Master of Science
Indika U. Arachchige
Research in nanoscience has gained noteworthy interest over the past three decades. As novel chemical and physical properties that are vastly different from extended solids are realized in nanosized materials, nanotechnology has become the center of attention for material in research community. Much to our amazement, investigations in the past two decades revealed that the nanocrystalline semiconductors are “THE PRIME CANDIDATES” to meet the growing energy demand, sensor development, cellular imaging and a number of other optoelectronic applications. Nonetheless, synthesis of nanostructures with control over physical parameters is not sufficient, yet assembling them into functional nanoarchitectures with unique and tunable physical properties is critical for device integration studies. Among bottom-up assembling methods, sol-gel method has received noteworthy interest to produce macroscopic nanostructures of metal and semiconductor NPs with no use of intervening ligands or supports.
In 2005, condensation of pre-formed semiconductor NPs (CdSe, CdS, ZnS and PbS) into voluminous gels is reported via controlled destabilization of the surfactant ligands. The resultant chalcogenide aerogels are reported to exhibit extremely low density, high surface area and porosity, and quantum confined optical properties of the NP building blocks. More recently, this method has been extended for the assembly of metal NPs, where transparent and opaque nanostructures (aerogels) of Ag and Au/Ag NPs were produced. The aerogels produced by condensation of NPs are low dimensional (fractal) nanostructures and exhibit a physically connected network of colloidal NPs. Interactions between NPs in a gel structure are intermediate of those of the ligand stabilized NPs and core/shell hetero-nanostructures (e.g. Au@CdSe NPs) with the potential to couple chemically dissimilar systems. In this research study, NP condensation strategy has been utilized to efficiently integrate the plasmonic and excitonic properties of metal and semiconductor nanostructures to produce high-efficiency hybrids that exhibit unique tunable physical and photophysical properties.
Two hybrid systems composed of spherical CdSe/Ag hollow NPs and rod shaped CdSe/Ag hollow NPs were investigated for the fabrication of metal-semiconductor hybrid aerogels. The first excitonic energy of spherical CdSe NPs is overlapped with the plasmonic energy of Ag hollow NPs at 515 - 530 nm. The second excitonic energy of rod shaped CdSe is overlapped with the plasmonic energy of Ag hollow NPs at 490 - 505 nm. The photophysical properties of both systems were thoroughly probed through UV-Visible absorption, photoluminescence (PL), and time-resolved (TR) PL spectroscopy. A novel hybrid emission emerged at 640 nm (for spherical CdSe/Ag hollow NPs) and 720 nm (for rod shaped CdSe/Ag hollow NPs) with ~0.2-1% Ag loading. TRPL studies revealed 685 ns and 689 ns PL decay times for hybrid emissions, which are vastly different from the band-edge and trap state emission of phase pure spherical and rod shaped CdSe aerogels respectively, supporting the generation of novel radiative decay pathways. Overall, synthesis of CdSe/Ag hybrid aerogels with novel/tunable photophysical properties will add to the toolbox of semiconductor aerogels with the potential application in future light harvesting technologies.
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Available for download on Tuesday, May 03, 2022