Lifetime fluctuations of a single emitter in a disordered nanoscopic system:: The influence of the transition dipole orientation

We study the fluctuations of the fluorescence decay rate of a single emitter in a random cluster of nanoparticles, in a regime dominated by near-field scattering. Configurational changes of the environment induce statistical changes of the decay rate. Two regimes are considered which differ in terms of transition dipole orientation. In one regime, the orientation of the transition dipole is assumed to remain constant while the configuration of the cluster changes randomly. In another regime, the orientation of the transition dipole is assumed unknown and continuously averaged over the three directions of space. Using exact numerical simulations and a simple analytical model, we show that the statistical distributions of the spontaneous decay rate are substantially different in both regimes. In both cases, the decay rate fluctuations are strongly dependent on the level of absorption at the nanoscale. We discuss the impact of this result in terms of imaging in complex media. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.