Before going into the solutions.

Did you the check the sensitivity of your detector at 785 nm and beyond? What detector are you using?

Here are the solutions you could try

1. Proper choice of wavelength. Fluorescence occurs in a definite wavelength range whereas Raman scattering wavelength changes with excitation wavelength.

2. Identify the cause of fluorescence background and try eliminating it. Sometimes proper choice of the solvent could help. Some solvents give less background and some others give high background.

3. Photobleaching the sample to remove background fluorescence

4. Addition of quenchers. Do it cautiously. There are consequences.

Fluorescence occurs if the virtual energy level overlaps the upper electronic level. Thus, with increasing energy laser (shorter wavelengths) increases the likelihood of fluorescence. it the phenomenon depends on the wavelength of the exciting laser. Therefore, fluorescing at one wavelength, may not fluoresce at other wavelengths. Therefore, when choosing a device, it is very important to take into account how fast and easy it is possible to change the exciting lasers.

See

https://www.sensorprod.com/news/white-papers/2006-05_ser/wp_ser-2006-05.pdf

In publication propose a method for preparation of samples that are applicable to SERS measurements: the ‘‘pressure-attachment’’ method. In this method, analyte powders are spread over SERS active substrate.

Thank you guys But I forgot to tell you more information, Now I'm doing a research about DLC (Diamond Like Carbon) and as I told you that 785 doesn't work because It's not show G-Band Intensity( even if fluorescent is not show too ) and change wavelength to longer wavelength (about 1065 nm) I'm afraid that not have enough energy to excitation of DLC.

then photobleaching I already do it at wavelength 532nm but it just decrease 25% in 10 min (I'll try another wavelength later ) and If you guys have more advice or idea please let me know, I would really appreciate.

The fluorescence background in Raman spectroscopy will reduce when use a longer excitation wavelength. However, the Raman intensity will significantly reduce. I suggest that you should try with wavelength 633 nm. Besides that, you also can try to use a lower percentage energy of wavelength 532 nm laser excitation, and decrease the exposure time.

Could you describe more precise your experiment. Without this information it is very difficult to make suggestions like change the solvent ...

You wrote that you need the solvent. If I have this problem I would measure the absorption of the solvent, and the dissolved agent first. If you have absorption spectra we can try to find conditions with the best Raman-to-fluorescence intensity ratio.

What is the source of the fluorescence you observe: solvent or dissolved agent ?

If you have the resources you could think of time gated detection if it is possible.

No, my sample is solid and maybe what I describe is not clear that I mention about solvent, I mean I don't want any method that use solvent or liquid but thank you for your advice.

I think you can examine two ways:

1- Firstly, take your Raman spectra in a dark room. You must cosider that If your sample is solid( like powder), It's better to make a disk. If not, It's obligue to use another laser with different wavelength( the wavelength should not be in visible region).

2- Secondly, you should subtract the fluorscence from your spectra with some softwares. I don't know what is the type of your sample and I don't see your recorded spectra to guide more and more.

Hi: I agree with Aurelio. If you use a deep UV wavelength (UVC ) then you will probably find that the fluorescence is significantly red-shifted from the excitation line (maybe 10 nm) and that the interesting Raman scattering occurs in the gap between the excitation and fluorescence. You will also get a huge resonance enhancement in cross-section.

See for example:

Erik D. Emmons, Ashish Tripathi, Jason A. Guicheteau, Augustus W. Fountain, III, and Steven D. Christesen, “Ultraviolet Resonance Raman Spectroscopy of Explosives in Solution and the Solid State,” J. Phys. Chem. A 117, 4158-4166 (2013).

Steven D. Christesen, Jay Pendell Jones, Joseph M. Lochner, and Aaron M. Hyre, “Ultraviolet Raman Spectra and Cross-Sections of G-series Nerve Agents,” Appl. Spectrosc. 62(10) 1078-1083 (2008).

L.C. Pacheco-Londono, W. Ortiz-Rivera, O.M. Primera-Pedrozo, S.P. Hernandez-Rivera. ‘‘Vibrational Spectroscopy Standoff Detection of Explosives’’. Anal. Bioanal. Chem. 395(2), 323-335 (2009)

Augustus W. Fountain III, Steven D. Christesen, Raphael P. Moon, Jason A. Guicheteau, and Erik, D. Emmons, “Recent Advances and Remaining Challenges for the Spectroscopic Detection of Explosive Threats,” Appl. Spectrosc. 68(8) 795-811 (2014).

If you want to see an example of a narrow linewidth single peak DUV excitation laser then the following may be of interest. https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9304/93040T/A-six-color-four-laser-mobile-platform-for-multi-spectral/10.1117/12.2077999.short

This is a 250 nm pulsed solid state laser with < 20 GHz linewidth. Best, john

Hi,

Could you please suggest any software to remove raman scattering from fluorescence peak @ Arezou Zarei

i have a same problem, but, mi sample id dark chocolate. Help please!

We have developed a time gated Raman instrument for fluorescence suppression that may be able to provide a solution. The effectiveness depends on the Raman scattering cross section and the lifetime of the fluorescence.

Feel free to contact me for more information.