Two novel second ligands, 9,9-Di-(4-methoxyphenyl)-9-H-4,5-Diazafluorene (OMe-Spiro-DF) and 9,9-Di-(2-(4-(4-butyloxy)phenyl)-5phenyl-1,3,4-oxadiazolyl)-phenyl-9-H-4 ,5 Diazafluorene (OXD-Spiro-DF), were successfully prepared. Europium complexes, Eu(DBM)(3)(OMe-Spiro-DF) and Eu(DBM)(3)(OXD-Spiro-DF) (DBM=dibenzolylmethane) based on the two ligands were designed and synthesized. For a double-layer device with configuration of indium tin oxide (ITO)/N,N' -diphenyl-N,N' -bis(3-methylphenyl)-1,1' biphenyl-4,4'-diamine (TPD)/Eu(DBM)(3)(OXD-Spiro-DF) or Eu(DBM)3(OMe-Spiro-DF)/Mg/Ag, compared with the device based on complex Eu(DBM)(3)(OMe-Spiro-DF), the brightness and electroluminescent (EL) efficiency of device based on complex Eu(DBM)(3)(OXD-Spiro-DF) with oxadiazole-functionalized ligand OXD-Spiro-DF are significantly improved due to the improvement of electron-transporting ability. A maximum brightness of 154 cd/m(2) was obtained at 17 V in the complex Eu(DBM)3(OXD-Spiro-DF), about four times brighter than the corresponding complex Eu(DBM)(3)(OMe-Spiro-DF). (c) 2004 Elsevier B.V. All rights reserved.