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 photoluminesce nce (PL) spectrum of the samples consists of three bands: an exciton b and 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 v olume of the particles, while the G band relates to surface defects. T he 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 addit ional fast intrinsic decay component in the sub-nanosecond time scale that may be superradiative in nature. The analysis of the decay dynami cs in the nanosecond regime requires a distributed kinetic model, base d on the Kohlraushch-Williams-Watts (KWW) stretched exponential functi on. The experimental results are consistent with detrapping and repopu lation professes, in which excited carriers can relax to lower lying s urface states (associated with the G band). Thermal detrapping from th ese states and repopulation of the exciton and L band states results i n a long multiexponential decay. The microsecond decay of L and G band s obeys a donor-acceptor recombination characteristic dynamics.