The invention provides a novel quadridentate bridging ligand, an iridium complex thereof, and a bimetallic complex of iridium and rare-earth ions. The quadridentate bridging ligand is a bipyridine derivative containing beta-diketone, the bimetallic complex has a structure of formula (III), wherein, RE is rare-earth element; L1, L2 are cyclic metal ligands combined with Ir; D1, D2 and D3 are anion ligands; X, Y are C or nitrogen atom; m, n is the number of the atom, m+n=0, 1 or 2; R1, R2, R3 are hydrogen atom, halogen atom, nitryl, amido, alkyl, alkenal, alkynyl, alkoxy, aryl or heterocyclic aryl, R4 is alkyl, halogen-substituted alkyl, aryl or heterocyclic aryl. The iridium-rare-earth bimetallic complex is luminescent through the iridium complex sensitizing rare-earth ions, has an important characteristic excited by visible light, thereby the iridium-rare-earth bimetallic complex has wide application as new luminescence material.