Browsing by Subject "Partial cation exchange"
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Item Open Access Colloidal doping of thick nanoplatelets(Bilkent University, 2022-12) Ahmad, MuhammadSemiconductor 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.Item Open Access Colloidal synthesis of Ag(I)-doped CdSe nanoplatelets with partial cation exchange method(Bilkent University, 2019-01) Bozdoğan, İrfan SelimColloidal nanoplatelets (NPLs) exhibit strong one-dimensional quantum confinement in the vertical direction. This makes them a highly attractive host system for studying variable doping techniques and effects without variation in the quantum confinement effect. Earlier, core-only CdSe NPLs were converted into Cu2Se and HgSe NPLs, and also CdSe/CdS core/shell NPLs were transformed into Cu2Se/Cu2S, ZnSe/ZnS, and PbSe/PbS NPLs by using full cation exchange (CE) methods. Recently, core-only CdSe NPLs have been doped with Cu(I) ions using high-temperature nucleation doping and post-synthesis partial CE approaches. On the other hand, unlike Cu(I), such monovalent doping with Ag(I) ions has previously not been possible in NPLs as a host system, although silver doping had been widely studied in other host systems. Therefore, there has been no previous report on the doping of Ag(I) into CdSe NPLs to date. To address this gap, in this thesis, Ag(I) doping in CdSe NPLs by using a postsynthesis partial CE technique was developed. A systematic study was carried out to investigate the effects of dopant precursor reactivities, reaction timing, and temperature on the evolution of dopant-related emission as compared to the excitonic emission. In controlled experiments, the excitonic emission peak was eliminated and only dopant-related emission peak was successfully obtained. Finally, temperaturedependent emission kinetics of the as-synthesized Ag(I)-doped CdSe NPLs at varied temperatures ranging from 25 to 298 K were investigated. It was observed that both excitonic and dopant-related emission peaks were blue-shifted and their intensities were considerably increased with the decreasing temperature. As a new dopant-host system, these Ag(I)-doped CdSe NPLs hold a great promise for further systematic spectroscopic studies and possibly various optoelectronic applications.