Although the spectra look rather simple,
complex samples like crude oil that contain
several absorbing and emitting species actually
have very complex fluorescence emission
spectra. Thus, upon changing the excitation
wavelength, different species can be excited
selectively and the emission spectrum can
change accordingly. In TFS, an excitation
wavelength is selected and the emission is
recorded over the wavelength range of interest.
A new excitation wavelength is chosen and the
emission range is scanned again. TFS data are
thus usually presented as a three-dimensional
map of the fluorescence intensity (z-axis) as a
function of the excitation and emission
wavelengths (x- and y-axes, respectively).
Rayleigh and Raman scattering of the
excitation light by the sample usually result in
artifact signals along two diagonals of the map
(at x=y, corresponding to the coincidence of the
excitation and emission wavelength; and at y =
x + C, where C is determined by the vibrational