Banca de DEFESA: HELDER MOREIRA BRAGA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : HELDER MOREIRA BRAGA
DATA : 30/04/2020
HORA: 14:00
LOCAL: Santo André
TÍTULO:

Synthesis, Optical Properties and Functionalization of Perovskite Quantum Dots of CsPbX3 Halides

PÁGINAS: 83
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Prop. Óticas e Espectrosc. da Mat. Condens; Outras Inter. da Mat. com Rad. e Part.
RESUMO:

Micro and nanostructured semiconductor systems of transition metal oxides and halide perovskites have been of great interest due to their important physical properties and potential applications. These materials when obtained in the form of Quantum Dots (QDs) attract great attention, due to their peculiar optical properties, which make them very interesting in nanotechnology applications, such as light emitting diode, solar cells, and photocatalysis. In this work, oxide microfoils, microwires, and microtubes of transition metals with nanostructured surfaces, such as ZnO, Fe₂O₃, TiO₂ and NiO, were synthesized through the thermal oxidation process. On the other hand, halides perovskites of the CsPbX₃ family were also synthesized, where X = (Cl, Br, I) in the form of QDs. The colloidal QDs solution was obtained by the hot injection method and by the supersaturated recrystallization technique at room temperature. Photoluminescence (PL) measurements indicated a pronounced, narrow emission peak at 405 nm, 505 nm, and 684 nm, resulting in a band gap energy of 2.99 eV, 2.43 eV, and 1.73 eV for QDs of CsPbCl₃, CsPbBr₃ and CsPbI₃, respectively. The results of UV-Vis absorption spectroscopy corroborate with the results of QD emission. Measures of time-resolved PL revealed distinct lifetimes for QDs with great influence of defect-related states. Transmission electron microscopy images indicated CsPbBr₃nanocrystals in the form of parallelepipeds with sides of ~ 19.0 ± 0.7 nm and ~ 9.0 ± 0.6 nm. Scanning electron microscopy (SEM) images revealed abrupt coalescence leading to the formation of microsticks for the CsPbI₃ sample. Subsequently, the QDs were deposited on the surface of Fe₂O₃/Fe₃O₄ magnetic microtubes. Structural and morphological characterizations confirmed the adherence of perovskite nanocrystals on the surface of the nanostructured magnetic oxide. Electrical resistivity measurements in the magnetic microtubes revealed a strong interaction with the decorated nanocrystals forming local nanoheterostructures. It is suggested that this strong interaction is revealed by increasing the electrical conductivity of the microtube due to charge transfer from nanocrystals. Measurements of time-resolved photoluminescence in Fe₂O₃/Fe₃O₄ microfoils decorated with CsPbBr₃ QDs indicated a difference in the recombination dynamics of free carriers and excitons, in addition to the defect-related states. These results corroborate the formation of chemically interacting local nanoheterostructures with the electric charge transfer which gives extra functionality to the photoluminescent and magnetic microtube.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 2605463 - JOSE ANTONIO SOUZA
Membro Titular - Examinador(a) Externo ao Programa - 3066318 - JULIAN ANDRES MUNEVAR CAGIGAS
Membro Titular - Examinador(a) Externo à Instituição - RAFAEL SA DE FREITAS - USP
Membro Suplente - Examinador(a) Externo ao Programa - 1652541 - LETICIE MENDONCA FERREIRA
Membro Suplente - Examinador(a) Externo à Instituição - MARCIO PERON FRANCO DE GODOY - UFSCAR