Antenna effect in an oxide xerogel

Silica xerogel doped with [Eu subset of cryptand](3+) was prepared by the sol-gel method from a hydrolyzed tetramethoxysilane solution containing [Eu subset of cryptand](CF3SO3)(2)Br. UV-visible optical absorption spectra, fluorescence excitation and emission spectra, fluorescence lifetime as well as luminescence quantum yield were measured. Experiments were carried out in aqueous solution and in rigid silica xerogel at room temperature. It is shown that the excitation is centred on the ligand, but the metal ion takes part in the emission process. In other words, the antenna effect was observed in the Eu(III) cryptate studied in the solution and xerogel. The cryptate entrapped in the xerogel showed higher emission efficiency and longer lifetime than in solution. (C) 1998 Elsevier Science B.V. All rights reserved.