Ultrafast Photoluminescence Quenching of Initially Excited States in CdSe Quantum Dots Functionalized with a Charge Acceptor Dye

2019 
CdSe quantum dots have interesting carrier transfer characteristics and can be used as photon collectors in certain kinds of hybrid photovoltaic devices. Some of these systems work through a charge transfer process from an excitonic state to a surface-adsorbed organic dye. In this article, we explore carrier transfer time scales through the characterization of the ultrafast photoluminescence behavior of nanocrystal excitonic states in the presence of adsorbed molecular charge acceptors. We show that upon physisorption of the cyanine dye Indocyanine Green, significant emission quenching due to carrier transfer can take place in a direct way from the initially pumped states in 5.7 nm diameter CdSe dots. We show that such transfer takes place independently of the excess energy above the band gap. Importantly, this near-instantaneous quenching is responsible for the loss of an important fraction of the excitonic population on a time scale much faster than intraband (hole and electron) excitonic relaxation. Th...
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