Rare earth doped mesoporous hybrid thin films with tunable optical responses

Abstract

Optical quality mesostructured silica thin films functionalized with three large hydrophobic organosilylated quinizarin derivatives are prepared via evaporation induced self-assembly (EISA). Incorporation of Eu³⁺ is performed by post-reacting the functionalized layers with several europium precursors. Unambiguous location of the quinizarin moieties inside the porosity and their accessibility to Eu³⁺ ions are demonstrated using XRD, SAXS and fluorescence measurements. Complexation of Eu³⁺ reduces the fluorescence of quinizarin; for some europium precursors an energy transfer between the grafted organic dye and the lanthanide is clearly observed. The luminescence intensity of Eu³⁺ can be tuned by varying the nature of the rare earth precursor, the mesophase and the chelate itself. The resulting optical responses differ with respect to concentration, lifetime and local environment of Eu³⁺ inside the thin films. Additionally, efficient energy transfer from Tb³⁺ to Eu³⁺ and electronic coupling probed by EPR between Cu²⁺ cations trapped in such mesoporous hybrid films give strong evidence of the presence of several metal ions per pore.