Polyoxometalates luminescence

In acetonitrile solution the luminescence of [Eu(H20)4(o i-P2Wi706i)]7 increases with the addition of 1,10-phenanthroline or 2,2-bipyridine and reaches a limiting value with a 2 1 ratio of the bidentate ligand to polyoxometalate complex, consistent with the replacement of the four aqua ligands of the Eu cation (Boglio et al., 2006). 

Interest in polyoxometalate complexes of the rare earths has been driven to a large extent by their photophysical and photochemical properties. Table 1 lists several reviews. In general, photoexcitation into LMCT (O -> W, O -> Mo) bands results in intramolecular energy transfer to the rare earth with subsequent emission and luminescence. 

Polyoxometalates are important reagents in analytical chemistry and they also find applications in catalysis, molecular biology, materials sciences, and medicine. A recent study of nine Ndm polyoxometalates (POM) showed their aqueous 5 mM solutions to be weakly luminescent, whereas no luminescence at all is seen for the aquo ion. In particular, the bis(POM) complexes better protect the Ndm ion from nonradiative deactivations, for instance t(4F3/2) = 411 6nsfor[Nd(PWn039)2]11- and67 2 ns for [Nd(As4W4oOi4o)]25 (But et al., 2005). 

Li, H., Qi, W, Li, W. et al. (2005) A highly transparent and luminescent hybrid based on the copolymerization of surfactant-encapsulated polyoxometalate and methyl methacrylate. Advanced Materials, 17, 2688-2692. 

In the last two decades, since about 1980, there has been an explosion of papers on these and other lanthanide/actinide polyoxometalates driven by several interests, e.g., radioactive-waste teatment, luminescence and emission, and other solid-state properties. 

Lu X, Liu X, Wang L, Zhang W, Wang C (2006) Fabrication of luminescent hybrid fibres based on the encapsulation of polyoxometalate into polymer matrices. Nanotechnology 17 3048-3053... 

Yan Z, Yan B (2014) Luminescent lanthanide-polyoxometalates assembling zirconia/alumina/ titania hybrid xerogels through task-specified ionic liquid linkage. RSC Adv 4 1735-1743... 

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