Enhanced Eu3+ Emission in Aqueous Phosphotungstate Colloidal Systems: Stabilization of Polyoxometalate Nanostructures

• Published in: Langmuir Vol. 26; no. 17; pp. 14170 - 14176
• Main Authors: Barbosa, A. J, Maia, L. J. Q, Montanari, B, Gonçalves, R. R, Messaddeq, Y, Ferreira, R. A. S, Carlos, L. D, Ribeiro, S. J. L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07-09-2010
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Water; Modification; Nanoparticle; Stabilization; Metal ion; Phosphate group; Nanostructure; Tungstates; Polyphosphates; Colloid; Transmission electron microscopy; Efficiency; Aqueous medium; Structure
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la100525h

Luminescent Eu3+-containing polyphosphate−tungstate aqueous colloidal systems were prepared and studied as a function of the relative polyphosphate−tungstate content. In polyphosphate-rich solutions, Eu3+ ions occupy cagelike sites composed of phosphate groups from the metaphosphate chains. In these sites, an average number of 0.5 water molecule coordinates to an Eu3+ ion and the 5D0 emission quantum efficiency is 0.22. Tungstate addition leads to important modifications in neighboring Eu3+ leading to coordination sites in the aqueous medium where metal ions are completely hidden from interactions with solvent molecules. Transmission electron microscopy results clearly show W-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstate relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu3+ in polyoxometalate (POM)-like sites by comparison with the well-known decatungstoeuropate [EuW10O36]9− structure. These new aqueous colloids display surprisingly high 5D0 emission quantum efficiencies of ca 80% because of the strong ligand field provided by tungstate POM ligands and the complete absence of water molecules from the Eu3+ first coordination shell.