The self-absorption phenomenon in quantitative Raman spectroscopy and how to correct its effects

Abstract

When the wavelength of the Raman scattered light coincides with the absorption spectrum of the sample, a phenomenon known as Raman self-absorption occurs. If the absorption wavelength range matches completely with the Raman wavenumber range for a given excitation line (high absorption), this process causes spectra with poor signal-to-noise-ratio, making the acquisition nearly impossible. When the absorption of the sample and the Raman scattered are partially coincident (low absorption), smaller modifications in the band-profile of the Raman spectrum are expected difficult to be detected. If a different excitation wavelength is available in order to avoid or minimize this phenomenon, a correction method is customary. The correction methods developed so far in quantitative analysis are still very complex and require the knowledge of several sampling parameters. In this work, we present a very simple but reliable method based on the Beer-Lambert law to correct low self-absorption effects. This method uses simple concepts, a straightforward methodology and the concentration of the Raman active component in the liquid matrix is the only parameter required to perform the correction. This method may be extremely useful in different fields in which Raman spectroscopy is used to obtain molecular and structural information from a band profile analysis. As an example, the method is applied here to successfully correct the Raman spectra of different CuSO4 aqueous solutions excited at 532nm.