Doctor of Philosophy (PhD)
In the first part of this dissertation, the adsorption isotherms, resonance coupling, and fluorescence of molecular dyes on the surface of plasmonic nanoparticles are investigates. SHG is also used to investigate the growth of a silver shell on the surface of gold nanoparticles in real time. Additionally, gold-silver-gold core-shell-shell nanoparticles possess extinction peak wavelengths that can be controlled over the visible and near-infrared regions and enhanced photothermal effect. Transient absorption measurements determine that the phonon-phonon scattering lifetime is considerably faster in the core-shell-shell nanoparticles than in the gold nanospheres and gold nanorods, which contributes to the higher photothermal efficiencies. Transient absorption is also used to investigate the ultrafast excited-state relaxation dynamics of the different dyes adsorbed on the core-shell-shell surface and the size-dependent dynamics o interfacial charge transfer between the gold nanoclusters and the TiO2 bandgap in TiO2-Au nanocomposites. In the second part of this dissertation, the ultrafast spectroscopy of size-selected ([Ru(bipy)3][BETI]2) nanoGUMBPS are reported. The nanoGUMBOS show spectral shifts and size-dependent relaxation dynamics. Long-lived acoustic phonon oscillations with size-dependent frequencies are also observed, where the phonon frequency increases as the nanoparticle size increases, suggesting a very low coupling between electronic and phonon degrees of freedom and a strong hydrophobic interaction with the aqueous solvent. Furthermore, Transient absorption measurements of porphyrin-based nanoGUMBOS reveal that efficient electron transfer and energy transfer is observed between the porphyrin groups leading to shorter excited-state lifetimes. Additionally, the excited-state dynamics of brilliant green – BETI and carbazole – BETI nanoGUMBOS are investigated using pump-probe transient absorption. Brilliant green – BETI nanoGUMBOS exhibit enhanced NIR fluorescence compared to the parent dye in water. The overall excited-state dynamics of brilliant green molecular dye in water are longer than those in the colloidal nanoGUMBOS. The torsional degrees of freedom of the phenyl ring in brilliant green are hindered in the nanoGUMBOS. Additionally, the SHG signal of [BG][BETI] nanoGUMBOS is remarkably enhanced due to the increase of the second order susceptibility tensor χ^((2)) of the nanoGUMBOS. Transient absorption measurement of carbazole – BETI nanoGUMBOS reveal the presence of optical gain and stimulated emission during the excited-state relaxation dynamics.
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Karam, Tony Eugene, "Ultrafast and Nonlinear Spectroscopy of Colloidal Nanomaterials" (2016). LSU Doctoral Dissertations. 515.
Haber, Louis H