abstract
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.
keywords
SURFACTANT-ENCAPSULATED POLYOXOMETALATE; INTRAMOLECULAR ENERGY-TRANSFER; LANGMUIR-BLODGETT-FILMS; POLY(CARBOXYLIC ACIDS); LANTHANIDE COMPOUNDS; LOCAL COORDINATION; CRYSTAL-GROWTH; PECHINI METHOD; LUMINESCENCE; COMPLEXES
subject category
Chemistry; Materials Science
authors
Barbosa, AJ; Maia, LJQ; Montanari, B; Goncalves, RR; Messaddeq, Y; Ferreira, RAS; Carlos, LD; Ribeiro, SJL
our authors
Luís Carlos
Full professor