Colloidal doping of thick nanoplatelets

Abstract

Semiconductor nanoplatelets (NPLs) make an interesting group of nanocrystals with unique optical properties as a result of their quasi 2-dimensional (2D) electronic structure. Such emerging fascinating optical features of NPLs include high absorption cross-section, narrow emission linewidths, and reduced Auger recombination, making them a superior choice compared to conventional semiconductor nanocrystals for optoelectronic applications. Doping of these materials with transition metals, such as silver and copper, provides great opportunities to modify and tune the electronic structure of these NPLs for various devices including light-emitting diodes and luminescent solar concentrators. Such doping with transition metals allows for manipulation of the photoluminescence from these NPLs, control of the recombination processes of the photogenerated carriers in these NPLs, and observation of the giant Zeeman effect as a result of exchange interactions between the dopants and carriers in these NPLs. Previously, CdSe NPLs have been doped with copper and silver only up to vertical thickness of 5 monolayers (ML). However, doping of thicker NPLs has not been possible to date. In this thesis work, we successfully doped thick CdSe NPLs having 7 ML in thickness with silver and copper using partial cation exchange to obtain large Stokes-shifted emission in the near-infrared (NIR) region. Here, the effect of precursor ratio and reaction temperature were systematically studied to tune the resulting emission. For both copper and silver dopants, we successfully quenched fully the band-edge emission, and purely dopantinduced emission was obtained. We also co-doped these NPLs with silver and copper, and we successfully obtained both copper- and silver-induced emissions from these NPLs. We further grew the CdZnS shell on 7 ML CdSe core by hot injection method and doped the resulting CdSe/CdZnS core/shell NPLs with silver and copper to push their emission further towards longer wavelengths in the NIR region. These thick doped-NPLs with large Stokes shift and emission in the NIR region present a promising platform for light-emitting and -harvesting applications.