Carrier Dynamics In Nanocrystals Research Articles

Tuning Electron-Phonon Interactions in Nanocrystals through Surface Termination.

We perform ab initio molecular dynamics on experimentally relevant-sized lead sulfide (PbS) nanocrystals (NCs) constructed with thiol or Cl, Br, and I anion surfaces to determine their vibrational and dynamic electronic structure. We show that electron-phonon interactions can explain the large thermal broadening and fast carrier cooling rates experimentally observed in Pb-chalcogenide NCs. Furthermore, our simulations reveal that electron-phonon interactions are suppressed in halide-terminated NCs due to reduction of both the thermal displacement of surface atoms and the spatial overlap of the charge carriers with these large atomic vibrations. This work shows how surface engineering, guided by simulations, can be used to systematically control carrier dynamics.

Radiative and nonradiative recombination of self-trapped exciton on silicon nanocrystal interface

The theory of the multiphonon and radiative recombination of a selftrapped exciton on the interface of a sil� icon nanocrystal in a SiO2 matrix is developed. Selftrapped excitons play a key role in the hot carrier dynam� ics in nanocrystals under photoexcitation. The ratio of the probabilities of the multiphonon and radiative recombination of the selftrapped exciton is estimated. The probabilities of exciton tunnel transition from the selftrapped state to a nanocrystal are calculated for na nocrystals of various sizes. The infrared range spec� trum of the luminescence of the selftrapped exciton is obtained.

Ultrafast Interfacial Charge Carrier Dynamics in ZnSe and ZnSe/ZnS Core/Shell Nanoparticles: Influence of Shell Formation

The post-preparative irradiation of water-soluble thiol-stabilized ZnSe colloidal nanocrystals (NCs) leads to a strong increase of the photoluminescence quantum yield of UV blue emission. The altered photoluminescence properties of the colloidal samples have been explained previously by changes in particle composition, size, and surface modification accompanying irradiation. In this work, the charge carrier dynamics in NCs before and after irradiation treatment has been examined via femtosecond transient absorbance spectroscopy in the UV−visible spectral region. Upon adsorption of the electron acceptor methylviologen (MV2+), an ultrafast heterogeneous electron transfer from the conduction band of the nanocrystals to MV2+ is observed and studied. Therefore, the employment of the MV2+ helps to assign the observed dynamics to electron or hole relaxation processes. It is shown that a ZnSe/ZnS core/shell structure is formed during the post-preparative treatment. The transient absorbance measurements of the MV2...

Modification of carrier dynamics in CdSe nanocrystals by excess Cd in deposition bath

Photoexcited carrier dynamics in thin CdSe nanocrystalline films prepared by chemical bath deposition are strongly dependent on the deposition parameters. In this paper, we show how an increase in concentration of CdSO 4 in deposition bath affects the photoexcited carrier dynamics in nanocrystals. We used ultrafast absorption and photoluminescence laser spectroscopy to compare the carrier dynamics in samples prepared with and without increased CdSO 4 concentration. We have found that in the Cd-rich samples the spectral dependences of both photoluminescence and absorption dynamics are considerably less pronounced and the dynamics are slower. The observed effects were explained by the suppression of surface mediated carrier relaxation due to the passivation of individual nanocrystals by cadmium hydroxide and/or by sulphatocomplexes of Cd 2+.