Design of efficient electroluminescent lanthanide(III) complexes

The lanthanide complexes have been anticipated to exhibit high efficiency a long with a narrow emission spectrum. Photoluminescence for the lanthanide complex is characterized by a high efficiency since both singlet and triple t excitons are involved in the luminescence process. However, the maximum e xternal electroluminescence quantum efficiencies have exhibited values arou nd 1% due to triplet-triplet annihilation at high current. Here, we propose d a new energy transfer mechanism to overcome triplet-triplet annihilation by the Eu. complex doped into phosphorescent materials with triplet levels that were higher than singlet levels of the Eu complex. In order to show th e feasibility of the proposed energy transfer mechanism and to obtain the o ptimal ligands and host material, we have calculated the effect depending o n ligands as a factor that controls emission intensity in lanthanide comple xes. The calculation shows that triplet state as well as singlet state of a nion ligand affects on absorption efficiency indirectly.