Dynamics of recombination processes in PbI2 nanocrystals embedded in porous silica films

The present paper discusses the dynamics of recombination processes in PbI2 nanocrystals embedded in porous silica films. The photoluminescence (PL) spectrum of the samples consists of three bands: an exciton band near 2.5 eV and two deeper bands centered at 2.44 eV (L band) and 2.03 eV (G band). The L band relates to bulk defects in the internal volume of the particles, while the G band relates to surface defects. The dynamics of the different recombination events was investigated by continuous and time-resolved PL techniques. All three peaks exhibit a complex decay, which consists of several multiexponential components, progressing from nanoseconds to microseconds. The exciton has an additional fast intrinsic decay component in the sub-nanosecond time scale that may be superradiative in nature. The analysis of the decay dynamics in the nanosecond regime requires a distributed kinetic model, based on the Kohlraushch-Williams-Watts (KWW) stretched exponential function. The experimental results are consistent with detrapping and repopulation professes, in which excited carriers can relax to lower lying surface states (associated with the G band). Thermal detrapping from these states and repopulation of the exciton and L band states results in a long multiexponential decay. The microsecond decay of L and G bands obeys a donor-acceptor recombination characteristic dynamics.