Patent ID: 8173271

Claim:
A rare earth complex comprising: a lanthanide ion (Ln), a phosphine oxide ligand, and a β-diketone ligand or a sulfonyl amide ligand, wherein the rare earth complex is represented by one of complex (2) or complex (4) wherein R a1 , R a2 , R a4 and R a5 , R b1 and R b2 and R c1 and R c2 are the same or different substituents selected from a group consisting of hydroxyl, a halogen atom, an alkyl group containing 1 to 20 carbon atoms, a perfluoroalkyl group containing 1 to 20 carbon atoms, an alkoxy group containing 1 to 20 carbon atoms, phenyl, biphenyl, naphthyl, a heterocyclic group, and a substituted group thereof and n is an integer of 1 to 7, wherein said phosphine oxide ligand contains a phosphorus atom connecting to at least one phenyl group the para-position of which is not substituted but at least one of the meta-positions of which is substituted with a substituent selected from the group consisting of an alkyl group containing 1 to 20 carbon atoms, a perfluoroalkyl group containing 1 to 20 carbon atoms, an alkoxy group containing 1 to 20 carbon atoms, phenyl, biphenyl, naphthyl, a heterocyclic group, and a substituted group thereof; hydroxyl and a halogen atom.