Photobleaching as a useful technique in reducing of fluorescence in Raman spectra of blue automobile paint samples

• The usefulness of photobleaching pre-treatment as a method, which could reduce or quench fluorescence that precluded identification of pigments, was described.
• The influence of parameters like time of irradiation, laser power and the type of paint on the obtained results was checked.
• The photobleaching enabled us to identify pigments in 90% of examined samples.

The usefulness of the photo-beaching technique in reducing the fluorescence background in Raman spectra of automotive paints was studied. The method was applied to group of 20 blue solid and metallic paints, in which pigment identification with the use of a green laser (514.5 nm) was not possible due to strong fluorescence. The samples were irradiated by high laser power for a long period of time before acquiring spectra. The process of bleaching was studied in detail based on two samples. Then the procedure was applied to all samples before acquiring spectra. Due to irradiation fluorescence originating from the background decreased, whereas Raman scattering features of samples stayed unchanged. The applied procedure satisfactorily quenched fluorescence in 90% of examined samples and made pigment identification possible.