Dynamics of Recombination Processes in PbI2 Nanocrystals Embedded in Porous Silica Films

The present paper discusses the dynamics of recombination processes in PbI 2 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 processes, 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.