Raman Signal is really weak at wavelength such as 400 nm, 514 nm and 785 nm for my samples containing fluorescent nanoparticles. I want to know the D band and G band of carbon domains in my sample but due to fluorescence, it was impossible. 1064 nm is an option but I need to understand why some literature measures Raman signal @514 nm even though they have fluorescent nanoparticles also.
Why other people can measure using 514 nm excitation, that mostly depends on particular samples - the luminescence can differ by several orders of magnitude even for similar samples.
Still, there are couple of tricks that might help you measure your sample: If the luminescence is not to big, try to subtract it using a software tool (kindaArticle Complex evaluation of Raman spectra using morphological filt...
), the peak might show up satisfactorily. If the luminescence is to high, try to lower it first. To this end, you can use high power laser and high NA objective (up to values that yet do not burn your sample) and apply bleaching - if you continue to shine on the sample, the luminescence will go down with time. If the luminescence becomes so high that it saturates the detector, you can try to add an ND filter in the detection path of the spectrometer (ie. keep excitation high to have bleaching + attenuate only the outgoing light somewhere behind the Raman filters).Apart that, you can try polarized Raman (Article Direct Measurement of Resonance Raman Spectra and Cross Sect...
), or a chopper to mechanically decrease the fraction of luminescence going to the detector. Last but not least, a metallic surface (sputtering a thin layer over your sample - if feasible) might quench the luminescence greatly.- Badges
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