The fluorescence of Eu3+ in certain Eu3+-aromatic acid complexes were
enhanced by over two orders of magnitude, by the addition of La3+; a p
rocess referred to as cofluorescence. Cofluorescence was observed only
with certain aromatic acid ligands; trismesic acid, pyromellitic acid
and mellitic acid; thereby clearly establishing a correlation between
the structure of the ligand and the process of cofluorescence. While
cofluorescence has been extensively studied using beta-diketones as li
gands, our studies demonstrate cofluorescence for the first time in li
gands other than beta-diketones. Furthermore, the mechanism of cofluor
escence in the aromatic acid complexes studied by us appears to be dif
ferent from that operating in the beta-diketones. While intermolecular
energy transfer is believed to occur in the beta-diketones, formation
of polynuclear complexes appears to be responsible for cofluorescence
in the aromatic acid ligands. (C) 1997 Elsevier Science B.V.