Browsing by Subject "Confinement"

Now showing 1 - 3 of 3

Open Access
Attractive versus repulsive excitonic interactions of colloidal quantum dots control blue-to red-shifting (and non-shifting) amplified spontaneous emission
(American Chemical Society, 2013-11-21) Cihan, A. F.; Kelestemur, Y.; Guzelturk, B.; Yerli, O.; Kurum, U.; Yaglioglu, H. G.; Elmali, A.; Demir, Hilmi Volkan
Tunable, high-performance, two-photon absorption (TPA)-based amplified spontaneous emission (ASE) from near-unity quantum efficiency colloidal quantum dots (CQDs) is reported. Besides the absolute spectral tuning of ASE, the relative spectral tuning of ASE peak with respect to spontaneous emission was shown through engineering excitonic interactions in quasi-type-II CdSe/CdS core/shell CQDs. With core shell size adjustments, it was revealed that Coulombic exciton-exciton interactions can be tuned to be attractive (type-I-like) or repulsive (type-II-like) leading to red- or blue-shifted ASE peak, respectively, and that nonshifting ASE can be achieved with the right core shell combinations. The possibility of obtaining ASE at a specific wavelength from both type-I-like and type-II-like CQDs was also demonstrated. The experimental observations were supported by parametric quantum-mechanical modeling, shedding light on the type-tunability. These excitonically engineered CQD-solids exhibited TPA-based ASE threshold as low as 6.5 mJ/cm(2) under 800 nm excitation, displaying one of the highest values of TPA cross-section of 44 660 GM.
Open Access
Evaluation of spaciousness in isolated and confined environments
(2023-12) Diker, Berk
This thesis explores the adverse psychological effects of Isolated, Confined, and Extreme (ICE) environments, aiming to explore the correlation between these effects and interior architectural elements. In addition, several methods are tested to evaluate interior architectural elements that may directly impact the perceived spaciousness of these environments. The initial phase of the thesis examined the effects of the COVID-19 pandemic on the perception of interior spaces. Individuals who found their living spaces visually appealing, engaged in various activities, expressed satisfaction with their connections to outdoor spaces, encountered less boredom, and displayed fewer signs of anxiety and psychological distress. The following phase explored the effects of furniture, lighting, surface texture, and ceiling height on spaciousness perception and surveyed emotional and aesthetic responses to various design factors. The results indicated that interior architectural elements have a relatively minor impact on individuals' spatial perception within a habitat. Design training is a more significant influencer in all spatial evaluations than interior architectural elements. Although furniture, lighting, and texture have statistically significant effects on spaciousness and aesthetic judgments, design training remains a substantial moderator of these effects. This research contributes substantially to comprehending the complex dynamics between interior architectural design and human perception. The findings underscore the profound influence of design choices on practical functionality and emotional experiences within confined spaces. The study's implications extend to architects, designers, and policymakers, providing valuable insights for enhancing psychological well-being in ICE environments.
Open Access
Self-consistent computation of electronic and optical properties of a single exciton in a spherical quantum dot via matrix diagonalization method
(American Institute of Physics, 2009-08-21) Sahin, M.; Nizamoglu, S.; Kavruk, A. E.; Demir, Hilmi Volkan
In this study, we develop and demonstrate an efficient self-consistent calculation schema that computes the electronic structure and optical properties of a single exciton in a spherical quantum dot (QD) with an interacting pair of electron and hole wave functions. To observe modifications on bands, wave functions, and energies due to the attractive Coulomb potential, the full numeric matrix diagonalization technique is employed to determine sublevel energy eigenvalues and their wave functions in effective mass approximation. This treatment allows to observe that the conduction and valance band edges bend, that the electron and hole wave functions strongly localize in the QD, and that the excitonic energy level exhibits redshift. In our approach for the Coulomb term between electron and hole, the Poisson-Schrodinger equations are solved self-consistently in the Hartree approximation. Subsequently, exciton binding energies and associated optical properties are computed. The results are presented as a function of QD radii and photon energies. We conclude that all of these numerical results are in agreement with the experimental studies.