Using density functional theory (DFT) and time dependent DDFT (TDDFT), we simulate the oxidation process on the surface of Pb16Se16 and Pb68Se68 QDs and its effect on their electronic and optical properties. When oxygen is substituted for Se ions, the electronic properties of the QD are insignificantly perturbed. In contrast, if oxygen is adsorbed on the QD surface and coordinated with two Pb ions, it introduces additional unoccupied states inside the QD's band gap, so called mid-gap states. Such states are hybridized between the oxygen and the QD's surface atoms and contribute to the lowest-energy optically dark or semi-dark transitions likely resulting in quenching of the QD luminescence. In contrast, if the oxygen is coordinated with Se and Pb ions on the surface, the mid-gap states are not present and the optical transitions are similar to those of the non-oxidized QDs. Similar behavior was also found for halide radicals. However, the trap states are eliminated for halides in their ionic form or in a form of lead salts (PbCl2 or PbI2). The presence of other surface ligands such as primary amines insignificantly affects the electronic structure of QDs, but increases the binding energy of neighboring halide ions, favoring their attachment to the (111) and (110) surfaces of the PbSe QDs.

Adsorption of halides and oxygen on the PbSe quantum dots: DFT calculations

248th National Meeting (2014)

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