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Previous issue date: 2017-12-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Os molibdatos v?m sendo objeto de estudos devido as suas diversas aplica??es. Entre os molibdatos, o molibdato de b?rio (BaMoO4) e molibdato de zinco (ZnMoO4) t?m se destacado pelas suas interessantes propriedades fotoluminescentes, com emiss?es de luz na regi?o do azul, verde e laranja, e pelos seus diferentes m?todos de obten??o, como hidrotermal, sol-gel e coprecipita??o. P?s de Ba1-xZnxMoO4 (x=0; 0,25; 0,50; 0,75 e 1) foram sintetizados, em etapa ?nica, pelo m?todo de spray pir?lise ultrass?nico, utilizando temperaturas de 1000 ?C e 1100 ?C. O tempo para forma??o das part?culas dentro do reator foi de aproximadamente 1 min. As amostras foram caracterizadas estruturalmente pela t?cnica de difra??o de raios X e morfologicamente pela t?cnica de microscopia eletr?nica de varredura de emiss?o de campo (MEV-FEG). As propriedades ?pticas das amostras foram estudadas utilizando as espectroscopias de UV-vis?vel e de fotoluminesc?ncia (FL). Os padr?es de DRX mostraram que as amostras com x = 0 e x = 1 t?m estrutura cristalina scheelita tetragonal e tricl?nica, respectivamente, sem a presen?a de fases secund?rias. Por outro lado, as amostras com x = 0,25, 0,50 e 0,75 revelaram a forma??o de uma heteroestrutura tetragonal/tricl?nica, em que ocorre substitui??o at?mica de Ba2+ por Zn2+ na estrutura tetragonal do BaMoO4 e na estrutura tricl?nica do ZnMoO4 ocorrendo a substitui??o at?mica de Zn2+ por Ba2+. As micrografias de MEV-FEG demostraram que as part?culas obtidas t?m morfologia predominantemente esf?rica, com di?metros que variam entre 100 e 1500 nm. A energia de gap dos Ba1-xZnxMoO4 variou entre 4,56 eV ? 4,17 eV, com os p?s com x = 0 se obteve os valores mais elevados (4,54 eV e 4,56 eV) e os p?s com x = 1 os valores mais baixos (4,17 eV e 4,26 eV). Dessa forma, foi percebido que as energias de gap das amostras diminuem com o aumento do valor de x, ou seja, com aumento da substitui??o dos ?tomos de Ba2+ pelos de Zn2+. Os espetros fotoluminescentes (FL) das amostras apresentaram comportamento banda larga, com emiss?o predominante na regi?o laranja-vermelho e pequena contribui??o de emiss?o da regi?o azul-verde, com a amostra de x = 0,75 obtida ? 1000 ?C mostrando maior intensidade FL. As coordenadas de cromaticidade x e y mostraram que as amostras com x ? 0,75 apresentam emiss?o em laranja, entretanto, as amostras com x = 1 apresentaram emiss?o em branco, podendo ser um candidato promissor para aplica??es em diodos emissores de luz. / The molybdates have been the subject of studies due to their various applications. Among the molybdates, the barium molybdate (BaMoO4) and zinc molybdate (ZnMoO4) have been standing out by its interesting photoluminescent properties, with light emissions in the region of the blue, green and orange, and by its different methods of obtaining, such as hydrothermal, sol-gel and coprecipitation. Ba1-xZnxMoO4 (x = 0, 0.25, 0.50, 0.75 and 1) powders were synthesized, in a one-step, by the ultrasonic spray pyrolysis method, using temperatures of 1000 ?C and 1100 ?C. 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, the samples with x = 0.25, 0.50 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+. FESEM micrographs showed that the particles obtained have predominantly spherical morphology with diameters ranging from 100 to 1500 nm. The gap energy of the Ba1-xZnxMoO4 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. 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, with the sample of x = 0.75 obtained at 1000 ? C showing higher PL intensity. 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, can be a promising candidate for applications in light emitting diodes.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/24819 |
| Date | 18 December 2017 |
| Creators | Santiago, Anderson de Azevedo Gomes |
| Contributors | 27816279841, Godinho J?nior, M?rio, 17876195830, Motta, Fabiana Villela da, Delmonte, Mauricio Roberto Bomio |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM CI?NCIA E ENGENHARIA DE MATERIAIS, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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