INTRAMOLECULAR ENERGY-TRANSFER IN POLYOXOMETALOEUROPATE LATTICES AND THEIR APPLICATION TO AC ELECTROLUMINESCENCE DEVICE

Crystal Structures of four polyoxometaloeuropates, Na9[EuW10O36].32H2O (1), K15H3[Eu3(H2O)3(SbW9O33)(W5O18)3].25.5H2O (2), [NH4]12H2[Eu4(H2O)16(MoO4)(Mo7O24)4].13H2O (3), and Eu2(H2O)12[Mo8O27].6H2O (4) are investigated to understand the relaxation process of the oxygen-to-metal (O-->M) charge-transfer excitation energy in the polyoxometalate lattice. The temperature dependence of the intramolecular energy transfer from the O-->M LMCT states to Eu3+ in the polyoxometaloeuropate lattices indicates that the M-O-M and Eu-O-M bond angles of about 150-degrees allow the hopping of d1 electron among MO6 octahedra and to EuO8 (or EuO9) site to be the deactivation of the O-->M LMCT state due to the deactivated recombination between the electron and hole in the lattice. Co-ordination of aqua ligands to Eu3+ leads to a decrease in lifetime of the emitting state of 5D0, due to the vibronic coupling of the 5D0 state with the vibrational states of high frequency OH oscillators. Dispersion-typed electroluminescence (EL) cell is constructed with a highly photoluminescent [EuW10O36]9- system. With a.c. excitation to the divice consisting of the doublet structure of emissive [EuW10O36]9- and insulating Mylar film layers, the [EuW10O36]9- layer exhibits EL which matches the photoluminescence spectrum of the solid. A multicolor display in combination with other polyoxometalolanthanoates is possible.