How does one obtain fluorescent spectra for nanodiamond suspensions in a standard fluorimeter?
The high refractive index of diamond causes a substantial amount of light scattering, which can significantly affect the emission spectral profile. Moreover, scattering is maximized at 90 degrees, and it is minimized at 180 degrees. Collecting emitting light at 90 degrees relative to the excitation is pretty standard in most instruments and this obscures spectra collection. Thus, regarding the emission spectra, it is more of an instrument/measurement geometry issue. A measurement angle of 90 degrees typically will not work well with diamond without some additional modifications. We obtained a recommendation for measurements with our Horiba instrument to overcome high light scattering by nanodiamonds: “It proved quite easy to drop the background scatter by using a Fluorolog3 with two double grating monochromators.”
For obtaining emission spectra in our set up, we use a 532 nm laser excitation which is fed into an epifluorescent microscope. In this setup, the collection angle (relative to the excitation line) is at 180 degrees.