Preparation and luminescence properties of hybrid materials containing lanthanide complexes covalently bonded to a terpyridine-functionalized silica matrix

New kinds of organic-inorganic hybrid materials consisting of lanthanide (Er³⁺, Eu³⁺, and Tb³⁺) complexes covalently bonded to a silica-based network have been obtained by a sol-gel approach. A new versatile compound containing terpyridine has been synthesized by 4′-p-aminophenyl-2,2′:6′,2″-terpyridine and 3-(triethoxysilyl)propyl isocyanate, which is used as the a ligand of lanthanide ions and also the siloxane network precursor. The obtained hybrid materials were characterized by FT-IR, TGA, DSC, near-infrared, and visible spectrofluorometer, as well as decay analysis. For the Hybrid-Er and Hybrid-Eu, excitation at the ligand absorption wavelength resulted in the typical near-IR luminescence (centered at around 1.54 μm) resulting from the ⁴I_13/2-⁴I_15/2 transition of Er³⁺ ions and strong visible region emission of the Eu³⁺ ions (⁵D₀-⁷F_J), which contributed to the efficient energy transfer from the ligands to the lanthanide ions. However, we have not found strong emission for the Hybrid-Tb. This indicated that the energy transfer did not take place in this system. A model of indirect excitation mechanism to explain the phenomenon was also suggested.