Angular distribution of laser-induced fluorescence emission of active dyes in scattering media.

Angular dependence of the intensity and the emissive wavelength of the laser-induced fluorescence emission in hybrid media (fluorophores+nanoparticles) are investigated using various TiO2 densities as guest nanoscatterers in the ethanolic solutions of the host Rd6G and coumarin 4 (C4) molecules. It is shown that the intensity of the scattered photons varies in terms of the detection angle. When the nanoscatterer density increases at a certain excitation energy, the angular anisotropy enhances. While the emissive wavelength exhibits the spectral shift in terms of the angular variation for Rd6G fluorophores, it remains invariant for C4-based suspension. In the former case, the emissive wavelength undergoes a spectral shift in terms of angular variation. Several factors such as the optical path length in the scattering media, the excitation volume, and the re-absorption events of the fluorescence emissions by the non-excited molecules strongly affect the spectral features. In fact, the density of the scatterers, the dye concentration, and the interplay between Stokes shift rate and the overlapping between absorption/emission spectra of the given fluorophores are taken into account as the major parameters to form the angular distribution.