Size-Dependent Carrier Dynamics in CdS Nanoparticles by Femtosecond Visible-Pump/IR-Probe Measurements

Abstract

Ultrafast photoexcited carrier dynamics in CdS nanoparticles prepared by an AOT/n-heptane reversed micelle system were investigated by a femtosecond visible-pump/mid-IR probe technique. A mid-IR probe beam was found to mainly probe the ultrafast dynamics of photoexcited electrons in the conduction band. Dispersions of CdS nanoparticles with 8 different mean diameters from 2.9 to 4.1 nm were prepared by tuning the mole ratio between water and AOT (W ) [H 2 O]/[AOT]) in the reversed micelle systems. The excited state lifetime strongly depended on the mean size of CdS nanoparticles with a maximum around a mean diameter of 3.5 nm. This result was explained by considering the balance between the carrier recombination rates via surface states and those via interior states. The relationship between the excited state lifetime and the size of CdS nanoparticles was drastically changed when the surface was terminated by thiol molecules.

Nanoscale Strategies for Light Harvesting

“…122 Actually, the electron−hole exchange interaction influences the decay kinetics of QDs, which eventually depends on the size of the QDs. 123,124 Further, Yagi et al 125 have described the size-dependent relxation dynamics of CdS QDs and it is found that the fast decay component is increased upon decreasing the size of QDs because of the surface states are decreased in larger QDs. It is also evident that the relaxation decay of photoexcited QDs is influenced by the densities of surface and interior trap states of QDs.…”

Carrier relaxation dynamics in InAs/InGaAlAs quantum dashes

“…We attribute the fast relaxation component to free carriers and the slow component to trapped carriers, which is a common situation in semiconductor nanostructures and was previously observed in quantum dot systems [10,11]. Size dependence of the fast decay component can be understood by considering surface states that act as recombination centers.…”

Relationship between the Photocatalytic Hydrogen Ion Reduction and Charge Carrier Dynamics of Pt/Cd1–xNixS Catalysts

“…TA spectra of CdS, Pt/CdS, Cd 0.99 Ni 0.01 S, and Pt/Cd 0.99 Ni 0.01 S were recorded upon 390 nm excitation (energy ≈ 40 μJ/pulse). The fs-TA spectra of CdS and Pt/CdS have been studied by others previously. − In brief, a negative signal centered at ca. 480 nm, ground state bleaching (GSB), was seen and assigned to state filling electron levels with negligible contribution from holes. − A broad positive signal at and above 600 nm, photon induced absorption (PIA), however, was ambiguously assigned to both electrons and holes , in the literature.…”