Red electroluminescence from a thin organometallic layer of europium

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Abstract
We investigate the performance of organic electroluminescence devices employing a fluorinated diketone complex of europium (ETP) as the emitter material. The architecture of our devices isolates the emitter from the injecting contacts by sandwiching a thin layer of ETP between a hole-transporting diamine layer and an electron-transporting aluminum complex layer. The organic layers are deposited in high vacuum with rate-controlled sources onto glass substrates coated with indium–tin–oxide, and the cell is completed by evaporation of aluminum or calcium–aluminum cathodes. By varying the thickness of ETP layer in increments of 6 Å we demonstrate spatial confinement of the electroluminescence emission zone and optimal performance for an ETP thickness of 50 Å. Both the optical and electrical characteristics of these cells follow steep power-law relationships with voltage, which are indicative of trap-modified, space-charge-limited conduction. With aluminum cathodes we routinely achieve luminances up to 10 cd/m2 with direct current densities near 40 mA/cm2. The electroluminescence has a red–orange color and exhibits a narrow spectrum that is characteristic of trivalent europium ions.