VINICIUS RIBAS DE MORAIS

VINICIUS RIBAS DE MORAIS

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Preparation of Dy3+-doped calcium magnesium silicate phosphors by a new synthesis method and its luminescence characterization
2018 - MORAIS, VINICIUS R. de; LEME, DANIEL de R.; YAMAGATA, CHIEKO
Recently, rare-earth doped alkaline earth silicates have been researched extensively as a new generation of afterglow phosphors. Compared with the conventional sulphide materials used for this purpose, silicates yield luminescence with longer duration time and higher bright, as well as improved chemical stability and lower cost. In the present work, Dy-doped calcium magnesium silicate phosphors were prepared by joining the methods sol-gel and co precipitation. Silica gel was obtained from sodium silicate solution. Ca, Mg and Dy hydroxides, precipitated from chloride solutions with NaOH, were added to the obtained gel. After washing for removal of Cl- ions, the product was annealed at 1000°C for 2 hours. XRD results confirmed the formation of diopside phase (CaMgSi2O6). The product was later characterized by SEM and luminescence spectroscopy.
Synthesis and characterization of bioactive ceramic in CaO-MgO-SiO2 system
2018 - LEME, D.R.; MORAIS, V.R.; RODAS, A.C.D.; HIGA, O.Z.; YAMAGATA, C.
Na2SiO3 solution and chloride solutions of calcium and magnesium were used as raw materials. HCl was added to Na2SiO3 solution resulting in gel of silica. In order to obtain a mixture of Si gel, Ca2+ and Mg2+, calcium and magnesium solutions were blended into the gel. After adding NaOH to the mixture, Ca2+ and Mg2+ ions precipitated as hydroxides. Subsequently, it was dried to attain the ceramic precursor powder, which was calcined at 900 ºC for 1h, compacted into a pellet form and sintered at 1200 ºC for 2h. The ceramic body was characterized by SEM, XRD and FTIR. In vitro test for bioactivity verification was performed in SBF. A surface deposition of hydroxyapatite on the ceramic body was observed after 3 days. The cytotoxicity test revealed that the material has cell viability above 70%, meaning that it is not toxic for the cells, according to ISO 10993-5 standard.
Novel method for the synthesis of Dy-doped yttrium disilicate phosphoros
2018 - MORAIS, V.R.; REZENDE, D.L.; YAMAGATA, C.
The complex high temperature polymorphism (Y, α, β, γ and δ structures) of yttrium disilicate (Y2Si2O7) naturally lead to relatively broad emission, originating from ions placed in different symmetry sites, for example, the replacing of Y3+ by rare earth ions. Y2Si2O7 as the host lattice shows a high thermal and chemical stability compared with other well-studied phosphors such as ZnS and CdS. When doped with different metallic ions, yttrium silicates exhibit attractive luminescent properties for potential applications, such as plasma displays, laser materials and high-energy phosphors. The sol-gel technique provides an available method to prepare ceramic powders, with higher purity and homogeneity compared to the conventional solid-state reaction of mixed oxides. In the present work, a novel sol-gel and co-precipitation combined method has been proposed for synthesis of RE3+ doped Y2Si2O7 (RE=Dy). Silica nanoparticles were obtained by surfactant-assisted sol-gel process, using sodium silicate (Na2SiO3) as precursor, and then Y3+ and Dy3+ ions were precipitated over these particles. The RE3+:Y2Si2O7 obtained product was analyzed by SEM, XRD and luminescence spectroscopy. Crystalline Y2Si2O7 was obtained at lower temperatures compared with traditional methods. The α-phase was obtained at 1100 and 1200°C, and β-phase at 1300°C. Comparing photoluminescence spectra of α and β-phases, the later showed higher intensity luminescence peaks.
Síntese de silicato de lantânio tipo apatita pelo método sol-gel utilizando silicato de sódio como fonte de sílica
2016 - SILVA, F.S.; RODRIGUES, V.G.; MISSO, A.M.; MORAIS, V.R.; YAMAGATA, C.
Ceramics of lanthanum silicate apatite-type have been studied with great technological interest at IT-SOFC applications (Intermediate Temperature Solid Oxide Fuel Cell) for having good ionic conductivity at intermediate temperatures (600-800°C), higher than that of YSZ (Ytria Stabilized Zirconia) in high-temperature SOFCs. At this work has made the synthesis of the lanthanum silicate apatite-type from Na2SiO3 as a source of silica by the modified sol-gel method that allowed the formation of ceramic powders of lanthanum silicate apatite-type in calcination temperature at 900°C, which is much lower than those other methods of synthesis. Analysis by x-ray diffraction (XRD) showed the lanthanum silicate apatite-type phase as the main phase. Scanning electron microscopy was used to nanometric powders observation.