The fluorescence of suspensions of powdered coals

The fluorescence spectra of aqueous suspensions of powders of polystyrene, two phenol-formaldehyde resites and a humic acid have been shown to be similar to the fluorescence spectra of their solutions in polar solvents. Fluorescence occurs both from individual aromatic structures and from excimers caged in the solid powders. Accordingly, the synchronous fluorescence (Delta = 20 nm) of aqueous suspensions of a range of powdered coals showed the majority of the aromatic structures present in the coals to consist of substituted mono- and bi-aromatic rings. Excimers and exciplexes were also present. Excitation spectra of the aqueous suspensions confirm this interpretation, The fluorescence of powdered coals suspended in chloroform arises from the material extracted into the solvent. Accordingly the fluorescence spectra are dominated by the excimers and exciplexes formed in the solution; this fluorescence is enhanced by energy transfer from the smaller aromatic systems. (c) 2005 Elsevier Ltd. All rights reserved.