The luminescence of the Ce3+ ion in aqueous solution, which results from d-->f transitions, is observed to be quenched by complexation with multidentate amino carboxylic acid ligands. However, the corresponding complexes containing phosphonic acid moieties show efficient room-temperature luminescence. Luminescence spectroscopy was used to characterize Ce3+ complexes with the following ligands: diethylenetriaminepentakis (methylphosphonic acid) (dtpp), ethylenediaminetetrakis (methylphosphonic acid) (edtp), hexamethylenediaminetetrakis(methylphosphonic acid) (hdtp), and nitrilotris(methylphosphonic acid) (ntp). Complex stoichiometries were determined by monitoring the emission intensity as a function of ligand concentration. The effect of pH on luminescence intensity was examined with quenching noted for higher pH values. Quantum yields of luminescence for each of the complexes were measured using [Ce(H2O)9]3+ as a standard. Energy transfer from Ce3+ to Eu3+ and to Tb3+ was observed to occur in binuclear complexes of dtpp, edtp, and hdtp. Although amino phosphonic acids are potential models for biological phosphate-containing molecules, ATP, tubercidin, and calf thymus DNA were all observed to quench Ce3+ luminescence.
