Abstract

By comparing the phosphorescence spectra of Gd(acac)₃ (acac = acetylacetone), Gd(TFacac)₃ (TFacac = 1,1,1-trifluoroacetylacetone), the effects of fluorine replacement of hydrogen on the triplet state energy of the ligands were revealed. Fluorine can lower the triplet state energy of Hacac and make it more suitable for energy transfer towards the ⁵D₄ state of terbium. Organic electroluminescent devices (OELDs) with the corresponding trivalent terbium complexes as emissive layers were fabricated. Triple-layer-type devices with a structure of glass substrate/ITO (indium tin oxide)/PVK [poly(N-vinylcarbazole)]/PVK∶Tb complex: PBD [2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole]/PBD/Al exhibit bright green luminescence upon applying a dc voltage. The luminance of a device with Tb(TFacac)₃phen (1,10-phenanthroline) and Tb(TFacac)₃ as emissive layer is higher than that of the corresponding devices with Tb(acac)₃(phen) and Tb(acac)₃ as emissive layers. The EL device with Tb(TFacac)₃(phen) as emitter exhibits characteristic emission of Tb³⁺ ions with a maximum luminance of 58 cd m⁻² at 25 V.