LUMINESCENCE OF [EU-SUBSET-OF-2.2.1]3+ AND [CE-SUBSET-OF-2.2.1]3+ CRYPTATES ADSORBED ON OXIDE SURFACES

The luminescence properties of the [Eu-subset-of-2.2.1]3+ and [Ce-subset-of-2.2.1]3+ cryptates adsorbed on SiO2 and TiO2 surfaces are reported. There are considerable changes in the excitation and emission spectra of the luminescence of the Eu3+ cryptate compared to those of the complex in aqueous solution. This suggests that H2O molecules in the first coordination sphere of the Eu3+ ion are replaced by Si-O entities. From the long decay time of this complex on silica it follows that there are no H2O molecules coordinating the Eu3+ ion anymore. This suggests that the cryptate molecule has a specific, hemispherical, conformation on this surface. Evidence is given that the [Eu-subset-of-2.2.1]3+ complex decomposes on a TiO2 surface. Since the excitation and emission spectra of [Ce-subset-of-2.2.1]3+ on silica are very similar to those of the complex in aqueous solution and of those of uncomplexed Ce3+ ions on silica, no conclusions about the differences in the coordination of the Ce3+ ion in these surroundings can be drawn based on our measurements.