Molecular electrophosphorescence in (Sm, Gd)-β-diketonate complex blend for OLED applications

In this work the preparation and characterization of the triple-layer organic light-emitting diode (OLED) using a mixture of the samarium and gadolinium β-diketonate complexes [Sm0.5Gd0.5(TTA)3(TPPO)2] as emitting layer is reported. The OLEDʹs devices contain 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1ʹ-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline aluminum) (Alq3) as electron transporting layer. The electroluminescence spectrum present emission narrow bands from the 4G5/2→6HJ transitions (where J=5/2, 7/2 and 9/2) characteristic of the Sm3+ ion. These sharp lines are overlapped with a broad band attributed to the electrophosphorescence from the T1→S0 transition in the ligand TTA. The intramolecular energy transfer is discussed and applied on the change of the emission color of the organic LEDs at different bias voltages.