J. Sczancoski - Academia.edu (original) (raw)
Papers by J. Sczancoski
Journal of Materials Science, 2015
Inorganic Chemistry, 2014
Neodymium calcium titanate, (Ca 0.99 Nd 0.01 )TiO 3 powders were synthesized by the complex polym... more Neodymium calcium titanate, (Ca 0.99 Nd 0.01 )TiO 3 powders were synthesized by the complex polymerization method and heat treated at different temperatures for 2 h under air atmosphere. The structural evolution of these powders as a function of heat treatment temperature was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were investigated by Ultraviolet-visible (UV-vis) absorption spectroscopy and Photoluminescence (PL) measurements. XRD patterns, Rietveld refinement and MR spectra indicated that the powders heated treated at 750 • C for 2 h present an orthorhombic structure without secondary phases. UV-vis measurements suggested the presence of intermediary energy in disordered (Ca 0.99 Nd 0.01 )TiO 3 powders. Broad and narrow bands were observed in the PL spectra of these powders when excited with 350 nm wavelength. The broad bands were associated to the structural defects and/or p-d electronic transitions while, the narrow bands were ascribed to f-f transitions arising from Nd 3+ ions.
Physica B-Condensed Matter, 2009
BaðZr 0:25 Ti 0:75 ÞO 3 (BZT) powders were synthesized by the polymeric precursor method (PPM) at... more BaðZr 0:25 Ti 0:75 ÞO 3 (BZT) powders were synthesized by the polymeric precursor method (PPM) at different temperatures (400, 500 and 700 1C) for 2 h and by the solid state reaction (SSR) at 1350 1C for 4 h. These powders were analyzed by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns indicated that the crystalline BZT powders prepared by both methods present a cubic structure. The different optical band gap values were observed from the UV-vis spectra, suggesting the presence of intermediary energy levels (shallow and deep holes) within the band gap. When excited with 350 nm wavelength at room temperature, the BZT powders obtained by SSR exhibited only one broad PL band with a maximum at around 467 nm (blue emission). On the other hand, it was noted the presence of two broad bands when BZT powders were prepared by the PPM, where the correspondent positions are influenced by the heat treatment temperatures. Finally, a model was proposed in order to explain the origin of the PL property in these powders.
Journal of Nanomaterials, 2012
Photoluminescence (PL) is an optical phenomenon exhibited by some semiconductor materials when ex... more Photoluminescence (PL) is an optical phenomenon exhibited by some semiconductor materials when excited by an electromagnetic radiation source. After the excitation and recombination processes, these kinds of materials are able to emit photons with less energy than those employed during the electronic excitation. Initially, the researches on the PL properties focused on crystalline materials under cryogenic conditions. However, from the technological viewpoint, the discovery of new materials with visible PL emissions at room temperature has become more interesting for the improvement or development of electrooptic devices. Currently, functional and practical applications of this physical phenomenon in our daily life can be found in light-emitting diodes, lasers, lamps, sensors, scintillators, electronic displays, and so on. In this special issue, the reader will find 10 selected papers briefly summarized below.
The Journal of Physical Chemistry C, 2009
PbMoO 4 micro-octahedrons were prepared by the coprecipitation method at room temperature without... more PbMoO 4 micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120°C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra confirmed that the PbMoO 4 micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnected along a common crystallographic orientation (oriented-attachment), resulting in self-organized structures. An intense blue PL emission at room temperature was observed in these micro-octahedrons when they were excited with a 350 nm wavelength. The origin of the PL emissions as well as its intensity variations are explained by means of a model based on both distorted [MoO 4 ] and [PbO 8 ] clusters into the lattice. *
Solid State Sciences, 2007
Strontium zirconate (SrZrO 3 ) powders have been synthesized by the polymeric precursor method af... more Strontium zirconate (SrZrO 3 ) powders have been synthesized by the polymeric precursor method after heat treatment at different temperatures for 2 h in oxygen atmosphere. The decomposition of precursor powder was followed by thermogravimetric analysis, X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman). The UVevis absorption spectroscopy measurements suggested the presence of intermediary energy levels in the band gap of structurally disordered powders. XRD, Rietveld refinement and FT-Raman revealed that the powders are free of secondary phases and crystallizes in the orthorhombic structure.
Solid State Sciences, 2008
Calcium titanate, CaTiO 3 powders were prepared by the polymeric precursor method and annealed at... more Calcium titanate, CaTiO 3 powders were prepared by the polymeric precursor method and annealed at different temperatures for 2 h in a conventional furnace and for 30 min on an adapted microwave oven. The effect of microwave energy on structural and photoluminescent behavior of CaTiO 3 powders was investigated by means of X-ray diffraction, micro-Raman scattering and photoluminescence measurements. The results of the CaTiO 3 powders processed in the microwave oven showed a high structural organization compared to conventional treatment.
O3 powders](https://attachments.academia-assets.com/53713404/thumbnails/1.jpg)
](Solid State Sciences, 2010
[Ba 1ex Y 2x/3 ](Zr 0.25 Ti 0.75 )O 3 powders with different yttrium concentrations (x ¼ 0, 0.025... more [Ba 1ex Y 2x/3 ](Zr 0.25 Ti 0.75 )O 3 powders with different yttrium concentrations (x ¼ 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultravioletevisible (UVevis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO 6 ] clusters is able to change the interaction forces between the OeTieO and OeZreO bonds. XANES spectra were used to obtain information on the offcenter Ti displacements or distortion effects on the [TiO 6 ] clusters. The different optical band gap values estimated from UVevis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region.
Optics Communications, 2008
Intense violet-blue photoluminescence (PL) emission at room temperature was verified in BaZrO 3 (... more Intense violet-blue photoluminescence (PL) emission at room temperature was verified in BaZrO 3 (BZO) powders with structural order-disorder. Ab-initio calculations, ultraviolet-visible absorption spectroscopy and PL were performed. Theoretical results showed that the local disorder in the network-formed Zr clusters present an important role in the formation of hole-electron pair. The experimental data and theoretical results are in agreement, indicating that the PL emission in BZO powders can be related to the structural order-disorder degree in the lattice.
Optical Materials, 2009
a b s t r a c t (Sr 0.995 Tm 0.005 )ZrO 3 (STZO) powders were prepared by the polymeric precursor... more a b s t r a c t (Sr 0.995 Tm 0.005 )ZrO 3 (STZO) powders were prepared by the polymeric precursor method and heat treated at different temperatures for 2 h under oxygen flow. These powders were analyzed by X-ray diffraction (XRD), Ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) measurements, field-emission gun-scanning electron microscopy (FEG-SEM) and energy dispersive X-ray spectrometry (EDXS). XRD patterns revealed that the powders crystallize in an orthorhombic structure without the presence of secondary phases. UV-vis absorption spectra suggest that the STZO powders heat treated at low temperatures present intermediary energy levels within the band gap as consequence of structural defects in the lattice. PL measurements indicated the presence of broad, broad/narrow and narrow bands in STZO powders. The broad bands were associated to the asymmetric STZO structure and/or p-d transitions while, the narrow bands were ascribed to f-f transitions arising from thulium ions. A simple model was proposed in order to explain the PL behavior of these powders. FEG-SEM micrographs showed that these powders are composed by several microparticles with irregular morphologies and agglomerated nature. EDXS data were used for analyses of chemical compositional of powders.
Materials Science and Engineering: B, 2008
The present paper describes the synthesis, characterization, structural refinement and optical ab... more The present paper describes the synthesis, characterization, structural refinement and optical absorption behavior of lead tungstate (PbWO 4 ) powders obtained by the complex polymerization method heat treated at different temperatures for 2 h in air atmosphere. PbWO 4 powders were characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) spectroscopy and ultraviolet-visible (UV-vis) absorption spectroscopy measurements. XRD, Rietveld refinement and FT-Raman revealed that PbWO 4 powders are free of secondary phases and crystallizes in a tetragonal structure. The UV-vis absorption spectroscopy measurements suggest the presence of intermediary energy levels into the band gap of structurally disordered powders.
Materials Chemistry and Physics, 2009
MgTiO 3 powders were prepared by the complex polymerization method and heat treated at different ... more MgTiO 3 powders were prepared by the complex polymerization method and heat treated at different temperatures for 2 h. These powders were analyzed by X-ray diffraction (XRD), Rietveld refinements, micro-Raman (MR) spectroscopy, X-ray absorption near edge spectroscopy (XANES), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra showed that the crystalline powders have a rhombohedral structure. XANES spectra indicated that the local structure of crystalline MgTiO 3 powders is composed only by [TiO 6 ] clusters, while the disordered exhibit the simultaneous presence of both [TiO 5 ] and [TiO 6 ] complex clusters into the lattice. UV-vis spectra revealed different optical band gap values as a function of heat treatment temperature. This result can be an indicative of intermediary energy levels within the band gap of this material because of structural defects into the perovskite-type structure. PL behavior was attributed to the structural order-disorder and/or distortions on the [TiO 6 ]-[TiO 6 ] complex clusters.
![Research paper thumbnail of Microstructure, dielectric properties and optical band gap control on the photoluminescence behavior of Ba[Zr0.25Ti0.75]O3 thin films](https://attachments.academia-assets.com/53713385/thumbnails/1.jpg)
](Journal of Sol-Gel Science and Technology, 2009
Ba[Zr 0.25 Ti 0.75 ]O 3 (BZT) thin films were synthesized by the complex polymerization method an... more Ba[Zr 0.25 Ti 0.75 ]O 3 (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400°C for different times and at 700°C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultravioletvisible (UV-vis) absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT thin films heat treated at 700°C were approximately 148 and 0.08 at 1 MHz, respectively. UV-vis absorption spectra suggested the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was explained through the optical band gap values associated to the visible light emission components.
Journal of Physics D: Applied Physics, 2009
In this work, Ba(Zr 0.25 Ti 0.75 )O 3 ceramic was prepared by solid-state reaction. This material... more In this work, Ba(Zr 0.25 Ti 0.75 )O 3 ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie-Weiss law. The optical properties were analysed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV-vis spectrum indicated that the Ba(Zr 0.25 Ti 0.75 )O 3 ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO 6 ] distorted clusters into a globally cubic matrix.
![Research paper thumbnail of Intense and broad photoluminescence at room temperature in structurally disordered Ba[Zr0.25Ti0.75]O3 powders: An experimental/theoretical correlation](https://attachments.academia-assets.com/53713387/thumbnails/1.jpg)
](Journal of Physics and Chemistry of Solids, 2008
Intense and broad photoluminescence (PL) emission at room temperature was observed on structurall... more Intense and broad photoluminescence (PL) emission at room temperature was observed on structurally disordered Ba[Zr 0.25 Ti 0.75 ]O 3 (BZT) powders synthesized by the polymeric precursor method. BZT powders were annealed at 573 K for different times and at 973 K for 2 h in oxygen atmosphere. The single-phase cubic perovskite structure of the powder annealed at 973 K for 2 h was identified by X-ray diffraction and Fourier transform Raman techniques. PL emission increased with the increase of annealing time, which reached its maximum value in the powder annealed at 573 K for 192 h. First principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered models. The theoretical calculations and experimental measurements of Ultraviolet-visible absorption spectroscopy indicate that the presence of intermediary energy levels in the band gap is favorable for the intense and broad PL emission at room temperature in disordered BZT powders. The PL behavior is probably due the existence of a charge gradient on the disordered structure, denoted by means of a charge transfer process from [TiO 5 ]-[ZrO 6 ] or [TiO 6 ]-[ZrO 5 ] clusters to [TiO 6 ]-[ZrO 6 ] clusters. r
Journal of Materials Science, 2014
Rare earth samarium (Sm)-doped barium zirconate titanate (Ba 1-x Sm 2x/3 )(Zr 0.3 Ti 0.7 )O 3 (x ... more Rare earth samarium (Sm)-doped barium zirconate titanate (Ba 1-x Sm 2x/3 )(Zr 0.3 Ti 0.7 )O 3 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed singlephase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M-O bonds. Raman spectroscopic study revealed that the substitution of Ba 2? ions by Sm 3? ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm 3? ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel-Fulcher relation.
Journal of Colloid and Interface Science, 2009
SrWO 4 powders were synthesized by the co-precipitation method and processed in a microwavehydrot... more SrWO 4 powders were synthesized by the co-precipitation method and processed in a microwavehydrothermal (MH) at 140 • C for different times. The obtained powders were analyzed by X-ray diffraction (XRD), micro-Raman (MR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra showed that the SrWO 4 powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a high absorption band situated at 831.57 cm −1 , which was ascribed to the W-O antisymmetric stretching vibrations into the [WO 4 ] tetrahedron groups. FEG-SEM micrographs suggested that the processing time is able to influence in the growth process and morphology of SrWO 4 powders. UV-vis absorption spectra revealed different optical band gap values for these powders. A green PL emission at room temperature was verified in SrWO 4 powders when excited with 488 nm wavelength.
Journal of Alloys and Compounds, 2009
Bismuth titanate, Bi 4 Ti 3 O 12 (BiT) powders were synthesized by the complex polymerization met... more Bismuth titanate, Bi 4 Ti 3 O 12 (BiT) powders were synthesized by the complex polymerization method. The structural evolution as a function of heat treatment temperature of these powders was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were verified by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra revealed that the BiT powders heat treated at 700 • C for 2 h under oxygen flow crystallize in an orthorhombic structure without deleterious phases. UV-vis spectra indicated the presence of intermediary energy levels within the band gap of the powders heat treated at low temperatures. The maximum PL emissions of these materials were verified at around 598 nm, when excited by 488 nm wavelengths. Also, it was observed the presence of two broad PL bands, which were attributed to the intermediary energy levels arising from ␣-Bi 2 O 3 and BiT phases. 18] observed a tetragonal structure for this material below 600 • C and an orthorhombic structure at 750 • C. In the last years, different synthesis methods have been reported in the literature for the obtention of BiT powders, mainly including: solid-state reaction , high-energy ball milling process , self-propagating high-temperature , molten salts [24] and flash creation . In contrast, these methods present some drawbacks, such as: formation of secondary phases, contamination by impurities, high heat treatment temperatures, long processing times and nonuniform particle size distribution. A possible alternative for reduction of these problems can be the use of wet chemical methods, such as: sol-gel , citrate gel [29], urea precipitation [30], oxalate coprecipitation [31-33], hydrothermal [34-36], metalorganic decomposition [37] and polymeric precursor [38], hydrolysis . Moreover, these synthesis methods are able to improve the dielectrical, structural, morphological and mechanical properties of BiT oxides .
Journal of Alloys and Compounds, 2009
Intense blue and green photoluminescence (PL) emissions were observed at room temperature in bari... more Intense blue and green photoluminescence (PL) emissions were observed at room temperature in barium zirconate (BaZrO 3 ) powders prepared by chemical method. The powders were analyzed by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption spectroscopy (EXAFS) and ultraviolet-visible (UV-vis) absorption spectroscopy. The XRD patterns indicated the presence of a secondary phase of BaCO 3 in BaZrO 3 powders heat treated at 773 K. K-edge XANES data revealed that Zr atoms presents in at least two Zr environments. EXAFS investigations showed strong bond length dispersion in the first coordination shell around Zr atoms. EXAFS analysis indicated that Zr atoms are coordinated by 6 oxygen in BaZrO 3 powders heat treated at 973 K. UV-vis measurements suggested the presence of intermediary energy levels into the band gap of BaZrO 3 powders heat treated at 773 K. The intense PL emission in BaZrO 3 powders can be attributed to the two Zr environments or ZrO 5 -ZrO 6 clusters.
Journal of Materials Science, 2015
Inorganic Chemistry, 2014
Neodymium calcium titanate, (Ca 0.99 Nd 0.01 )TiO 3 powders were synthesized by the complex polym... more Neodymium calcium titanate, (Ca 0.99 Nd 0.01 )TiO 3 powders were synthesized by the complex polymerization method and heat treated at different temperatures for 2 h under air atmosphere. The structural evolution of these powders as a function of heat treatment temperature was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were investigated by Ultraviolet-visible (UV-vis) absorption spectroscopy and Photoluminescence (PL) measurements. XRD patterns, Rietveld refinement and MR spectra indicated that the powders heated treated at 750 • C for 2 h present an orthorhombic structure without secondary phases. UV-vis measurements suggested the presence of intermediary energy in disordered (Ca 0.99 Nd 0.01 )TiO 3 powders. Broad and narrow bands were observed in the PL spectra of these powders when excited with 350 nm wavelength. The broad bands were associated to the structural defects and/or p-d electronic transitions while, the narrow bands were ascribed to f-f transitions arising from Nd 3+ ions.
Physica B-Condensed Matter, 2009
BaðZr 0:25 Ti 0:75 ÞO 3 (BZT) powders were synthesized by the polymeric precursor method (PPM) at... more BaðZr 0:25 Ti 0:75 ÞO 3 (BZT) powders were synthesized by the polymeric precursor method (PPM) at different temperatures (400, 500 and 700 1C) for 2 h and by the solid state reaction (SSR) at 1350 1C for 4 h. These powders were analyzed by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns indicated that the crystalline BZT powders prepared by both methods present a cubic structure. The different optical band gap values were observed from the UV-vis spectra, suggesting the presence of intermediary energy levels (shallow and deep holes) within the band gap. When excited with 350 nm wavelength at room temperature, the BZT powders obtained by SSR exhibited only one broad PL band with a maximum at around 467 nm (blue emission). On the other hand, it was noted the presence of two broad bands when BZT powders were prepared by the PPM, where the correspondent positions are influenced by the heat treatment temperatures. Finally, a model was proposed in order to explain the origin of the PL property in these powders.
Journal of Nanomaterials, 2012
Photoluminescence (PL) is an optical phenomenon exhibited by some semiconductor materials when ex... more Photoluminescence (PL) is an optical phenomenon exhibited by some semiconductor materials when excited by an electromagnetic radiation source. After the excitation and recombination processes, these kinds of materials are able to emit photons with less energy than those employed during the electronic excitation. Initially, the researches on the PL properties focused on crystalline materials under cryogenic conditions. However, from the technological viewpoint, the discovery of new materials with visible PL emissions at room temperature has become more interesting for the improvement or development of electrooptic devices. Currently, functional and practical applications of this physical phenomenon in our daily life can be found in light-emitting diodes, lasers, lamps, sensors, scintillators, electronic displays, and so on. In this special issue, the reader will find 10 selected papers briefly summarized below.
The Journal of Physical Chemistry C, 2009
PbMoO 4 micro-octahedrons were prepared by the coprecipitation method at room temperature without... more PbMoO 4 micro-octahedrons were prepared by the coprecipitation method at room temperature without the presence of surfactants and processed in a conventional hydrothermal at different temperatures (from 60 to 120°C) for 10 min. These micro-octahedrons were structurally characterized by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy, and its morphology was investigated by field-emission gun scanning electron microscopy (FEG-SEM). The optical properties were analyzed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra confirmed that the PbMoO 4 micro-octahedrons are characterized by a scheelite-type tetragonal structure. FEG-SEM micrographs points out that these structures present a polydisperse particle size distribution in consequence of a predominant growth mechanism via aggregation of particles. In addition, it was observed that the hydrothermal conditions favored a spontaneous formation of micro-octahedrons interconnected along a common crystallographic orientation (oriented-attachment), resulting in self-organized structures. An intense blue PL emission at room temperature was observed in these micro-octahedrons when they were excited with a 350 nm wavelength. The origin of the PL emissions as well as its intensity variations are explained by means of a model based on both distorted [MoO 4 ] and [PbO 8 ] clusters into the lattice. *
Solid State Sciences, 2007
Strontium zirconate (SrZrO 3 ) powders have been synthesized by the polymeric precursor method af... more Strontium zirconate (SrZrO 3 ) powders have been synthesized by the polymeric precursor method after heat treatment at different temperatures for 2 h in oxygen atmosphere. The decomposition of precursor powder was followed by thermogravimetric analysis, X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman). The UVevis absorption spectroscopy measurements suggested the presence of intermediary energy levels in the band gap of structurally disordered powders. XRD, Rietveld refinement and FT-Raman revealed that the powders are free of secondary phases and crystallizes in the orthorhombic structure.
Solid State Sciences, 2008
Calcium titanate, CaTiO 3 powders were prepared by the polymeric precursor method and annealed at... more Calcium titanate, CaTiO 3 powders were prepared by the polymeric precursor method and annealed at different temperatures for 2 h in a conventional furnace and for 30 min on an adapted microwave oven. The effect of microwave energy on structural and photoluminescent behavior of CaTiO 3 powders was investigated by means of X-ray diffraction, micro-Raman scattering and photoluminescence measurements. The results of the CaTiO 3 powders processed in the microwave oven showed a high structural organization compared to conventional treatment.
Solid State Sciences, 2010
[Ba 1ex Y 2x/3 ](Zr 0.25 Ti 0.75 )O 3 powders with different yttrium concentrations (x ¼ 0, 0.025... more [Ba 1ex Y 2x/3 ](Zr 0.25 Ti 0.75 )O 3 powders with different yttrium concentrations (x ¼ 0, 0.025 and 0.05) were prepared by solid state reaction. These powders were analyzed by X-ray diffraction (XRD), Fourier transform Raman scattering (FT-RS), Fourier transform infrared (FT-IR) and X-ray absorption near-edge (XANES) spectroscopies. The optical properties were investigated by means of ultravioletevisible (UVevis) absorption spectroscopy and photoluminescence (PL) measurements. Even with the addition of yttrium, the XRD patterns revealed that all powders crystallize in a perovskite-type cubic structure. FT-RS and FT-IR spectra indicated that the presence of [YO 6 ] clusters is able to change the interaction forces between the OeTieO and OeZreO bonds. XANES spectra were used to obtain information on the offcenter Ti displacements or distortion effects on the [TiO 6 ] clusters. The different optical band gap values estimated from UVevis spectra suggested the existence of intermediary energy levels (shallow or deep holes) within the band gap. The PL measurements carried out with a 350 nm wavelength at room temperature showed that all powders present typical broad band emissions in the blue region.
Optics Communications, 2008
Intense violet-blue photoluminescence (PL) emission at room temperature was verified in BaZrO 3 (... more Intense violet-blue photoluminescence (PL) emission at room temperature was verified in BaZrO 3 (BZO) powders with structural order-disorder. Ab-initio calculations, ultraviolet-visible absorption spectroscopy and PL were performed. Theoretical results showed that the local disorder in the network-formed Zr clusters present an important role in the formation of hole-electron pair. The experimental data and theoretical results are in agreement, indicating that the PL emission in BZO powders can be related to the structural order-disorder degree in the lattice.
Optical Materials, 2009
a b s t r a c t (Sr 0.995 Tm 0.005 )ZrO 3 (STZO) powders were prepared by the polymeric precursor... more a b s t r a c t (Sr 0.995 Tm 0.005 )ZrO 3 (STZO) powders were prepared by the polymeric precursor method and heat treated at different temperatures for 2 h under oxygen flow. These powders were analyzed by X-ray diffraction (XRD), Ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) measurements, field-emission gun-scanning electron microscopy (FEG-SEM) and energy dispersive X-ray spectrometry (EDXS). XRD patterns revealed that the powders crystallize in an orthorhombic structure without the presence of secondary phases. UV-vis absorption spectra suggest that the STZO powders heat treated at low temperatures present intermediary energy levels within the band gap as consequence of structural defects in the lattice. PL measurements indicated the presence of broad, broad/narrow and narrow bands in STZO powders. The broad bands were associated to the asymmetric STZO structure and/or p-d transitions while, the narrow bands were ascribed to f-f transitions arising from thulium ions. A simple model was proposed in order to explain the PL behavior of these powders. FEG-SEM micrographs showed that these powders are composed by several microparticles with irregular morphologies and agglomerated nature. EDXS data were used for analyses of chemical compositional of powders.
Materials Science and Engineering: B, 2008
The present paper describes the synthesis, characterization, structural refinement and optical ab... more The present paper describes the synthesis, characterization, structural refinement and optical absorption behavior of lead tungstate (PbWO 4 ) powders obtained by the complex polymerization method heat treated at different temperatures for 2 h in air atmosphere. PbWO 4 powders were characterized by X-ray diffraction (XRD), Rietveld refinement, Fourier transform Raman (FT-Raman) spectroscopy and ultraviolet-visible (UV-vis) absorption spectroscopy measurements. XRD, Rietveld refinement and FT-Raman revealed that PbWO 4 powders are free of secondary phases and crystallizes in a tetragonal structure. The UV-vis absorption spectroscopy measurements suggest the presence of intermediary energy levels into the band gap of structurally disordered powders.
Materials Chemistry and Physics, 2009
MgTiO 3 powders were prepared by the complex polymerization method and heat treated at different ... more MgTiO 3 powders were prepared by the complex polymerization method and heat treated at different temperatures for 2 h. These powders were analyzed by X-ray diffraction (XRD), Rietveld refinements, micro-Raman (MR) spectroscopy, X-ray absorption near edge spectroscopy (XANES), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra showed that the crystalline powders have a rhombohedral structure. XANES spectra indicated that the local structure of crystalline MgTiO 3 powders is composed only by [TiO 6 ] clusters, while the disordered exhibit the simultaneous presence of both [TiO 5 ] and [TiO 6 ] complex clusters into the lattice. UV-vis spectra revealed different optical band gap values as a function of heat treatment temperature. This result can be an indicative of intermediary energy levels within the band gap of this material because of structural defects into the perovskite-type structure. PL behavior was attributed to the structural order-disorder and/or distortions on the [TiO 6 ]-[TiO 6 ] complex clusters.
Journal of Sol-Gel Science and Technology, 2009
Ba[Zr 0.25 Ti 0.75 ]O 3 (BZT) thin films were synthesized by the complex polymerization method an... more Ba[Zr 0.25 Ti 0.75 ]O 3 (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400°C for different times and at 700°C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultravioletvisible (UV-vis) absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT thin films heat treated at 700°C were approximately 148 and 0.08 at 1 MHz, respectively. UV-vis absorption spectra suggested the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was explained through the optical band gap values associated to the visible light emission components.
Journal of Physics D: Applied Physics, 2009
In this work, Ba(Zr 0.25 Ti 0.75 )O 3 ceramic was prepared by solid-state reaction. This material... more In this work, Ba(Zr 0.25 Ti 0.75 )O 3 ceramic was prepared by solid-state reaction. This material was characterized by x-ray diffraction and Fourier transform Raman spectroscopy. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurements indicated a diffuse phase transition. The broadening of the dielectric permittivity in the frequency range as well as its shifting at higher temperatures indicated a relaxor-like behaviour for this material. The diffusivity and the relaxation strength were estimated using the modified Curie-Weiss law. The optical properties were analysed by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements at room temperature. The UV-vis spectrum indicated that the Ba(Zr 0.25 Ti 0.75 )O 3 ceramic has an optical band gap of 2.98 eV. A blue PL emission was observed for this compound when excited with 350 nm wavelength. The polarity as well as the PL property of this material was attributed to the presence of polar [TiO 6 ] distorted clusters into a globally cubic matrix.
Journal of Physics and Chemistry of Solids, 2008
Intense and broad photoluminescence (PL) emission at room temperature was observed on structurall... more Intense and broad photoluminescence (PL) emission at room temperature was observed on structurally disordered Ba[Zr 0.25 Ti 0.75 ]O 3 (BZT) powders synthesized by the polymeric precursor method. BZT powders were annealed at 573 K for different times and at 973 K for 2 h in oxygen atmosphere. The single-phase cubic perovskite structure of the powder annealed at 973 K for 2 h was identified by X-ray diffraction and Fourier transform Raman techniques. PL emission increased with the increase of annealing time, which reached its maximum value in the powder annealed at 573 K for 192 h. First principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered models. The theoretical calculations and experimental measurements of Ultraviolet-visible absorption spectroscopy indicate that the presence of intermediary energy levels in the band gap is favorable for the intense and broad PL emission at room temperature in disordered BZT powders. The PL behavior is probably due the existence of a charge gradient on the disordered structure, denoted by means of a charge transfer process from [TiO 5 ]-[ZrO 6 ] or [TiO 6 ]-[ZrO 5 ] clusters to [TiO 6 ]-[ZrO 6 ] clusters. r
Journal of Materials Science, 2014
Rare earth samarium (Sm)-doped barium zirconate titanate (Ba 1-x Sm 2x/3 )(Zr 0.3 Ti 0.7 )O 3 (x ... more Rare earth samarium (Sm)-doped barium zirconate titanate (Ba 1-x Sm 2x/3 )(Zr 0.3 Ti 0.7 )O 3 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were prepared using solid state reaction (SSR) route. The structural and microstructural characterizations of the materials were done by using X-ray diffraction and SEM analysis, respectively. Rietveld refinement technique employed to investigate the details of crystal structure revealed singlephase cubic perovskite structure belonging to space group Pm-3m. Microstructure of the doped ceramics were found to be porous and of irregular shape and size along with aggregative characteristic. FTIR technique was employed to study the influence of additives in ceramics compositions and to investigate the displacement of M-O bonds. Raman spectroscopic study revealed that the substitution of Ba 2? ions by Sm 3? ions shifted the Raman-active modes toward higher energy, which indicated that these materials undergo an increase in average cubicity with increase in Sm 3? ion concentration. The temperature dependence of dielectric properties was investigated in the frequency range from 1 kHz to 1 MHz. The dielectric measurement indicated a diffuse type of phase transition (DPT). The broadening in the dielectric permittivity and frequency dependence behavior with increase in frequency indicated a relaxor behavior of these materials. The relaxation strength of these materials was well adjusted by using the Vogel-Fulcher relation.
Journal of Colloid and Interface Science, 2009
SrWO 4 powders were synthesized by the co-precipitation method and processed in a microwavehydrot... more SrWO 4 powders were synthesized by the co-precipitation method and processed in a microwavehydrothermal (MH) at 140 • C for different times. The obtained powders were analyzed by X-ray diffraction (XRD), micro-Raman (MR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM), ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra showed that the SrWO 4 powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a high absorption band situated at 831.57 cm −1 , which was ascribed to the W-O antisymmetric stretching vibrations into the [WO 4 ] tetrahedron groups. FEG-SEM micrographs suggested that the processing time is able to influence in the growth process and morphology of SrWO 4 powders. UV-vis absorption spectra revealed different optical band gap values for these powders. A green PL emission at room temperature was verified in SrWO 4 powders when excited with 488 nm wavelength.
Journal of Alloys and Compounds, 2009
Bismuth titanate, Bi 4 Ti 3 O 12 (BiT) powders were synthesized by the complex polymerization met... more Bismuth titanate, Bi 4 Ti 3 O 12 (BiT) powders were synthesized by the complex polymerization method. The structural evolution as a function of heat treatment temperature of these powders was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were verified by ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra revealed that the BiT powders heat treated at 700 • C for 2 h under oxygen flow crystallize in an orthorhombic structure without deleterious phases. UV-vis spectra indicated the presence of intermediary energy levels within the band gap of the powders heat treated at low temperatures. The maximum PL emissions of these materials were verified at around 598 nm, when excited by 488 nm wavelengths. Also, it was observed the presence of two broad PL bands, which were attributed to the intermediary energy levels arising from ␣-Bi 2 O 3 and BiT phases. 18] observed a tetragonal structure for this material below 600 • C and an orthorhombic structure at 750 • C. In the last years, different synthesis methods have been reported in the literature for the obtention of BiT powders, mainly including: solid-state reaction , high-energy ball milling process , self-propagating high-temperature , molten salts [24] and flash creation . In contrast, these methods present some drawbacks, such as: formation of secondary phases, contamination by impurities, high heat treatment temperatures, long processing times and nonuniform particle size distribution. A possible alternative for reduction of these problems can be the use of wet chemical methods, such as: sol-gel , citrate gel [29], urea precipitation [30], oxalate coprecipitation [31-33], hydrothermal [34-36], metalorganic decomposition [37] and polymeric precursor [38], hydrolysis . Moreover, these synthesis methods are able to improve the dielectrical, structural, morphological and mechanical properties of BiT oxides .
Journal of Alloys and Compounds, 2009
Intense blue and green photoluminescence (PL) emissions were observed at room temperature in bari... more Intense blue and green photoluminescence (PL) emissions were observed at room temperature in barium zirconate (BaZrO 3 ) powders prepared by chemical method. The powders were analyzed by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption spectroscopy (EXAFS) and ultraviolet-visible (UV-vis) absorption spectroscopy. The XRD patterns indicated the presence of a secondary phase of BaCO 3 in BaZrO 3 powders heat treated at 773 K. K-edge XANES data revealed that Zr atoms presents in at least two Zr environments. EXAFS investigations showed strong bond length dispersion in the first coordination shell around Zr atoms. EXAFS analysis indicated that Zr atoms are coordinated by 6 oxygen in BaZrO 3 powders heat treated at 973 K. UV-vis measurements suggested the presence of intermediary energy levels into the band gap of BaZrO 3 powders heat treated at 773 K. The intense PL emission in BaZrO 3 powders can be attributed to the two Zr environments or ZrO 5 -ZrO 6 clusters.