Navegando por Autor "Lovisa, Laura Ximena"

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Evaluation of morphology and photoluminescent properties of PbMoO4 crystals by ultrasonic amplitude
(Springer, 2016-12-30) Paskocimas, Carlos Alberto; Gurgel, G. M.; Lovisa, Laura Ximena; Conceição, O. L. A.; Li, Maximo Siu; Silva, Elson Longo da; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
Lead molybdate (PbMoO4) crystals were synthesized by the facile sonochemical method at 20 kHz frequency with a variable ultrasonic amplitude and synthesis time. These crystals were structurally characterized by X-ray diffraction (XRD). Field emission scanning electron microscopy images were employed to observe the evolution of the crystal growth process. XRD patterns indicate that these crystals have a scheelite-type tetragonal structure. The growth mechanism of PbMoO4 crystal was proposed to explain the development stages starting with precipitates formed by particles with disordered growth to form dendritic structures. The effect of the amplitude processing applied was rather significant for the size range of the particles produced. The optical properties were analyzed by ultraviolet–Visible (UV–Vis) absorption spectroscopy and photoluminescence (PL) measurements. The spectrum shows that the sample has a typical green emission. The origin of the PL emission spectrum of the metal molybdates might be ascribed to the charge-transfer transitions within [MoO4] clusters
Fast and simultaneous doping of Sr0.9−x−y−zCa0.1In2O4:(xEu3+, yTm3+, zTb3+) superstructure by ultrasonic spray pyrolysis
(Elsevier, 2019-09) Paskocimas, Carlos Alberto; Santiago, Anderson de Azevedo Gomes; Lovisa, Laura Ximena; Medeiros, P. N.; Li, Maximo Siu; Carreño, Neftalí Lênin Villarreal; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In the present work, Sr0.9−x−y−zCa0.1In2O4:(xEu3+, yTm3+, zTb3+) particles were synthesized by the ultrasonic spray pyrolysis (USP) method to obtain a single-phase white phosphorus formed by six different cations in solution within the lattice (superstructure). The samples were also structurally and morphologically characterized by X-ray diffraction (XRD) techniques and by field emission scanning electron microscopy (FE-SEM). The photoluminescent behavior and the characteristics of the emitted colors were studied by the variation in the codoping of the rare earth elements. The Sr0.9Ca0.1In2O4 sample showed a near blue color emission, but all codoped samples showed emission in white with very close chromaticity coordinates to the standard white (x = 0.33 and y = 0.33). The Tm3+ → Tb3+ (ET1), Tm3+ → Eu3+ (ET2) and Tb3+ → Eu3+ (ET3) Energy Transfers were proposed and are considered necessary for adjusting and controlling the desired color properties
Fast photocatalytic degradation of an organic dye and photoluminescent properties of Zn doped In(OH)3 obtained by the microwave-assisted hydrothermal method
(Elsevier, 2014-11) Tavares, Marileide L.A.; Lovisa, Laura Ximena; Araújo, Vinícius Dantas; Silva, Elson Longo da; Li, Maximo Siu; Nascimento, Rubens Maribondo do; Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Crystalline zinc-doped indium hydroxide structures were prepared by the rapid and efficient microwave-assisted hydrothermal (MAH) method. X-ray diffraction (XRD), field emission gun-scanning electron microscopy (FEG-SEM), photoluminescence (PL) and UV–visible (UV–vis) spectroscopy were used to characterization the materials. FEG-SEM images revealed that pure In(OH)3 samples and Zn-doped samples exhibit nanocubic morphologies with a wide range of particle sizes. Relative intensities of PL emissions decreased as the Zn ion concentration increased from 0 to 4 mol%. UV–vis spectra indicate that Zn ion doping caused a band gap decrease with increased doping of 0% to 4% Zn, respectively, from 5.15 eV for 4.96 eV. Samples with Zn in the crystal lattice showed better photocatalytic activity and degradation of the RhB dye after 16 min of UV exposure
Growth mechanism and vibrational and optical properties of SrMoO4: Tb3+, Sm3+ particles: green– orange tunable color
(Springer, 2020-04-10) Santos, D. F. dos; Lovisa, Laura Ximena; Santiago, Anderson de Azevedo Gomes; Li, Maximo Siu; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
A SrMoO4 series co-doped with Tb3? and Sm3? was successfully prepared by the sonochemical method. The particles were characterized by X-ray diffraction, Raman spectroscopy, field emission gun scanning electron microscopy, UV–Vis spectroscopy and photoluminescence. Changes in SrMoO4: Tb3?, Sm3? morphologies were observed from an orderly growth of the particles. The mechanism of particle growth was proposed, indicating a hierarchical evolution of SrMoO4: Tb3?, Sm3? morphologies. The changes in emissions were evaluated by the effect of the dopants and their concentrations. Emissions were observed in white, green and orange according to the chemical composition of the samples. The SrMoO4 and SrMoO4: 1% Sm samples showed excellent results for CRI (79%) and LE ([ 310 lm/Wopt), thus indicating a material with potential for efficient white light emission
Influence of reaction temperature, proportions of iron, cobalt and KOH on the CoFe2O4 synthesis by hydrothermal method assisted by microwave heating
(Springer, 2017-06-19) Paskocimas, Carlos Alberto; Conceição, Ozivam Lopes de Aquino; Garcia, Laurênia Martins Pereira; Lovisa, Laura Ximena; Torres, M. M.; Soares, J. M.; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In this study, several factors such as reaction temperature, proportions of iron, cobalt and KOH were considered in the synthesis of cobalt ferrite nanoparticles by hydrothermal method assisted by microwave radiation. These parameters were studied using the full factorial experiment design. The effect of these factors on crystallite size was investigated using surface response methodology. The structure, crystallite size, magnetic properties, degree of inversion, as well as the chemical occupation of Fe ions were investigated in this study. The results indicated that all factors were statistically significant by analysis of variance (F-test), with a confidence level of 95%. The factors that influenced the growth of the crystallite were: KOH and iron concentration, precursors of cobalt salts and the effect of the interaction between the concentration of KOH and the concentration of precursors. The analysis of variance at a significance level of 95% indicates that the model adjusted to the experimental points is significant
Influence of the number of layers and crystallization temperature on the photocatalytic activity of Tio2 / In2 o3 thin films
(MedCrave Group, 2017-07-20) Paskocimas, Carlos Alberto; Garcia, Laurênia Martins Pereira; Gurgel, G. H. M.; Lovisa, Laura Ximena; Nascimento, Rubens Maribondo do; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
The TiO2/In2 O3 thin films were prepared by the spin coating method, varying their number of layers (4, 8 and 16 layers). The Method of polymerization of complex (CPM) was used to synthesize the precursor resins in order to produce thin films. The TiO2/In2 O3 films were heat–treated at 300°C, 500°C and 700°C and characterized by X–ray diffraction, scanning electron microscopy (FEG–SEM), atomic force microscopy (AFM), UV–vis spectrophotometer and photoluminescence (PL). It was found that the band gap energy of the as–prepared TiO2/In2 O3 composite thin films decrease as temperature increases. According to the UV–vis diffuse reflectance spectra, the TiO2/In2 O3 composite shows good visible–light absorption ability. The photoluminescent properties of the films were studied at room temperature using a wavelength of 350nm excitation. High photoluminescent intensity was observed for the films treated at 300°C heat, studied in different films. The photocatalytic activity of the composite TiO2/In2 O3 was evaluated by the hotodecomposition of methylene blue dye in aqueous solution and showed that all the composite samples presented excellent photocatalytic performance even when recycled. This study shows that the coupling of TiO2 with In2O3 is an effective way to increase the TiO2 absorption in the visible region for catalytic applications and that the temperature has a greater influence on the results than the number of layers
Influência do pH na morfologia do CuO obtido via método sonoquímico utilizando diferentes surfactantes
(Universidade Federal do Rio Grande do Norte, 2019-05-02) Oliveira, Patrícia Merlim de; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio; Lovisa, Laura Ximena
A indústria têxtil é considerada um dos maiores consumidores de água do mundo e os resíduos gerados no processo representam uma preocupante ameaça ao ecossistema devido aos poluentes orgânicos serem de difícil tratamento por métodos convencionais. Os processos oxidativos avançados (POAs) têm sido considerados uma técnica sustentável e eficiente para tratamento de águas residuais têxteis, nos quais os radicais hidroxila altamente reativos •OH são produzidos e dão origem ao processo de degradação oxidativa do corante, utilizando-se geralmente, um semicondutor sólido como catalisador. A alteração das propriedades de semicondutores convencionais são estudadas visando a otimização de suas propriedades. Neste trabalho, pós de óxido de cobre II (CuO) foram sintetizados via método sonoquímico utilizando diferentes surfactantes (PVP, PEG e EDA) variando o pH do meio em 8, 11 e 13. Os pós foram caracterizados por difração de raios-X (DRX), microscopia eletrônica de varredura por emissão de campo (MEV-FEG), método Brunauer-Emmett-Teller (BET), espectroscopia na região do UV-Visível (UV-Vis) e espectroscopia de infravermelho por transformada de Fourier (FTIR). Testes fotocatalíticos foram realizados para avaliação da aplicabilidade dos pós de CuO na degradação do corante azul de metileno. Os resultados da difração de raios-X mostraram que um aumento do pH de 8 para 13 favorece a formação de fase única de CuO, enquanto os picos secundários de Cu2(OH)3(NO3) aparecem em valores mais baixos de pH (8 e 11). Os resultados dos espectros de FTIR comprovaram o surgimento de Cu2(OH)3(NO3) através das vibrações relacionadas ao hidróxido de nitrato. Os resultados das imagens do MEV-FEG indicaram as alterações na morfologia obtidas através dos diferentes surfactantes e pH do meio, em que para valores menores, pH = 8, a morfologia apresentou aspecto de folha e, ao aumentá-lo para pH = 13, a morfologia se alterou para um aglomerado de nanopartículas com aspecto de flor. Os resultados de BET indicaram que as amostras obtidas sem a presença de surfactante e com PEG, em pH = 8, exibiram a maior e menor área superficial, sendo essas de 18.935 e 4.531 m2.g-1, respectivamente. Os testes fotocatalíticos indicaram que o aumento da área superficial favorece a atividade fotocatalítica, onde a amostra sem surfactante obtida em pH 8 e a amostra obtida com PVP em pH 11 reduziram 100% a concentração do corante azul de metileno.
One-step synthesis of CaMoO4: Eu3+ nanospheres by ultrasonic spray pyrolysis
(Springer, 2017-08-02) Paskocimas, Carlos Alberto; Almeida, Cláudio Romero Rodrigues de; Lovisa, Laura Ximena; Santiago, Anderson de Azevedo Gomes; Li, Maximo Siu; Silva, Elson Longo da; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
In this paper, CaMoO4 and of Eu3+-doped CaMoO4 nanospheres were prepared by a spray pyrolysis method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectra and photoluminescence spectroscopy. XRD patterns indicate that these crystals have a scheelite-type tetragonal structure. The morphology of the CaMoO4: Eu3+ nanospheres was investigated from the FESEM results and it was observed the formation of spherical particles peculiar to the synthesis method used. Sample of pure CaMoO4 thermally treated 1000 °C exhibit a photoluminescence behavior broadband type with emission in white light according to the calculated values of the CIE coordinates: x=0.37, y=0.37. The emission intensity in the red for samples doped with Eu3+ (5 D0 → 7 F2 in 615 nm) increases directly with the dopant concentration
Optimização da degradação fotocatalítica do levofloxacino através da heteroestrutura de Bi2WO6/CuO
(Universidade Federal do Rio Grande do Norte, 2024-07-31) Wilson, Rebecca Roberta Ysraelle Oliveira Verde; Motta, Fabiana Villela da; Delmonte, Mauricio Roberto Bomio; https://orcid.org/0000-0002-3523-737X; http://lattes.cnpq.br/9918299069511517; http://lattes.cnpq.br/5053372623203630; Bohn, Felipe; Lovisa, Laura Ximena
O descarte inadequado de resíduos farmacêuticos contendo antibióticos contamina sistemas aquáticos, promovendo o aparecimento de superbactérias resistentes. A fotocatálise heterogênea (FH) e as heteroestruturas binárias emergem como estratégias promissoras para degradar esses contaminantes de forma eficiente. Neste estudo, uma estrutura de nanofolhas de CuO foi decorada com nanoflores de Bi2WO6 para formar heteroestruturas n-p de Bi2WO6/CuO através de um processo simples em duas etapas, utilizando uma abordagem hidrotermal assistida por micro-ondas (SHAM). Os fotocatalisadores sintetizados foram avaliados através da degradação do antibiótico levofloxacino como poluente alvo sob irradiação solar. As propriedades ópticas dos fotocatalisadores BWO/CuO foram avaliadas por UV-Vis e FL, enquanto a morfologia estrutural foi analisada por MEV-FEG. Os resultados de DRX e FT-IR corroboram, indicando a cristalinidade e a pureza das amostras obtidas pela SHAM. Os difratogramas de Raios-X mostraram a obtenção de fases cristalinas de β-Bi2WO6 ortorrômbica e β-CuO monoclínica, sem presença de fases secundárias. As imagens de MEV-FEG das heteroestruturas revelaram uma morfologia que se assemelha a uma flor tridimensional com nanofolhas aglomeradas, as quais são derivadas das amostras puras. Análises de BET indicaram que a amostra BW/Cu-10 possui a maior área superficial entre as heteroestruturas, o que explica seu desempenho fotocatalítico superior. A degradação do levofloxacino por BW/Cu-10 atingiu 95% de eficiência em 120 minutos. As capacidades fotocatalíticas aprimoradas das heteroestruturas BWO/CuO foram atribuídas à construção de uma heterojunção n–p, à separação eficaz de cargas de acordo com o mecanismo do tipo n-p e ao tempo de vida prolongado dos portadores, o que suprimiu eficientemente a recombinação de elétrons/buracos fotoinduzidos. As heteroestruturas BWO/CuO obtidas foram estáveis durante quatro ciclos consecutivos com capacidade de degradação quase constante. Portanto, devido às suas promissoras capacidades fotocatalíticas, BWO/CuO são fotocatalisadores adequados para aplicações de tratamento ambiental.
Photoluminescence properties of (Eu, Tb, Tm) co-doped PbMoO4 obtained by sonochemical synthesis
(Elsevier, 2017-04-05) Gurgel, G. M.; Lovisa, Laura Ximena; Pereira, Laurenice Martins; Motta, Fabiana Villela da; Li, Maximo Siu; Silva, Elson Longo da; Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio
The PbMoO4 co-doped with Tm3+, Tb3+ Eu3+ with scheelita structure was synthesized by the sonochemical method. The photoluminescent properties, structural and color coordinates emitted by phosphors were investigated. The structural analysis of the crystal and the changes in lattice parameters confirm that the rare earth ions (RE3+) were successfully introduced into the host of the PbMoO4. The relationship between energy gap (Egap) and the concentration of RE3+ ions was also discussed, the Egap is significantly influenced by the degree of structural order-disorder present in the crystal lattice. The PbMoO4:RE3+ shows light emission in green. Under UV excitation, Photoluminescence (PL) shows a broad band centered at 520 nm and smaller bands belonging to transitions of RE3+: 1G4 → 3 F4 and 1D2 → 3H4 at 480 and 533 nm (Tm3+), 5D4 → 7 Fj (j = 6, 5) at 493 and 550 nm (Tb 3+) 5D0 → 7Fj (j = 1, 2, 4) 593, 615 and 702 nm (Eu3+)
Photoluminescence properties of (Eu, Tb, Tm) co-doped PbMoO4 obtained by sonochemical synthesis
(Elsevier, 2017-04-05) Paskocimas, Carlos Alberto; Lovisa, Laura Ximena; Gurgel, G. M.; Pereira, Laurenice Martins; Motta, Fabiana Villela da; Silva, Elson Longo da; Li, Maximo Siu; Delmonte, Maurício Roberto Bomio
The PbMoO4 co-doped with Tm3+, Tb3+ Eu3+ with scheelita structure was synthesized by the sonochemical method. The photoluminescent properties, structural and color coordinates emitted by phosphors were investigated. The structural analysis of the crystal and the changes in lattice parameters confirm that the rare earth ions (RE3+) were successfully introduced into the host of the PbMoO4. The relationship between energy gap (Egap) and the concentration of RE3+ ions was also discussed, the Egap is significantly influenced by the degree of structural order-disorder present in the crystal lattice. The PbMoO4:RE3+ shows light emission in green. Under UV excitation, Photoluminescence (PL) shows a broad band centered at 520 nm and smaller bands belonging to transitions of RE3+: 1G4 → 3F4 and 1D2 → 3H4 at 480 and 533 nm (Tm3+), 5D4 → 7Fj (j = 6, 5) at 493 and 550 nm (Tb 3+) 5D0 → 7Fj (j = 1, 2, 4) 593, 615 and 702 nm (Eu3+)
Photoluminescent properties of ZrO2: Tm3+, Tb3+, Eu3+ powders — A combined experimental and theoretical study
(Elsevier, 2017-02-25) Paskocimas, Carlos Alberto; Lovisa, Laura Ximena; Andrés, Juan; Gracia, Lourdes; Li, Maximo Siu; Delmonte, Maurício Roberto Bomio; Araújo, Vinícius Dantas; Silva, Elson Longo da; Motta, Fabiana Villela da
Rare-earth (RE) element-based materials for optical applications have received increasing attention owing to the emission properties of RE ions, which render these materials suitable for use in color displays, lasers, and solid-state lighting. In the present work, ZrO2:RE (RE = Tm3+, Tb3+, and Eu3+) powders were obtained via complex polymerization, and characterized by means of X-ray diffraction (XRD), Raman spectroscopy, UV–visible absorption spectroscopy, and photoluminescence measurements. The XRD patterns and Raman spectra revealed the tetragonal phase of ZrO2 co-doped with up to 4 mol.% RE3+ and stabilization of the cubic phase, for up to 8 mol.% RE3+. In addition, the photoluminescence measurements revealed simultaneous emissions in the blue (477 nm), green (496.02 nm and 548.32 nm), and red-orange (597.16 nm and 617.54 nm) regions. These emissions result from the Tm3+, Tb 3+, and Eu3+ ions, respectively. Energy transfers, such as 1G4 levels (Tm3+) → 5D4 (Tb3+) and 5D4 levels (Tb3+) → 5D0 (Eu3+), occurred during the emission process. Calculations based on density functional theory (DFT) were performed, to complement the experimental data. The results revealed that structural order/disorder effects were generated in the cubic and tetragonal ZrO2 phases in the ZrO2:Eu3+ powders, and changes in the electronic structure were manifested as a decrease in the band gap values. The chromaticity coordinates of all the samples were determined from the PL spectrum. The coordinates, x = 0.34 and y = 0.34, of the ZrO2:8%RE sample corresponded to a point located in the white region of the CIE diagram and color correlated temperature (CCT) was found to be 5181 K. More importantly, the present results indicate that ZrO2:RE powders constitute promising photoluminescent materials for use in new lighting devices.
Presence of excited electronic states on terbium incorporation in CaMoO4: Insights from experimental synthesis and first-principles calculations
(Elsevier, 2021-02) Tranquilin, Ricardo Luis; Oliveira, Marisa Carvalho de; Santiago, Anderson de Azevedo Gomes; Lovisa, Laura Ximena; Ribeiro, Renan Augusto Pontes; Silva, Elson Longo da; Lazaro, Sergio R. de; Almeida, Cláudio Romero Rodrigues de; Paskocimas, Carlos Alberto; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio
We present a combined experimental and theoretical study to understand the structure and electronic and optical properties of CaMoO4:xTb3+ (x = 1 mol%, 2 mol%, and 4 mol%) microspheres. The microspheres were prepared by ultrasonic spray pyrolysis and characterized by X-ray diffraction (XRD), field-emission gun scanning electron microscopy (FEG-SEM), micro Raman spectroscopy, and photoluminescence (PL) spectroscopy. First-principles quantum mechanical calculations were performed at the density functional theory level to obtain the geometry and electronic properties of CaMoO4:xTb3+ microspheres in the ground electronic state and excited electronic states (singlet and triplet). These results, combined with XRD patterns, indicate that these crystals have a scheelite-type tetragonal structure. The morphology of the CaMoO4:xTb3+(x = 1 mol%, 2 mol%, and 4 mol%) samples was investigated by FEG-SEM, and a spherical shape was found. The optical properties were investigated by UV–vis spectroscopy and PL spectroscopy, and the chromaticity coordinates of these compounds were obtained. The relationships between the PL properties and the Raman spectra indicate that Tb3+-doped CaMoO4 microspheres constitute promising photoluminescent materials for use in new lighting devices. This also allowed us to understand the charge transfer process that happens in the singlet (s) ground state and the singlet (s*) and triplet (t*) excited states, which generates the photoluminescent emissions of the Tb3+-doped CaMoO4 microspheres
Propriedade fotoluminescente da ZrO2: Tb+3, Eu+3, Tm+3 obtida pelo método de polimerização de complexos
(Universidade Federal do Rio Grande do Norte, 2013-12-16) Lovisa, Laura Ximena; Motta, Fabiana Villela da; ; http://lattes.cnpq.br/9918299069511517; ; http://lattes.cnpq.br/3096918631525114; Macedo, Daniel Araujo de; ; http://lattes.cnpq.br/1027496814443777; Delmonte, Mauricio Roberto Bomio; ; http://lattes.cnpq.br/9558299312183852; Araújo, Vinícius Dantas de; ; http://lattes.cnpq.br/9752753965948564
Estudos recentes investigam uma nova classe de materiais inorgânicos que surgem como uma opção promissora em aplicações de alto desempenho no campo da fotoluminescência. Destaque para fósforos dopados com íons de terras raras (TR +3 ), que possuem uma alta eficiência luminosa, um longo tempo de decaimento e por serem capazes de emitir radiações na faixa do visível, específicas de cada elemento. Neste trabalho, foram sintetizadas nanopartículas de ZrO2:Tb +3 , Eu +3 , Tm +3 pelo método de polimerização dos complexos (MPC). Foram investigadas as influências causadas pela temperatura de tratamento térmico e pelo teor dos dopantes no comportamento fotoluminescente da zircônia. As partículas foram calcinadas nas temperaturas de 400, 500 e 600ºC durante duas horas e a concentração dos dopantes variou em 1, 2, 4 e 8% mol TR +3 . As amostras foram caracterizadas por análises térmicas (TG/ DSC), difração de raios X (DRX), medidas de fotoluminescência (FL) e espectroscopia na região do UV-Visível (UV-vis). Os resultados de difração de raios X confirmaram a formação das fases tetragonal e cúbica de acordo com o teor de dopantes. Os espectros de fotoluminescência apresentam emissões simultâneas correspondentes na região do azul (450 nm), do verde (550 nm) e do vermelho (615 nm). De acordo com os resultados obtidos, as partículas de ZrO2 codopadas com íons de terras raras apresentam-se como um material promissor para emissão no branco com um potencial de aplicação no campo da fotoluminescência
Propriedades fotoluminescentes de nanopartículas de CaWO4 dopadas com Sm3+ e Tb3+ obtidas pelo método sonoquímico
(Universidade Federal do Rio Grande do Norte, 2019) Silva, Joyce Marina Paiva da; Motta, Fabiana Villela da; Delmonte, Maurício Roberto Bomio; Lovisa, Laura Ximena
Os tungstatos vêm sendo objeto de estudo devido as suas diversas aplicações, tais como em lasers, sensores, catalisadores, lâmpadas fluorescentes, entre outras. Entre os tungstatos, o tungstato de cálcio (CaWO4) tem se destacado pelas suas propriedades fotoluminescentes, que podem ser favorecidas pela dopagem com terras raras. Neste trabalho, o método de síntese sonoquímico foi utilizado para a obtenção de nanopartículas de CaWO4 dopado com Sm3+ e Tb3+. As nanopartículas obtidas foram caracterizadas por difração de raios X (DRX), espectroscopia Raman, microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET) e espectroscopia ultravioleta visível (UV-Vis). Para as propriedades fotoluminescentes, foram realizadas medidas em temperatura ambiente e em temperaturas mais baixas para análise de dopagem em cores de emissão. Os resultados de DRX mostram a formação de uma estrutura scheelita sem a presença de segunda fase. As imagens obtidas por MEV e MET indicam a formação de nanoesferas para a amostra pura e dopadas com samário, enquanto que a dopagem com térbio resulta na formação de nanobastões. Os espectros de fotoluminescência a temperatura ambiente da amostra CaWO4 pura apresenta uma emissão azul, enquanto que a dopagem com samário reduz essa intensidade e a dopagem com térbio promove emissão na cor verde. Ao reduzir a temperatura de emissão, os defeitos da matriz são favorecidos, alterando a cor da emissão para a região azul/verde.
Propriedades Fotoluminescentes do ZnMoO4 codopado com íons de terras raras obtidos a partir do método sonoquímico
(2018-02-09) Lovisa, Laura Ximena; Motta, Fabiana Villela da; ; ; Delmonte, Mauricio Roberto Bomio; ; Nascimento, Jose Heriberto Oliveira Do; ; Melo, Maxymme Mendes de; ; Araújo, Vinícius Dantas de;
Uma nova classe de materiais inorgânicos, que surgem como uma opção promissora em aplicações de alto desempenho no campo da fotoluminescência, tem ganhado uma atenção especial. Este grupo é constituído pelos molibdatos, XMoO4 (X: íon metálico), dopados com elementos de terras raras (TR). As características que descrevem estes materiais são: alta eficiência luminosa, longo tempo de decaimento e apresentação de emissões no visível. Neste trabalho foram sintetizadas partículas de ZnMoO4 e a série ZnMoO4: 1% Tm+3 , 1% Tb+3, x Eu+3 (x = 1, 1.5, 2, 2.5 e 3%mola partir do método sonoquímico. Foram investigadas as influências causadas pelo teor dos dopantes e pelo tratamento térmico no comportamento fotoluminescente. Os resultados de difração de raios X confirmaram a formação da fase α- ZnMoO4 com estrutura cristalina triclínica para as partículas. Os valores da energia de gap estão na faixa de 3.58 e 4.22 eV. As imagens do MEV-FEG apresentam uma mudança na morfologia das partículas em conformidade com o aumento da dopagem. A morfologia das partículas foi interpretada com base em uma análise comparativa entre as imagens modeladas teoricamente e as experimentais de microscopia eletrônica de varredura de emissão de campo. Os cálculos de primeiro princípio em um nível de teoria funcional de densidade foram realizados para obter os valores de energias de superfície e estabilidade relativa das superfícies (120), (001), (011), (201) e (100) usando a construção de Wulff. Os resultados de fotoluminescência mostram as emissões específicas do Tb+3 e do Eu+3.Os valores das coordenadas de cromaticidade sofreram bastante influencia com aumento da temperatura de tratamento, exibindo emissão na região do amarelo – laranja, do verde e do branco.
Síntese e caracterização de β-ZnMoO4:xNd3+ obtidos pelo método hidrotérmico convencional
(Universidade Federal do Rio Grande do Norte, 2022-02-15) Nicácio, Tanara Caroline Nunes; Motta, Fabiana Villela da; https://orcid.org/0000-0002-3523-737X; http://lattes.cnpq.br/9918299069511517; 0000-0002-0647-0447; http://lattes.cnpq.br/6775126787399065; Santiago, Anderson de Azevedo Gomes; https://orcid.org/0000-0002-9173-0476; http://lattes.cnpq.br/6982375962705773; Lovisa, Laura Ximena; https://orcid.org/0000-0003-4505-7177; http://lattes.cnpq.br/3096918631525114
Os materiais cerâmicos avançados são investigados intensivamente para aplicações em diversos setores industriais; dentre esses materiais, pode-se citar os óxidos ternários. Os molibdatos fazem parte desta classe de cerâmicas avançadas, com fórmula química MMoOx (M = Zn, Ca, Mg, Sr), têm grande importância devido suas várias aplicações como fotocatalisadores, eletrodos, materiais luminescentes e detectores de cintilação. O molibdato de zinco tem atraído significativa atenção por ser atóxico e exibir excelente desempenho óptico e elétrico. Especificamente, as propriedades fotoluminescentes e fotocatalíticas são potencializadas pela adição de elementos de terras raras (TR) na matriz de ZnMoO4. Nesse sentido, o presente trabalho relata e compara a atividade fotocatalítica do ZnMoO4 dopado com diferentes porcentagens de neodímio (Zn1- xMoO4:xNd3+ com x = 0, 0,11, 0,22 e 0,33 mol %) para remoção do corante azul de metileno da água. Os catalisadores foram sintetizados por síntese hidrotérmica convencional na temperatura de 140ºC por 8 horas. As propriedades ópticas também foram investigadas a fim de relacionar com a propriedades fotocatalíticas. O método hidrotérmico empregado neste trabalho mostrou-se eficiente para a obtenção das partículas de ZnMoO4. Os padrões de DRX juntamente com o refinamento estrutural, mostraram a formação da fase β-ZnMoO4 para todas as amostras, que corresponde a estrutura cristalina monoclínica do tipo wolframita. Não houve formação de fase secundária, indicando que a dopagem ocorreu com sucesso. As micrografias do MEV-FEG demonstraram uma evolução da morfologia das partículas em conformidade com o aumento da quantidade do dopante (Nd3+), tendo formatos irregulares do tipo placa. A energia de gap dos Zn1-xMoO4:xNd3+ variou entre 3,18 eV à 3,14 eV. Os resultados de fotoluminescência demonstraram que a amostra β-ZnMoO4:xNd3+ com X = 0,33 apresentou a maior intensidade fotoluminescente. Quanto à atividade fotocatalítica após o reuso em três ciclos, o catalisador mostrou-se eficiente, chegando a 98,8% de degradação do corante, tornando o processo de fotodegradação muito favorável para aplicação em águas residuais.
Structure, morphology and photoluminescence emissions of ZnMoO4: RE 3+=Tb3+ - Tm3+ - X Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles obtained by the sonochemical method
(Elsevier, 2018-06-25) Paskocimas, Carlos Alberto; Lovisa, Laura Ximena; Oliveira, Marisa Carvalho de; Andres, Juan; Gracia, Lourdes; Li, Maximo Siu; Silva, Elson Longo da; Tranquilin, Ricardo Luis; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
ZnMoO4 and ZnMoO4: RE3+ = 1% Tb3+, 1% Tm3+, x Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles were prepared by a sonochemical method. The influence of the dopant content on photoluminescent behavior was investigated. The X-ray diffraction results confirmed the formation of the α-ZnMoO4 phase with a triclinic crystalline structure. The influence of the chemical compositions on photoluminescence emissions has been studied and the results clearly show the specific emissions of Tb3+ and Eu3+, simultaneously, with a strong contribution of the matrix. Band gap values are in the range of 3.55–4.25 eV. From the values calculated for the CIE coordinates, it was observed that this material develops an emission tendency in the orange-red region. It has been demonstrated for the first time that the sample ZnMoO4: 1% Tb3+, 1% Tm3+, 2% molEu3+, presented higher photoluminescence intensity. At higher concentrations of RE3+, the quenching effect was observed. The morphology of samples are interpreted based on a comparative analysis of the calculated and experimental field emission scanning electron microscopy (FE-SEM) images. First-principle calculations at a density functional theory level were performed to obtain the values of surface energies and relative stability of the (120), (001), (011), (201), and (100) surfaces by employing the Wulff construction. A complete map of the available morphologies of ZnMoO4 and ZnMoO4:12.5%molEu3+ is obtained and a possible explanation for the transformation processes is provided in which the experimental and theoretical morphologies can match. The present study offers a fundamental knowledge that is expected to enable the fabrication of ZnMoO4-based phosphor materials with a controllable emission peak shift and intensity
Structure, morphology and photoluminescence emissions of ZnMoO4: RE 3+=Tb3+ -Tm3+ - x Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles obtained by the sonochemical method
(Elsevier, 2018-06-25) Lovisa, Laura Ximena; Oliveira, Marisa Carvalho de; Andrés, Juan; Gracia, Lourdes; Li, Maximo Siu; Silva, Elson Longo da; Tranquilin, Ricardo Luis; Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
ZnMoO4 and ZnMoO4: RE3+= 1% Tb3+, 1% Tm3+, x Eu3+ (x = 1, 1.5, 2, 2.5 and 3 mol%) particles were prepared by a sonochemical method. The influence of the dopant content on photoluminescent behavior was investigated. The X-ray diffraction results confirmed the formation of the α-ZnMoO4 phase with a triclinic crystalline structure. The influence of the chemical compositions on photoluminescence emissions has been studied and the results clearly show the specific emissions of Tb3+ and Eu3+, simultaneously, with a strong contribution of the matrix. Band gap values are in the range of 3.55 to 4.25 eV. From the values calculated for the CIE coordinates, it was observed that this material develops an emission tendency in the orange-red region. It has been demonstrated for the first time that the sample ZnMoO4: 1% Tb3+, 1% Tm3+, 2% molEu3+, presented higher photoluminescence intensity. At higher concentrations of RE3+, the quenching effect was observed. The morphology of samples are interpreted based on a comparative analysis of the calculated and experimental field emission scanning electron microscopy (FE-SEM) images. First-principle calculations at a density functional theory level were performed to obtain the values of surface energies and relative stability of the (120), (001), (011), (201), and (100) surfaces by employing the Wulff construction.A complete map of the available morphologies of ZnMoO4 and ZnMoO4:12.5%molEu3+ is obtained and a possible explanation for the transformation processes is provided in which the experimental and theoretical morphologies can match. The present study offers a fundamental knowledge that is expected to enable the fabrication of ZnMoO4-based phosphor materials with a controllable emission peak shift and intensity
Tb3+/Pr3+ co-doped ZnMoO4 phosphor with tunable photoluminescence and energy transfer processes
(Elsevier, 2019-10) Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio; Lovisa, Laura Ximena; Fernandes, Y.L.R.L.; Garcia, Laurênia Martins Pereira; Barros, Bráulio S.; Silva, Elson Longo da; Motta, Fabiana Villela da
ZnMoO4:Tb3+, Pr3+ particles in different Tb:Pr ratios (2:0, 1.5:0.5, 1:1, 0.5:1.5 and 0:2) were synthesized by the sonochemical method. These materials were characterized structurally, morphologically and optically by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Ultraviolet–visible absorption spectroscopy and Photoluminescence (PL). From studying the photoluminescent properties, the PL spectra presented 5 D4 → 7 Fj (j = 6, 5, 4 and 3) transitions bands of Tb3+, along with the transitions 3 P0 → 3 H5, 1 D2 → 3 H4, 3 P0 → 3 H6 and 3 P0 → 3 F3 of Pr3+. Time resolved photoluminescence was investigated and an energy transfer (n) mechanism between the matrix and the Tb3+ and Pr3+ ions is simultaneously proposed for better understanding the process efficiency. Parallel to this perspective, the photocatalytic behavior of ZnMoO4:Tb3+, Pr3+ was evaluated. The degradation of methylene blue dye was favored by the effect of increasing the Pr3+concentration. This work deals with the development of inorganic phosphor materials capable of converting UV radiation into light-emitting diode, which can be suitably combined to produce white light

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