1.1 μ m near-infrared electrophosphorescence from organic light-emitting diodes based on copper phthalocyanine

We demonstrated near-infrared organic light-emitting devices employing copper phthalocyanine (CuPc) doped into 4,4′-N,N′-dicarbazole-biphenyl (CBP). Room-temperature electrophos-phorescence was observed at about 1.1μm due to transitions from the first excited triplet state to the singlet ground state (T1-S0) of CuPc. There existed very weak emission of CBP from undoped devices, and at lower doping concentrations (⩽12wt%) the driving voltages of doped devices were higher than that of undoped devices. The results indicated that Förster [Ann. Physik. (Leipzig) 2, 55 (1948)] and Dexter [J. Chem. Phys. 21, 836 (1953)] energy transfers play a minor role in these devices, and direct charge trapping appears to be the dominant mechanism.