Quenching of the Excitonic Emission of ZnO Quantum Dots Due to Auger-Assisted Hole Transfer to CdS Quantum Dots

The charge-transfer mechanism in quantum dot (QD) donor acceptor systems is still poorly understood. Here, we utilize steady-state and time-resolved emission spectroscopy to study photoinduced hole transfer from ZnO to CdS QDs. The observed quenching of the excitonic emission (bothintensity and lifetime of ZnO QDs) in the presence of CdS QDs is attributed to the hole transfer from excited ZnO to CdS QDs. We have demonstrated that the variation of the hole-transfer rate with the driving force does not follow the conventional Marcus model but rather fits with a new Auger-assisted transfer mechanism, where the excess energy is used for electronic excitation. Moreover, we have evidenced the consequences of the hole transfer through the measurement of the enhanced photoconductivity of the film made of the blend of ZnO and CdS QDs.