Spectroscopic behavior of hybrid materials obtained by the sol-gel technique

The need for new, chemically and physically stable luminescent materials operating with UV excitations has stimulated research on luminescence properties of doped sol-gel material. In this work we present technology of production of silica gels doped with organic molecules, lanthanide compounds and organic/inorganic composites. Optical properties of these materials as functions of temperature, concentration and excitation wavelength are presented. Dynamics of the excited states is discussed based on the decay times and emission efficiencies data. Mechanisms of ligand-to-metal energy transfer as well as other processes affecting emission efficiency are considered. Silica sol-gels doped with di-aminoacid derivatives of porphyrins: PP(Ser)(2)(Arg)(2), PP(Ala)(2)(Arg)(2), PP(Met)(2)(Arg)(2), where Met, Arg and Ser denote methionine, serine and arginine aminoacids, respectively, and H2TTMePP {tetrakis[4-(trimethylammonio)phenyl]-21H,23H-porphine} have been obtained and spectroscopically studied. The samples emit only from the lowest excited singlet state (S-1). Intensity of this emission depends on the concentration of the active molecule and time of the exposition to the excitation beam. The sample containing PP(Ser)(2) (Arg)(2) co-doped with Tb(III) ions exhibits only D-5(4) emission from the metal center. When co-doped with Pr(III) ions it displays only the S-1 emission and it has been shown that the metal ions affect the S-2 --> S-1 internal conversion. These materials can find applications as phosphors or sensors of UV irradiation. The efforts have been undertaken also to obtain chiral anisotropic materials. (C) 2003 Elsevier B.V. All rights reserved.