Fabrication of photoluminescent multibilayer composite films consisting of a rare-earth-containing polyoxometalate Na9[EuW10O36] and dimethyldioctadecylammonium chloride

Photoluminescent multibilayer composite films consisting of a rare-earth-containing polyoxometalate (POM) Na-9[EuW10O36] (EuW10) and dimethyldioctadecylammonium chloride (DODA) have been prepared by the ion-exchange method and characterized by UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ellipsometry, scanning electron microscopy (SEM) and fluorescence spectroscopy. UV-Vis spectra show that the content of EuW10 in the composite films increases with the exchange time and become constant after 13 days exchange. Moreover, the exchange between the Cl- ions and the EuW10 polyanions is purely kinetically controlled and goes to completion after more than 10 days exchange, which is also confirmed by XPS. XRD patterns and ellipsometric measurements give the periodicity of ca. 45.5 Angstrom and total film thickness of 566 +/- 8 Angstrom for the ion-exchanged film, indicating that the composite film contains about 12 multibilayers of DODA/EuW10/DODA. Scanning electron micrograph provides the morphology of the composite film and shows that the film surface is relatively homogenous and consists of a large number of closely packing microcrystals formed by EuW10 and DODA. The photoluminescent properties of the composite film determined by fluorescence spectroscopy are similar to those found for the EuW10 solid. (C) 2002 Elsevier Science B.V. All rights reserved.