In this work, interference and coherence phenomena, appearing in atomic and molecular ensembles interacting with coherent light sources, as electromagnetically induced transparency (EIT), coherent population trapping (CPT), and slow group velocity of light are investigated. The goal of the project is to make the steps towards various applications of these phenomena, first, by studying them in solid media (which are the most advantageous for applications), second, by suggesting some novel applications such as CPT-based plasma diagnostics, and realization of new types of solid-state lasers (based on suppression of excited-state absorption via EIT). The third goal of the project is extension of coherence and interference effects well-known in optics to the gamma-ray range of frequencies and, correspondingly, from atomic to nuclear transitions. A particular technique of chirped pulse compression applied to M??ossbauer transitions is considered and the possibility of compression of M??ossbauer radiation into ultrashort gamma-ray pulses is analyzed. The theoretical treatment of the interference and coherence effects is based on the semiclassical description of atom-light interaction, which is sufficient for correct analysis of the phenomena considered here. Coherent media are considered in two-, three-, and four-level approximations while their interaction with light is studied both analytically and numerically using the Maxwell-Bloch set of equations.

The vibrational potential energy surfaces in electronic ground and excited states of several ring molecules were investigated using several different spectroscopic methods, including far-infrared (IR), Raman, ultraviolet (UV) absorption, fluorescence excitation (FES), and single vibronic level fluorescence (SVLF) spectroscopies. Based on new information obtained from SVLF and millimeter wave spectra, the far-IR spectra of coumaran were reassigned and the one-dimensional ring-puckering potential energy functions for several vibrational states in the S0 ground state were determined. The barrier was found to be 154 cm-1 and the puckering angles to be ± 25°, in good agreement with the millimeter wave barrier of 152 cm-1 and puckering angles of ± 23°. Moreover, the UV absorption and FES spectra of coumaran allowed the one-dimensional ring-puckering potential energy functions in the S1 excited state to be determined. The puckering barrier is 34 cm-1 for the excited state and the puckering angles are ± 14°. Several calculations with different basis sets have been carried out to better understand the unusual vibrational frequencies of cyclopropenone. It was shown that there is strong interaction between the C=O and symmetric C-C stretching vibrations. These results differ quantitatively from a previous normal coordinate calculation and interpretation. The vapor-phase Raman spectrum of 3,7-dioxabicyclo[3.3.0]oct-1,5-ene was analyzed and compared to the predicted spectrum from DFT calculations. The spectrum further shows it has D2h symmetry, in which the skeletons of both rings are planar. The infrared and Raman spectra of vapor-phase and liquid-phase 1,4-benzodioxan and 1,2,3,4-tetrahydronaphthalene were collected and the complete vibrational assignments for both molecules were made. Theoretical calculations predicted the barriers to planarity to be 4809 cm-1 for 1,2,3,4-tetrahydonaphthalene and 4095 cm-1 for 1,4-benzodioxan. The UV absorption, FES, and SVLF spectra of both molecules were recorded and assigned. Both one and two-dimensional potential energy functions of 1,4-benzodioxan for the ring-twisting and ring-bending vibrations were carried out for the S0 and S1(π,π*) states, and these were consistent with the high barriers calculated for both states. The low-frequency spectra of 1,2,3,4-tetrahydronaphthalene in both S0 and S1(π,π*) states were also analyzed.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

No description available.

Thesis (Ph.D.)--Bowling Green State University, 2009. / Document formatted into pages; contains xvii, 186 p. : ill. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 274-296). Available also in a digital version from Dissertation Abstracts.

In this thesis we describe the development of a real-space implementation of the Bethe-Salpeter equation (BSE) and use it in conjunction with a semi-empirical tight-binding model to investigate the optoelectronic properties of colloidal quantum- confined nanostructures. This novel implementation exploits the limited radial extent and small size of the atomic orbital basis to treat finite systems containing up to ∼4000 atoms in a fully many-body framework. In the first part of this thesis our tight-binding model is initially benchmarked on zincblende CdSe nanocrystals, before subsequently being used to investigate the electronic states of zincblende CdSe nanoplatelets as a function of thickness. The band-edge electronic states are found to show minimal variation for a range of thicknesses and the results of our tight-binding model show good agreement with those predicted using a 14-band k·p model for a nanoplatelet of 4 monolayers (ML) in thickness. Optical absorption spectra were also computed in the independent-particle approximation. While the results of the tight-binding model show good agreement with those of the 14-band k·p model in the low-energy region of the spectrum, agreement with experiment was poor. This reflects the need for a many-body treatment of optical absorption in nanoplatelet systems. In the second part of this thesis we apply our tight-binding plus BSE model to study the excitonic properties of CdSe nanocrystals and nanoplatelets. Simulations performed on CdSe nanocrystals examined an approximation of the BSE equivalent to configuration interaction singles (CIS), and found that both the optical gap and the low-energy spectral features were unaffected by the approximation. A comparison of exciton binding energies with those predicted by CIS demonstrates the sensitivity of results to the exact treatment of dielectric screening and the decision of whether or not to screen exchange. Our model predicts optical gaps that are in strong agreement with average experimental data for all but the smallest diameters, but was not able to reproduce low-energy spectral features that were fully consistent with experiment. This was attributed to the absence of the spin-orbit interaction in the model. Simulations performed on CdSe nanoplatelets investigate the optical gaps and exciton binding energies as a function of thickness. Exciton binding energies were found to reach ∼200 meV for the thinnest system, however, optical gaps were slightly overestimated in comparison to experiment. This is attributed to the reduced lateral dimensions used in our simulations and our bulk treatment of dielectric screening. A two-dimensional treatment of dielectric screening is expected to further increase binding energies. Calculations of the excitonic absorption spectrum reproduce the characteristic spectral features observed in experiment, and show strong agreement with the spectra of nanoplatelets, with thicknesses ranging from 3 ML to 5 ML.

Doctor of Philosophy / Department of Chemistry / Christine Aikens / Thiolate-protected noble metal nanoparticles (~2 nm size) are efficient solar photon harvesters, as they favorably absorb within the visible region. Clear mechanistic insights regarding the photo-physics of the excited state dynamics in thiolate-protected noble metal nanoclusters are important for future photocatalytic, light harvesting and photoluminescence applications. Herein, the core and higher excited states lying in the visible range are investigated using the time-dependent density functional theory method for different thiolate-protected nanoclusters. Nonadiabatic molecular dynamics simulations are performed using the fewest switches surface hopping approach with a time-dependent Kohn-Sham (FSSH-TDKS) description of the electronic states with decoherence corrections to study the electronic relaxation dynamics. Calculations on the [Au₂₅ (SH)₁₈]⁻¹ nanocluster showed that relaxations between core excited states occur on a short time scale (2-18 ps). No semiring or other states were observed at an energy lower than the core-based S₁ state, which suggested that the experimentally observed picosecond time constants could be core-to-core transitions rather than core-to-semiring transitions. Electronic relaxation dynamics on [Au₂₅ (SH)₁₈]⁻¹ with different R ligands (R = CH₃, C₂H₅, C₃H₇, MPA) [MPA = mercaptopropanoic acid] showed that all ligand clusters including the simplest SH model follow a similar trend in decay within the core states. In the presence of higher excited states, R= H, CH₃, C₂H₅, C₃H₇ demonstrated similar relaxations trends, whereas R=MPA showed a different relaxation of core states due to a smaller LUMO+1-LUMO+2 gap. Overall, the S₁ state gave the slowest decay in all ligated clusters. An examination of separate electron and hole relaxations in the [Au₂₅ (SCH₃)₁₈]⁻¹ nanocluster showed how the independent electron and hole relaxations contribute to its overall relaxation dynamics. Relaxation dynamics in the Au₁₈(SH)₁₄ nanocluster revealed that the S₁ state has the slowest decay, which is a semiring to core charge transfer state. Hole relaxations are faster than electron relaxations in the Au₁₈(SH)₁₄ cluster due its closely packed HOMOs. The dynamics in the Au₃₈(SH)₂₄ nanocluster predicted that the slowest decay, the decay of S₁₁ or the combined S₁₁-S₁₂, S₁-S₂-S₄-S₇ and S₄-S₅-S₉-S₁₀ decay, involves intracore relaxations. The phonon spectral densities and vibrational frequencies suggested that the low frequency (25 cm⁻¹) coherent phonon emission reported experimentally could be the bending of the bi-icosahedral Au₂₃ core or the “fan blade twisting” mode of two icosahedral units. Relaxation dynamics of the silver nanoparticle [Ag₂₅ (SR)₁₈]⁻¹ showed that both [Ag₂₅(SH)₁₈]⁻¹ and [Au₂₅ (SH)₁₈]⁻¹ follow a common decay trend within the core states and the higher excited states.

Magister Scientiae - MSc (Chemistry) / Nanoscience and nanotechnology are known to be interdisciplinary, crossing and combining various fields and disciplines in pursuit of desirable outcomes. This has brought about applications of nanoscience and nanotechnology in multitudes of industries, spanning from the health, pharmaceutical to industrial industry. Within the health industry, the medical field has seen much advancement through nanoscience and nanotechnology. The importance of finding cures to diseases is top priorities within the medical field, along with advancements in understanding and diagnosing diseases. Due to these outcomes, we see the emergence of imaging techniques playing a crucial role. The work covered in this thesis looks at a prospective luminescent agent applicable in the medical field for bio-imaging, but also at a possible phthalocyanine sensitizer for treatment of cancer through photodynamic therapy. Another area where nanoscience and nanotechnology are found is in industry, where nanoparticles are utilised as catalysts in many synthetic reactions. Highly desirable catalysts in industry are those involved in oxidative reactions where we explore a metal nanoparticle catalyst within this work.