I cannot get the Raman spectrum for carbon based materials like graphene in Raman spectroscopy of 785 nm . What can be done for obtaining the proper Raman peaks for carbon based materials in 785 nm Raman Spectroscopy.
The problem is certainly not the wavelength. In my PhD work, I also used a 785 nm laser to analyze sp2 carbon and it worked fine.
However, if the platelets were very small, occasionally they dropped below the sensitivity of my standard spectrometer because its beam wasn't focussed enough. In these cases, they could only be seen in a confocal Raman microscope.
So, your problem might be the focus of your optics, not the wavelength.
The optical configuration of your system is not quite right,in order to pick up the signals. Although least likely, it is still possible that your materials were not prepared correctly, which has no raman response.