Banca de DEFESA: ANDERSON DE AZEVEDO GOMES SANTIAGO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : ANDERSON DE AZEVEDO GOMES SANTIAGO
DATA : 18/12/2017
HORA: 14:00
LOCAL: Auditório do CCET
TÍTULO:

Characterization of the photoluminescent properties of Ba1-xZnxMoO4 synthesized by the ultrasonic pyrolysis spray method

PALAVRAS-CHAVES:
PÁGINAS: 80
GRANDE ÁREA: Engenharias
ÁREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
ESPECIALIDADE: Cerâmicos
RESUMO:

Ba_1-xZn_xMoO₄ (x = 0, 0.25, 0.5, 0.75 and 1) powders were synthesized, in a one-step, by the ultrasonic spray pyrolysis method, using temperatures of 1000 ºC and 1100 ºC. Time for particle formation within the reactor was approximately 1 min. The samples were structurally characterized by the X-ray diffraction and morphologically by the field emission scanning electron microscopy (FESEM). Optical properties of the samples were studied using UV-visible and photoluminescence (PL) spectroscopies. The DRX patterns showed that the samples with x = 0 and x = 1 have crystalline tetragonal scheelite and triclinic structure, respectively, without the presence of secondary phases. On the other hand, Rietveld refining of the DRX patterns of samples with x = 0.25, 0.5 and 0.75 revealed the formation of a heterostructure tetragonal/triclinic, in which atomic substitution of Ba²⁺ by Zn²⁺ in the tetragonal structure of the BaMoO₄ and triclinic structure of the ZnMoO₄ occurring the atomic substitution of Zn²⁺ by Ba²⁺, perceiving a slight increase portion of the tetragonal phase when the pyrolysis temperature increases. Thus, these modifications promote small structural distortions in these materials, being easily observed in the angles and edges of the base that delimit the tetrahedron [MoO₄] of these molybdates. FESEM micrographs showed that the particles obtained have predominantly spherical morphology with diameters ranging from 100 to 1500 nm. It was found that the primary particles forming microspheres of samples with x = 0 have high dimensions relative to the final size of microspheres, on the other hand for samples with x = 1 the primary particles exhibit low dimensions relative to microspheres. Thus, the decrease of the primary particles forming the microspheres was noted with the increase of x of Ba_1-xZn_xMoO₄, that is, with increase of the atomic substitution of Ba²⁺ by Zn²⁺. This fact is given by the difference in solubility of the barium and zinc precursor reagents, because solutes with a high degree of supersaturation, such as zinc nitrate, tend to form a larger number of crystallites of nanometric sizes. The gap energy of the Ba_1-xZn_xMoO₄ ranged from 4.56 eV to 4.17 eV, with the powders with x = 0, obtaining the highest values (4.54 eV and 4.56 eV) and the powders with x = 1 the lowest values (4.17 eV and 4.26 eV). In this way, it was noticed that the gap energies of the samples decrease with the increase of the value of x, that is, with increasing substitution of the Ba²⁺ for the Zn²⁺ atoms. Therefore, this phenomenon occurs due to atomic substitution raising the degree of disorder of the samples, increasing the intermediate intervals between the conduction and valence bands, which will result in the decrease of the gap band. Photoluminescent (PL) spectra of the samples showed broad band behavior, with predominant emission in the orange-red region and small emission contribution of the blue-green region. For samples with x = 0, the PL emission phenomenon is related to order-disorder degree of the [BaO₈] complexes and oxygen vacancies of the [MoO₄] complexes. For samples with x = 1, this phenomenon is related to the order-disorder degree of the [ZnO₆] complexes and oxygen vacancies of the [MoO₄] complexes. While, for samples with heterostructure tetragonal/triclinic, the PL emission is given by the degree of order-disorder and the charger transfer between the [BaO₈] and [ZnO₆] complexes, and oxygen vacancies of the [MoO₄] complexes. The chromaticity coordinates x and y showed that the samples with x ≤ 0.75 exhibit in orange emission, however, the samples with x = 1 presented white emission.

MEMBROS DA BANCA:
Interno - 1802888 - FABIANA VILLELA DA MOTTA
Externo à Instituição - MARIO GODINHO JUNIOR - UFG
Presidente - 1883170 - MAURICIO ROBERTO BOMIO DELMONTE