Phosphorescence Decay Process of Ir(ppy)3 : Temperature Dependence of Decay Time

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Abstract
Theoretical calculation has been undertaken on the photoluminescence (PL) lifetime of fac tris(2-phenylpyridine) iridium (Ir(ppy)3) doped in polymethyl methacrylate (PMMA) and 4,4'-N,N'-dicarbazole-biphenyl (CBP), and its temperature dependence at 0–300 K. The emitting triplet state consists of three zero-field splitting substates. Taking into account one-phonon non-radiative transitions among these substates, the rate equations for the populations of these substates are solved numerically and three PL lifetimes are derived. The long PL lifetime increases considerably with decreasing temperature from 300 to 0 K, while the two short lifetimes increase very little. A good agreement has been obtained for the temperature dependence between the calculated long lifetime and the observed one for Ir(ppy)3 in PMMA and CBP. Temperature dependence of PL intensity has been also calculated under the three-substate model. The result is consistent with the observed temperature-independence of intensity.