Banca de QUALIFICAÇÃO: ARTUR DE MORAIS

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
STUDENT : ARTUR DE MORAIS
DATE: 25/11/2020
TIME: 14:00
LOCAL: Google meet
TITLE:

Synthesis of Scheelite-type materials by Microwave-assisted Hydrothermal and its luminescence properties.

KEY WORDS:

Calcium Molybdate, Calcium tungstate, Microwave-assisted hydrothermal, photoluminescence.

PAGES: 46
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUMMARY:

Light emitting diodes (LEDs) have become the main form of lighting and light production, due to their great efficiency in relation to previous forms of lighting. One of the main ways to obtain white light for use in LEDs is to use devices that produce individual colors, being blue, green and red. Therefore, obtaining materials that emit these wavelengths is necessary. Scheelite-type materials have been the subject of study for decades due to their luminescent properties and ease of obtaining by various methods of synthesis. Among Scheelites, calcium tungstate and calcium molybdate present emissions in blue and green, respectively, in addition to being able to emit in red after doping with rare earths, in particular the europium. Calcium tungstate powders (CaWO₄), calcium molybdate (CaMoO4) and calcium tungstate doped with 1% europium (Ca_0.99WO₄: Eu_0.01) were synthesized by the microwave assisted hydrothermal method, using the processing times of 1, 2, 4 and 8 minutes. The samples were structurally characterized by the X-ray Diffraction (XRD) technique. The optical properties were characterized by the techniques of UV-visible and photoluminescence (PL). The diffractograms show that all the samples produced have the tetrahedral Scheelite structure and indicates that Eu³⁺ is incorporated by the calcium tungstate lattice without formation of secondary phase. The band gap values vary between 4.05 and 4.07 eV for CaMoO₄; 4.52 and 4.47 eV for CaWO₄ and 4.57 and 4.40 for CaWO₄:Eu. The processing time affects the values of the gaps due to their influence on the structure and morphology, factors directly linked to the presence of defects and energy levels within the gaps. The photoluminescence spectra show a broad band behavior for CaMoO₄ and CaWO₄ in the regions of greenish yellow and bluish green, respectively, with the highest intensities corresponding to CM8 and CW4 samples. The CW4 sample, in addition to being the most intense, presents a slight blue shift, but still present in the bluish green region. Europium doping is successful in shifting the emission of calcium tungstate to the direction of the red region, however the samples produced are located in the pink region of the diagram. The sharp peaks observed in the spectrum correspond to characteristic transitions of the europium.

BANKING MEMBERS:
Interna - 1802888 - FABIANA VILLELA DA MOTTA
Presidente - 1883170 - MAURICIO ROBERTO BOMIO DELMONTE
Externo à Instituição - RICARDO LUÍS TRANQUILIN - UFSCAR