Otro
Enhanced Eu3+ Emission in Aqueous Phosphotungstate Colloidal Systems: Stabilization of Polyoxometalate Nanostructures
Registro en:
Langmuir. Washington: Amer Chemical Soc, v. 26, n. 17, p. 14170-14176, 2010.
0743-7463
10.1021/la100525h
WOS:000281354000062
Autor
Barbosa, A. J.
Maia, L. J. Q.
Montanari, B.
Goncalves, R. R.
Messaddeq, Younes
Ferreira, R. A. S.
Carlos, L. D.
Ribeiro, Sidney José Lima
Resumen
Luminescent Eu3+-containing polyphosphate tungstate aqueous colloidal systems were prgared and studied as a function of the relative polyphosphate tungstate content. In polyphosphate-rich solutions, Eu-H- 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 500 emission quantum efficiency is 0.22. Tungstatc 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 \V-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstatc relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu34- in polyoxometalate (P0M)-like sites by comparison with the well-known decatungstoeuropate [EuW10O36](9-) structure. These new aqueous colloids display surprisingly high 5llo 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.