Two-Dimensional Photoluminescence Behavior of Langmuir-Blodgett Monolayers and Multilayers Composed of Decatungstoeuropate

Abstract

Decatungstoeuropate/dimethyldioctadecylammonium (EuW10/DODA) Langmuir-Blodgett (LB) monolayers and multilayers (7 layers) were fabricated by using aqueous solution of EuW10 with different concentration (1.0–3.0 μmol dm−3). The results of specular X-ray reflectivity (SXR) and grazing incidence X-ray diffraction (GIXD) measurements for the EuW10/DODA LB films indicated an increase in the interlayer distance and in-plane molecular ordering for the film fabricated with the concentrated EuW10 solution, reflecting the dense packing of DODA and EuW10 molecules. Their photoluminescence property also depended on the concentration of the EuW10 solution. With an increase in the EuW10 concentration in the subphase, both the relative intensity of the 5D0→7F1 transition and the emission lifetime increased. The lifetime of emission of the EuW10 LB monolayers changed from 0.8±0.1 ms (1.0 μmol dm−3) to 1.0±0.1 ms (2.1 μmol dm−3) and 1.3±0.1 ms (3.0 μmol dm−3), which became closer to that (2.6 ms) of the solid, and EuW10/DODA LB multilayers had the same tendency. The elongation of the emission lifetime was due to a decrease in the number of aqua molecules within the Eu3+-coordination sphere, which will be caused by the dense and regular packing of EuW10 molecules.