(2011)

Thank you so much all of you! My problem is solved. Slow scan at 1p instead of 5 and 10p and lessening the range did the trick. Thanku all for your help.