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Advanced spectroscopic characterization of quantum dot ensembles
Greben, Michael ; Valenta, Jan (advisor) ; Linnros, Jan (referee) ; Vácha, Martin (referee)
Title: Advanced spectroscopic characterization of quantum dot ensembles Author: Michael Greben Department: Department of Chemical Physics and Optics Supervisor of the doctoral thesis: Prof. Jan Valenta, Ph.D. Abstract: Semiconductor quantum dots (QDs) are small crystallites whose sizes (of the order of nm) cause spatial confinement of carriers in all 3 dimensions. As result, QDs often reveal very different physical properties in comparison with their bulk counterparts. From the optical point of view, the broadening of bandgap with QD-size shrinking is particularly interesting. It is a purely quantum mechanical effect that results from quantum confinement (QC), i.e. dimensional limitations of excitons. A strong spatial confinement leads to a relaxation of momentum (Heisenberg uncertainty principle), consequently, larger overlap of the wave-functions of carriers results in significant increase of probability of radiative recombination. Therefore ensembles of QDs are promising candidates for new generations of photonic and photovoltaic devices. This PhD thesis is primary focused on detailed spectroscopic characterization of ensembles of direct (PbS) and indirect (Si) semiconductor QDs in both colloidal (toluene) and matrix-embedded (oxide or oxinitrides multilayers) forms. The oleic- acid capped PbS QDs were...
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Advanced spectroscopic characterization of quantum dot ensembles
Greben, Michael ; Valenta, Jan (advisor)
Title: Advanced spectroscopic characterization of quantum dot ensembles Author: Michael Greben Department: Department of Chemical Physics and Optics Supervisor of the doctoral thesis: Prof. Jan Valenta, Ph.D. Abstract: Semiconductor quantum dots (QDs) are small crystallites whose sizes (of the order of nm) cause spatial confinement of carriers in all 3 dimensions. As result, QDs often reveal very different physical properties in comparison with their bulk counterparts. From the optical point of view, the broadening of bandgap with QD-size shrinking is particularly interesting. It is a purely quantum mechanical effect that results from quantum confinement (QC), i.e. dimensional limitations of excitons. A strong spatial confinement leads to a relaxation of momentum (Heisenberg uncertainty principle), consequently, larger overlap of the wave-functions of carriers results in significant increase of probability of radiative recombination. Therefore ensembles of QDs are promising candidates for new generations of photonic and photovoltaic devices. This PhD thesis is primary focused on detailed spectroscopic characterization of ensembles of direct (PbS) and indirect (Si) semiconductor QDs in both colloidal (toluene) and matrix-embedded (oxide or oxinitrides multilayers) forms. The oleic- acid capped PbS QDs were...
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Comparison of drought effect on young coppiced and standard individuals of sessile oak
Stojanović, Marko ; Čater, M. ; Pokorný, Radek
Assimilation and photosynthetic efficiency (quantum yield) of young oaks were compared in coppice and standard sessile oak stands of comparable age (100-120 years) under different light intensity categories. Measurements of assimilation response were performed during three consecutive growing seasons (2012, 2013 and 2014). In every category 8 young oaks of generative origin and same number of coppice sprouts of different stool were measured. The quantum yield in optimal conditions in standards was highest in the category A of closed canopy, while in coppices in category C. During severe drought in 2013 the drop in efficiency of standards was evident in all categories, while in coppices no differences in efficiency were confirmed between optimal and drought stress, proving the advantage of young coppices over standards.
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Methods of Study of Photosensitizer-Photophysics with Application on Thiazolyl-porphyrins
Scholz, Marek
Title: Methods of Study of Photosensitizer-photophysics with Application on Thiazolyl-porphyrins Author: Marek Scholz Department: Department of Chemical Physics and Optics Supervisor: RNDr. Roman Dědic, Ph.D. Supervisor's e-mail address: Roman.Dedic@mff.cuni.cz Abstract: Photodynamic therapy for oncologic and various chronic diseases is a rapidly emerging method of treatment. It is based on the production of highly reactive singlet oxygen and free radicals by excitation energy transfer from the molecules of photosensitizers. Photosensitizers are preferentially accumulated in the target tissues and locally illuminated. This way produced reactive species cause apoptosis or necrosis of the cells leading to the desired therapeutic effect. Synthesis and subsequent photophysical characterization of photosensitizing dyes is a fundamental part of the development of photodynamic methods. The main aim of the work is to explain the most widely used methods of photophysical study of photosensitizers and apply them to new synthesized photosensitizers: thiazolyl-porphyrins. Methods of absorption and fluorescence spectroscopy, flash- photolysis, time- and spectral-resolved detection of luminescence, optoacoustic spectroscopy and other spectroscopic methods were used. Thiazolyl-porphyrins proved to be promising new...
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Methods of Study of Photosensitizer-Photophysics with Application on Thiazolyl-porphyrins
Scholz, Marek ; Dědic, Roman (advisor) ; Hála, Jan (referee)
Title: Methods of Study of Photosensitizer-photophysics with Application on Thiazolyl-porphyrins Author: Marek Scholz Department: Department of Chemical Physics and Optics Supervisor: RNDr. Roman Dědic, Ph.D. Supervisor's e-mail address: Roman.Dedic@mff.cuni.cz Abstract: Photodynamic therapy for oncologic and various chronic diseases is a rapidly emerging method of treatment. It is based on the production of highly reactive singlet oxygen and free radicals by excitation energy transfer from the molecules of photosensitizers. Photosensitizers are preferentially accumulated in the target tissues and locally illuminated. This way produced reactive species cause apoptosis or necrosis of the cells leading to the desired therapeutic effect. Synthesis and subsequent photophysical characterization of photosensitizing dyes is a fundamental part of the development of photodynamic methods. The main aim of the work is to explain the most widely used methods of photophysical study of photosensitizers and apply them to new synthesized photosensitizers: thiazolyl-porphyrins. Methods of absorption and fluorescence spectroscopy, flash- photolysis, time- and spectral-resolved detection of luminescence, optoacoustic spectroscopy and other spectroscopic methods were used. Thiazolyl-porphyrins proved to be promising new...
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