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| Author(s): |
Arthur Aló de Oliveira
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2022-01-12 |
| Examining board members: |
Lázaro Aurélio Padilha Junior;
Francisco das Chagas Marques;
Marcelo Gonçalves Vivas
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| Advisor: | Lázaro Aurélio Padilha Junior |
| Abstract | |
Nanocrystals have been one of the most studied materials for optical applications, as they offer several unique electronic and optical properties due to their nanometric size. These properties include tunable bandgap, allowing for customized emission and absorption spectra, and control of multiexciton and multiphoton interactions. This way, this type of nanomaterial has become an important platform for nonlinear optics research and applications. Many of the optical properties of nanocrystals are coupled to their size, including the photoluminescence emission peak, Auger recombination lifetime and linear and nonlinear absorption cross sections. In this project we set out to explore how the multiphoton absorption of CdSe-base nanocrystals is affected by different heterostructures. These include quantum dots with different shelling materials, causing different band alignments for each one. However, as we first explored the most used techniques on the literature for nonlinear absorption characterization, we realized that the typical estimated error values for these experiments would be a limiting factor for a comparative study between samples. Therefore, in this work we introduce a new characterization method for the multiphoton absorption cross section of nanocrystals, called Multi-Photon Absorption by Photoluminescence Saturation (MPAPS). We measured the two-photon absorption (2PA) cross section of three types of CdSe-base nanostructures: CdSe core only, CdSe/ZnCdS type I core/shell and CdSe/CdS quasi-type II core/shell. The core/shell samples were measured in sets of fixed core size and variable shell thickness. We compared the volume dependence of the 2PA cross section of all samples and found that the studied heterostructures generally present a lower scaling with volume than the core only. We rationalize these results with a simple 2PA model that considers the lower overlap between wavefunctions caused by the heterostructures. Furthermore, we also measured the three-photon absorption (3PA) cross section of a group of the samples, where we observed an even lower dependence with the volume for the type I core/shell samples when compared to the core only (AU) | |
| FAPESP's process: | 19/22823-5 - Two-photon processes in quantum confined semiconductors |
| Grantee: | Arthur Aló de Oliveira |
| Support Opportunities: | Scholarships in Brazil - Master |