Direct observation of host–guest triplet–triplet annihilation in phosphorescent solid mixed films



Triplet–triplet annihilation (TTA) between excited states of host and guest species in organic mixed films, comprising a phosphorescent heavy-metal complex, is usually only accessed indirectly, as one is only able to monitor the radiative guest phosphorescence. We compare two different host materials, 4,4′,4″-tris(N -carbazolyl)-triphenylamine (TCTA) and 4,4′-N,N ′-dicarbazole-biphenyl (CBP) in combination with the green emitter fac -tris(2-phenylpyridine) iridium which differ in their triplet state energy. At excitation levels in the saturation range of guest emission, we observe increasing non-linearities in photoluminescence transients with increasing excitation power for the CBP host material, which can directly be attributed to TTA of host and guest excited states. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)