Electrochemical and electroluminescent properties of some europium complexes and their terpolymers

The electrochemical and electroluminescent properties of some europium complexes and the terpolymers of 9-vinylcarbazole,methyl methacrylate and europium-methacrylate complex were investigated. Cyclic voltammetry measurements of poly(VK-co-MMA-co-Eu(BA)(2)(MAA) phen) (Cl) showed a quasi-reversible oxidation peak with onset of 0.75 V,and an irreversible reduction peak with onset of -1.8 V. The results demonstrated that this kind of multi-functional material has both hole- and electron-transporting properties. Some light-emitting diodes (LEDs) based on the europium containing complex and copolymers were fabricated. All these devices exhibited characteristic sharp red electroluminescence when forward biases were applied, and the turn-on voltage was in the range of 12 similar to 27 V. A maximum brightness of 52 cd/m(2) with a luminous efficiency of about 0.031 1m/W was achieved from a single-layer device based on the multi-functional copolymer C3. EL spectra of the devices showed that the emissions were from the corresponding lanthanide-complex units,instead of carbazole groups of the copolymers. It is suggested that the carbazole groups in Cn serve as hole-transport material while electron transfer may occur through the lanthanide-containing moieties of the same copolymer.