Eu3+ coordination in an organic/inorganic hybrid matrix with methyl end-capped short polyether chains
Journal article, 2005
Fourier Transform mid-infrared (FT-IR), Fourier Transform Raman (FT-Raman) and photoluminescence spectroscopies and Two-Dimensional (2D) Correlation Spectroscopic Analysis were employed to examine the anionic and cationic local environments in mono-urethanesils doped with europium triflate (Eu(CF 3-SO3)3). The hybrid host framework of these materials is composed of a siliceous backbone bonded through urethane linkages to CH3-terminated polymer chains containing about 7 OCH 2CH2 units. Samples with ∞ ≥ n (composition) ≥5 (where n = OCH2CH2/Eu3+) were studied. In terms of ionic association, the level of complexity of these xerogels is very high. In all the compounds the triflate ions exist "free", weakly coordinated and forming cross-link separated ion pairs. At 20 ≥ n ≥ 5, in addition to all these species contact ion pairs occur. In agreement with these conclusions, photoluminescence establishes the presence of three distinct cation local sites (Eu3+/O=C(urethane cross-links), Eu3+/O-C- C(polyether chains) and weakly coordinated Eu3+/CF3SO 3- ionic pairs).