Thesis (M. Phil.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 93-101).

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 215-216). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 17, 2009) Includes bibliographical references (p. 67-70).

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Devido à necessidade da construção de dispositivos integrados (por exemplo micro laser e inversor óptico), estudos espectroscópicos em amostras altamente dopadas são necessários. Entretanto, o procedimento de se utilizar amostras com alta concentração traz consigo o problema da supressão da luminescência, devido a processos de transferência de energia mais intensos. Portanto, neste trabalho, estudamos os processos de transferência de energia que diminuem a luminescência na região do infravermelho utilizando amostras vítreas à base de fluoreto (fluoroindato e fluorozircoaluminato), dopados com Er+3 em concentrações que variam de 0.1 a 20 mol%Er. Obtivemos parâmetros de transferência de energia através de um modelo para os níveis do Er+3 (sistema de equações diferenciais), microparâmetros de transferência de energia e probabilidades de decaimento radiativo, entre outros. Identificamos dois mecanismos de depolução da região do infravermelho, a migração de energia e a conversão ascendente, e dois mecanismos de população dos níveis 4S3/2 e 4F9/2, a absorção do estado excitado e a conversão ascendente por transferência de energia. A análise dos resultados indicou que a conversão ascendente por transferência de energia é o principal mecanismo de população dos níveis 4S3/2 e 4F9/2 / Given the need of integrated devices, as microchip laser and optical inverter, for instance, spectroscopic studies on samples with large ion doping concentrations are necessary. However, the use of highly doped samples brings with it the problem of luminescence quenching due to intense energy transfer processes. Therefore, in the present work we studied the energy transfer processes that diminish the infrared luminescence in two fluoride glass compositions (fluoroindate and fluorozircoaluminate) doped with Er+3 in the range of 0.1 to 20% molar. For that, we obtained energy transfer parameters using rate equations formalism for Er+3 energy levels. We also obtained the microscopic parameters of energy transfer, and radiative decay rates, among others. Two mechanisms of depopulation of level 4I11/2 were identified, energy migration and up conversion. Similarly the mechanisms responsible for the population of levels 4S3/2 and 4F9/2, were identified as excited state absorption and energy transfer up conversion. The results analysis indicates that the energy transfer up conversion is the major mechanism for the population of levels 4S3/2 and 4F9/2.

Orientador: Teresa Dib Zambon Atvars / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-20T16:58:27Z (GMT). No. of bitstreams: 1 Bonon_BrunaMediciAmorim_M.pdf: 3494663 bytes, checksum: 8ebdcfe3c6777860773199ca2b85e29d (MD5) Previous issue date: 2012 / Resumo: Nesse trabalho, foram estudadas as propriedades fotofísicas de misturas entre dois polímeros fluorescentes (PVK e PFO-MEHPV) em solução e em filmes com diferentes concentrações dos dois componentes. O polímero PVK pode atuar como doador de energia para o polímero PFO-MEHPV que consequentemente é intitulado de receptor. Há uma forte sobreposição espectral entre o espectro de emissão do doador e o espectro de absorção do receptor, além disso, o doador (PVK) possui um componente de tempo de vida de fluorescência longo. Esses dois fatores somados podem favorecer o processo não-radiativo de transferência de energia (FRET, fluorescence resonance energy transfer). Nos estudos em solução, os espectros de fotoluminescência do PVK mostraram uma diminuição da intensidade de emissão desse polímero na presença do PFO-MEHPV. Entretanto, o tempo de vida não praticamente não se alterou com o aumento da concentração do doador nas misturas. Dessa forma, pode-se concluir que para as soluções a diminuição da intensidade da emissão do doador está mais correlacionada com a transferência de energia trivial do que com FRET pelo mecanismo de Föster. Por outro lado, as blendas poliméricas no estado sólido parecem submeter-se mais eficientemente ao processo de transferência de energia do tipo Föster, pois os resultados demonstraram que houve tanto a diminuição da intensidade de emissão do doador quanto a diminuição do tempo de vida do mesmo. Além disso, ao se excitar uma das blendas com um comprimento de onda adequado somente para o doador, obteve-se também a emissão do receptor. Isso evidencia a transferência de energia do doador para o receptor. As alterações dos dados fotofísicos com a composição das blendas se correlacionam com as alterações nas correspondentes morfologias dos filmes, analisadas por microscopia eletrônica de varredura / Abstract: The energy transfer processes were studied for mixtures of PVK and PFO-MEHPV, which are two polymers that have a strong overlap between the donor emission spectrum and the acceptor absorption spectrum, in both solutions and films and with several relative proportions of the two components. The emission decay of neat PVK is much slower than that of PFO-MEHPV, which may favor the non-radiative energy transfer process. The steady-state PL spectra of PVK exhibited an intensity decrease in the presence of PFO-MEHPV, but the decrease in the the PVK lifetime does not follow the same trend upon increasing the donor concentration. Thus, it has been assumed that the intensity decrease was more strongly correlated with the trivial energy transfer than with FRET process by the Föster mechanism. The low FRET efficiency may be attributed to the presence of several types of the others PVK photophysical processes that quench the excited state via FRET process. Nevertheless, the solid-state polymer blends undergo Förster-type energy transfer more efficiently in addition to the trivial process, as demonstrated by the relative increase in the emission intensity of the acceptor following the donor excitation and the decrease in the donor PL lifetime. Moreover, in films, there are two concentration ranges in which the donor lifetime exhibited an additional decrease, and these concentration ranges are coincident with those at which changes in the morphology were observed using SEM / Mestrado / Físico-Química / Mestre em Química

Photosynthesis involves the absorption of photons by light-harvesting pigments and the subsequent transfer of excitation from the absorption centre to the reaction centre. This highly efficient phenomenon of excitation transfer has traditionally been explained by the Forster mechanism of incoherent hopping of excitation from one chromophore to another. Recently 2D electronic spectroscopic evidences were gathered by Fleming and coworkers on the photosynthetic Fenna-Matthews-Olson (FMO) complex in green sulfur bacteria [1]. Subsequent simulation studies by the same group [2] led to the proposition of a quantum-mechanical, coherent, wave-like transfer of excitation among the chromophores. However, Fleming's conclusions regarding retention of coherence appeared surprising because, the complex would interact with the numerous degrees of freedom of the protein scaffold surrounding it, leading to decoherence, which is expected to be rapid. Thus, we were interested in proposing an analytical treatment to rationalize the excitation transfer. Traditional approaches employed for studying excitation energy transfer involve the master equation techniques where the system-bath coupling is perturbative and is truncated after a few orders. It is important to note that the system-bath coupling causes both decoherence and population relaxation. Such a perturbative approximation is difficult to justify for the photosystem, as the system-bath coupling and the interchromophoric electronic coupling have comparable values. Also, these treatments are largely numerical studies and demand involved calculations. Thus, exact calculations for such a system (7-level) are very difficult. Consequently, we were interested in developing an analytical approach where the coupling is treated as non-perturbative. We devised a novel analytical treatment which employs a unitary transformation analogous to the one used for the theory of nonadiabatic effects in chemical reactions [3]. Our treatment rests on an adiabatic basis which are eigenstates calculated at each nuclear position (i.e. at each configuration of the bath) bearing a parametric dependence in Qi, where Qi denotes the shift of the exciton at site `i' due to the environment. The treatment is justified because in the case of coherent transfer, the excitation would travel mostly amongst the adiabatic states and the effects of non-adiabaticity are small. We observed that the system-bath coupling, after the unitary transformation, could be decoupled at the lowest order into two parts: a) an adiabatic contribution, which accounts solely for decoherence (this is evaluated almost exactly in our approach) and b) a non-adiabatic contribution which accounts for population relaxation from one adiabatic state to another (treated by a Markovian master equation). When we applied our technique to the FMO complex, our prediction for population evolution at the chromophores showed excellent correspondence with those obtained by Nalbach and coworkers using path-integral calculations [4], which are exact. These were calculations where the environment was modelled using a Drude spectral density. Our method allowed the calculations to be readily performed for different temperatures as well. It should be specifically emphasized that, unlike the involved and cumbersome path-integral calculations by Nalbach and coworkers [4] or the hierarchical equation calculations by Ishizaki et al. [2], our method is simple, easy to apply and computationally expedient. Further it became evident that the ultra-efficiency of energy transfer in photosynthetic complexes is not completely captured by coherence alone but is the result of an interplay of coherence and the dissipative influence of the environment (also known as ENAQT or Environment Assisted Quantum Transport [5]). An added advantage of our analytical treatment was the flexibility it offered. Thus, we could use our formalism to perform expedient analyses on the behavior of the system under various conditions. For example, we may wish to evaluate the consequences of introducing correlations among the bath degrees of freedom on the efficiency of transfer to the reaction centre. To this end, we applied our formalism by introducing correlations among the bath degrees of freedom and then by introducing anticorrelations among the bath degrees of freedom. The conclusions were interesting, for they suggested that the efficiency of transfer to the reaction centre was enhanced by the presence of anti-correlations, when compared with an uncorrelated bath. Uncorrelated baths, in turn, had a higher efficiency of energy transfer than correlated baths [6]. Thus, the population evolution is fastest for the anti-correlated bath, followed by the uncorrelated bath and is slowest for the correlated bath. Similar conclusions have been reached at by Tiwari et al. [7]. We could also extend the formalism for studying the system under different spectral densities for the environment, apart from just the Drude spectral density which is popularly used in literature associated with FMO calculations. For instance, the FMO system could be analyzed for the Adolphs-Renger spectral density [3, 8]. Once again our results showed excellent agreement with those reported by Nalbach. We also analyzed the FMO system under the spectral density proposed by Kleinekathofer and coworkers [9]. It was found that these latter spectral densities had more profound participation from the environment, therefore coherences were destroyed more effectively and population relaxation was faster. The excitation transfer to the final site (site closest to the reaction centre in the FMO complex) was found to be faster for the Adolphs and Renger spectral density and the spectral density proposed by Kleinekathofer and coworkers, when compared to the Drude spectral density. Also, the excitation transfer was fastest when we modelled the environment using the Kleinekathofer spectral density. This reinforced the previous conclusions that the dissipative effects of the environment promote a faster energy transport. Being an almost analytical approach, our technique could be applied to systems with larger number of levels as well. A good example of such a case is the MEH-PPV polymer. 2D electronic-spectroscopic experiments performed on this polymer in solution speculate that the excitation energy transfer might be coherent even at physiological temperatures [10]. A prototype for studying this system might be a conjugated polymer with around 80-100 chromophores. Linewidths and Lineshapes in the vicinity of Graphene It has been reported that a vibrating dipole may de-excite by transferring energy non-radiatively to a neighboring metal surface [11]. It is also understood that due to its delocalized pi-cloud, graphene has a continuum of energy states and can behave like a metal sheet and accept energies. Thus, we proposed that if a vibrationally excited dipole de-excites in the vicinity of a graphene sheet, graphene may get electronically excited and thus serve as an effective quencher for such vibrational excitations. Depending on the distance of the dipole from the graphene sheet, the transfer might be intense enough to be spectroscopically probed. We have investigated the rate of such an energy transfer. We use the Dirac cone approximation for graphene, as this enables us to obtain analyt-ical results. The Fermi Golden rule was used to evaluate the rate of energy transfer from the excited dipole to the graphene sheet [12]. The calculations were performed for both the instances: a) energy transfer from a dipole to undoped graphene and, b) energy trans-fer from a dipole to doped graphene. For undoped graphene, the carrier (electron) charge density in the conduction band is zero and we would only have transitions from the valence band to the conduction band. As a consequence of absence of carrier charge density in CB (conduction band), the screening of Coulombic interactions in the graphene plane is ineffective. Thus, one could use the non-interacting polarizability for undoped graphene in the rate expression [13]. However, when we consider the case of doped graphene where EF is shifted upwards into CB, the conduction band electrons will contribute to screening. In this case, we have two sets of transitions: a) from ki in VB (valence band) to kf in CB and b) ki in CB to kf in CB, where ki and kf are the wavevectors which correspond to the initial and final electronic states in graphene. So we have used the polarizability propagator in the random phase approximation [14] to calculate the rate following the approach of [13]. It is also known that the imaginary part of the frequency domain dipole-dipole corre-lation function is a measure of the lineshape [15]. We were, thus, interested in evaluating the lineshape for these transitions. For evaluating the correlation function, we used the partitioning technique developed by L•owdin [16] and subsequently extracted the lineshape from its imaginary part. Using this method, we calculated lineshape for the vibrational excitation of CO molecule in the vicinity of an undoped graphene lattice. The linewidth for this system also was obtained. It could be seen that the vibrational linewidth for 1 CO in the vicinity (5 A) of undoped graphene (EF = 0:00eV ) is small (0:012 cm ) but could be observed experimentally. The lineshape calculations were also extended to cases where it is possible to have atomic transitions by placing an electronically excited atom in the vicinity of the graphene sheet. We considered the following two cases: a) 3p ! 2s transition in hydrogen atom, at a distance of 12 A from the graphene sheet and, b) 4p ! 3s transition in hydrogen atom, at a distance of 20 A from the graphene sheet. The linewidths for atomic transitions could be easily probed in these cases ( 55 cm 1 for 3p ! 2s and 56 cm 1 for 4p ! 3s). In the preceding calculations, the transi-tion dipoles were considered perpendicular to the graphene surface. It is worthwhile to note that if the transition dipoles are considered parallel to the graphene surface, the respective linewidths would be half of those obtained for the case where the transition dipoles are perpendicular. Another interesting possibility would be to consider a lanthanide metal complex placed within a few nanometers from graphene. Lanthanides are known to have sharp f-f transitions [17] and consequently, one could easily observe the effects of broadening due to energy transfer to the electronic system of graphene. Energy Eigenmodes for arrays of Metal Nanoparticles In the final part of the thesis we consider organized assemblies of metal nanoparti-cles, specifically helical and cylindrical assemblies and investigate the plasmonic excitation transfer across these assemblies. These were motivated by recent studies which reported growth of chiral asymmetric assemblies of nanoparticles on D and L- isomers of dipheny-lalanine peptide nanotubes [18]. The plasmons in the helical/cylindrical assemblies are expected to couple with each other via electromagnetic interactions. We construct the Hamiltonian for such systems and evaluate the eigenmodes and energies pertaining to these modes in the wave vector space. We also perform calculations for the group velocity for each eigenmode as this gives us an idea of which eigenmode transports excitation the fastest.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21190号 / エネ博第364号 / 新制||エネ||71(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 佐川 尚, 教授 森井 孝, 教授 松田 一成 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

Broiler production requires significant expenditures for heating fuel year round. Poor thermal envelope performance leads to reduced live performance, increased energy use, and reduced profitability. Poultry house building component thermal resistance (R-value) is subject to change over time. To characterize the thermal envelope heat transmission and building component R-value of two broiler houses of different ages, conductive heat flux (W/m2) and temperature gradient (Delta T °C) were monitored with heat flux meter (HFM) arrays and temperature sensors over a 13-month period. Net heat loss and building component (walls and ceiling) thermal resistance were determined from the data. Results showed differences in net heat loss were observed for the ceiling zones where 84% more heat was lost through the ceiling of the older house than that of the newer house (P < 0.05). R-values determined from field measurements for both houses were below estimated theoretical composite R-values. Observed R-values were greater for ceiling envelope zones of the newer house when compared to the older house. Increased heat loss and reductions in ceiling envelope zone R-values for the older house were attributed to shifting and settling of the looseill cellulose attic insulation material, which was especially prevalent at the ceiling peak zone. To verify the feasibility of using sol-air temperature in lieu of outside air temperature to account for radiant load during warm conditions, field measurements of temperature (°C) (interior air, exterior air, and exterior surface) and solar radiation (W/m2) were recorded of a broiler house. Sol-air temperatures were calculated from these data. Observed maximum daily air temperatures were significantly different (P<0.0001) from maximum surface and sol-air temperatures. Maximum surface and sol-air temperatures were not significantly different (P=0.2144, P=0.1544). Simulations of conductive heat transfer by air and sol-air temperatures using climatic data showed heat gain as calculated by sol-air Delta T was considerably higher when compared to heat gain calculated by air Delta T. This study supports the rationale that the sol-air temperature concept results in improved estimates of conductive heat transfer during daytime conditions which can be used to optimize insulation and ventilation requirements for broiler houses during warm conditions.