A theoretical interpretation of the abnormal 5D0→7F4 intensity based on the Eu3+ local coordination in the Na9[EuW10O36] • 14H2O polyoxometalate

The Na-9[EuW10O36]center dot 14H(2)O polyoxometalate studied here has shown a peculiar 4f-4f emission spectrum that has two main differences in comparison to data reported previously in the literature: a D-5(0)-> F-7(0) line with much smaller intensity and an abnormally high intensity of the D-5(0)-> F-7(4) transition. These results have been theoretically interpreted in terms of the Omega(lambda) intensity parameters and their dependence on the nature and local symmetry of the chemical environment around the Eu3+ ion, leading to the conclusion that the chemical environment is highly polarizable with a local symmetry corresponding to a slightly distorted D-4d coordination geometry. Further evidences corroborating this interpretation were obtained by progressively dissolving the polyoxometalate in water, inducing a progressive accommodation of the coordination polyhedron towards lower symmetries. (c) 2006 Elsevier B.V. All rights reserved.