The authors present results of fluorescence line narrowing (FLN) and lifetime studies of Eu{sup 3... more The authors present results of fluorescence line narrowing (FLN) and lifetime studies of Eu{sup 3+}-doped ormosils prepared from Si(OCH{sub 3}){sub 4} and CH{sub 3}Si(OCH{sub 3}){sub 3}, (CH{sub 3}){sub 2}Si(OCH{sub 3}){sub 2}, (C{sub 2}H{sub 5}){sub 2}Si(OCH{sub 3}){sub 2}, and (n-C{sub 3}H{sub 7})Si(OCH{sub 3}){sub 3} in various proportions. Similar results are also presented for Eu{sup 3+}-doped gels derived from Si(OCH{sub 3}){sub 4} and fluorinated Eu{sup 3+} precursors (Eu(fod){sub 3}, (CF{sub 3}SO{sub 3}){sub 3}Eu, and (CF{sub 3}CO{sub 2}){sub 3}Eu{center_dot}3H{sub 2}O). The FLN studies indicated that significant Eu{sup 3+} clustering occurs in densified samples of both the organically modified and fluorinated compositions. Lifetime studies of the organically modified compositions showed longer Eu{sup 3+} lifetimes at low heat treatment temperatures relative to an unmodified sample. The difference in lifetime between modified and unmodified compositions decreased at high hea...
In the present work,we report our results for the sol–gel preparation and optical properties of C... more In the present work,we report our results for the sol–gel preparation and optical properties of CdS nanometer sized particles and Mn 2þ -doped CdS particles in silica-type glass matrices. Gels containing 4.5 wt.% CdO in 95.5SiO2 and 4.5Na2O–18B2O3–73.5SiO2 matrices were prepared through a hydrolysis of tetraethoxysilane,cadmium acetate and,in the sodium borosilicate composition,boron ethoxide and sodium acetate. We designed several heat treatments in H 2S to convert CdO to CdS in the gels. The influence of the heat treatment conditions on the optical properties of the nanoparticle semiconductor materials was studied using transmission electron microscopy,absorption,and temperature-dependent photoluminescence. A model of the photoluminescence processes was proposed to explain the observed emission bands. 2002 Elsevier Science B.V. All rights reserved.
The aim of this work was to evaluate in an open, noncomparative study the use of secnidazole in o... more The aim of this work was to evaluate in an open, noncomparative study the use of secnidazole in oral suspension given to Venezuelan children infected with Giardia intestinalis, from a community in Carapita, a slum area in Caracas. Seventy children from 2 to 11 years old (38 males and 32 females) were treated with a single oral dose of secnidazole (30 mg/Kg of body weight), after clinical and parasitological evaluation to make the diagnosis of active giardiasis. The effectiveness of treatment was determined by clinical examination and parasitological evaluation of feces samples 15 days after treatment. The results showed 95% of clinical cure with a significant decrease of the frequency of gastrointestinal symptoms. The parasitological cure was 98%, there were 4 failures at the end of treatment. Side effects observed after treatment were of mild intensity, lasting only few hours. These results show that a simple dose of secnidazole in an oral suspension is an effective, safe and well ...
ABSTRACTGlasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3-SiO2 ... more ABSTRACTGlasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3-SiO2 were prepared from metal alkoxide solution using the sol-gel process. After low temperature heat treatment in air, the glasses were heated up to 800 °C under a flowing H2 atmosphere to reduce Sm3+ into Sm2+. Samarium ions in the divalent and trivalent states were identified by fluorescence measurements. The fluorescence properties of Sm2+ions are discussed in relation to concentration of Sm2O3 and the glass matrix composition. Preliminary results of pressure studies on the luminescence spectra and lifetime of Sm2+ in the glasses are presented as well.
In this work, the single source organometallic precursor Bu4Sn6S6 was impregnated and decomposed ... more In this work, the single source organometallic precursor Bu4Sn6S6 was impregnated and decomposed on the surface of TiO2 to produce semiconductor composites. 119Sn Mössbauer, Raman and ultra violet/visible spectroscopies, powder X-ray diffraction, temperature programmed reduction and surface area suggest for Sn contents of 1, 5 and 10wt%, the formation of a highly dispersed unstable SnS phase which is readily oxidized
Silica–titania composite materials containing 20mol% TiO2 were prepared by sol–gel process using ... more Silica–titania composite materials containing 20mol% TiO2 were prepared by sol–gel process using tetraethoxysilane (TEOS) and titanium isopropoxide (Ti(OPr)4) as precursors. A two-stage hydrolysis procedure was performed in acid conditions for preparation of the TiO2–SiO2 oxides. Nanometer sized crystallites of CdS were incorporated into TiO2–SiO2 matrices by complex formation with thiourea, SC(NH2)2. The influence of the preparation route and calcination temperature
... Brandon T. Stone, Vilma C. Costa, and ... 34 upon switching the precursor from europium nitra... more ... Brandon T. Stone, Vilma C. Costa, and ... 34 upon switching the precursor from europium nitrate to europium triflate, but all of the lifetimes reported in ref 34 are shorter than the corresponding lifetimes measured in the current study, including those measured at room temperature. ...
Although there are various commercially available methods for the separation and capture of gas s... more Although there are various commercially available methods for the separation and capture of gas species such as CO2 and H2, they are energy expensive and in some cases environmentally unfriendly. The membrane separation process presents advantages such as its relative simplicity, ease of use, low energy consumption, and application in the separation of both liquid and gas mixtures. For these
Materials Research-ibero-american Journal of Materials, 2007
Tissue engineering has evolved from the use of biomaterials for bone substitution that fulfill th... more Tissue engineering has evolved from the use of biomaterials for bone substitution that fulfill the clinical demands of biocompatibility, biodegradability, non-immunogeneity, structural strength and porosity. Porous scaffolds have been developed in many forms and materials, but few reached the need of adequate physical, biological and mechanical properties. In the present paper we report the preparation of hybrid porous polyvinyl alcohol (PVA)/bioactive glass through the sol-gel route, using partially and fully hydrolyzed polyvinyl alcohol, and perform structural characterization. Hybrids containing PVA and bioactive glass with composition 58SiO2-33CaO-9P2O5 were synthesized by foaming a mixture of polymer solution and bioactive glass sol-gel precursor solution. Sol-gel solution was prepared from mixing tetraethoxysilane (TEOS), triethylphosphate (TEP), and calcium chloride as chemical precursors. The hybrid composites obtained after aging and drying at low temperature were chemically and morphologically characterized through infrared spectroscopy and scanning electron microscopy. The degree of hydrolysis of PVA, concentration of PVA solution and different PVA-bioglass composition ratios affect the synthesis procedure. Synthesis parameters must be very well combined in order to allow foaming and gelation. The hybrid scaffolds obtained exhibited macroporous structure with pore size varying from 50 to 600 µm.
Gels have been investigated as potential matrices for rare earth luminescence. The use of complex... more Gels have been investigated as potential matrices for rare earth luminescence. The use of complexing ligands in the sol-gel synthesis of the rare-earth doped glasses has been suggested to improve the rare earth ion luminescence properties in these matrices due to the changes in the local environment experienced by the rare earth ion. In this work, transparent Eu3+-doped gels were prepared from Si(OCH3)4 and fluorinated and/or complex-forming Eu3+ precursors (Eu(fod)3, (CF3 SO3)3Eu, (CF3CO2)Eu · 3H2O, Eu(thd)3 and Eu(acac)3). Results of emission, fluorescence line narrowing and lifetimes studies of Eu3+-doped gels derived from Si(OCH3)4 and fluorinated/chelate Eu3+ precursors are presented. The results were interpreted in terms of the evolution of the Eu3+ fluorescence in systems varying from solutions to the gels densified to 800°C. Analysis of the fluorescence decays of the 5D0 state suggests that the use of the fluorinated Eu3+ precursors reduces the hydrophobic content in the silica gels matrices. FLN studies indicate that Eu3+ clustering occurred in all densified samples.
Gels and glasses in the SiO2–Al2O3–ZnO–Cr2O3 and SiO2–Al2O3–MgO–Cr2O3 systems were synthesized by... more Gels and glasses in the SiO2–Al2O3–ZnO–Cr2O3 and SiO2–Al2O3–MgO–Cr2O3 systems were synthesized by the sol–gel method. A description of the change of the Cr3+ environment during the xerogel–glass–glass ceramic transformation is presented using optical properties of Cr3+ ions. Absorption and emission spectra, electron paramagnetic resonance measurements, and site-selective laser spectroscopy were performed to characterize the Cr3+ fluorescent centers. Absorption and fluorescence
The fluorescence properties of inorganic and organically-modified rare-earth-doped sol-gel silica... more The fluorescence properties of inorganic and organically-modified rare-earth-doped sol-gel silica are presented. Eu3+-doped ormosils were prepared from Si(OCH3)4 and CH3Si(OCH3)3, (CH3)2Si(OCH3)2, (CH3)2Si(OC2H5)2, or (n-C3H7)Si(OCH3)3 in various proportions. Er3+-doped ormosils were prepared using Si(OC2H5)4 and CH3Si(OC2H5)3, (CH3)2Si(OC2H5)2 or C2H5Si(OC2H5)3. Gels derived from Si(OCH3)4 were also doped with the fluorinated Eu3+ precursors Eu(fod)3, (CF3SO3)3Eu, and (CF3CO2)3Eu·3H2O. The effect of metal ion codopants, which are known to inhibit clustering of Eu3+ in sol-gel silica, on Er3+ fluorescence is also considered. Fluorescence line-narrowing studies of Eu3+-doped samples indicated that significant Eu3 clustering occurs in both the ormosils and fluorinated precursor compositions. Lifetime measurements of the Eu3+-and Er3+ –doped ormosils showed longer lifetimes at low heat treatment temperatures relative to purely inorganic sol-gel silica, but no significant difference remained in fully densified samples. The longest lifetimes were observed for samples doped with the fluorinated precursors, indicating that the fluorinated ligands are effective at reducing the water content in densified gels.
Revista Dental Press De Ortodontia E Ortopedia Facial, 2007
AIM: Two comercial brands of auto polymerizing acrylic resins (one for orthodontics use, Orto Cri... more AIM: Two comercial brands of auto polymerizing acrylic resins (one for orthodontics use, Orto Cril®, and the other for prosthetics use, Jet®) were analyzed concerning the amount of methyl methacrilate (MMA) monomer dissolved in solution, processed under and not under pressure, in different intervals (0.083; 0.25; 1; 1.25; 2.17; 5; 9; 14 and 21 days). METHODS: The ultra-violet absorption spectroscopy was used in the analysis of aqueous solutions of MMA, with known concentrations, in order to determine the calibration curve. Aqueous solutions containing samples made with the acrylic resins described above were submitted to ultra-violet absorption spectroscopy analysis. RESULTS AND CONCLUSIONS: The results were compared to the calibration curve data, in order to establish the MMA concentration. These results led to the conclusion that the residual MMA level dissolved in the solution was higher in the first twenty-four hours, tending to stability from this period on. Auto polymerizing acrylic resins processed under pressure showed higher levels of MMA, even though it was not noticed an interaction effect between the resins brand and the presence of pressure in the level of MMA concentration measured throughout the intervals. In spite of that, the three variables (time, resins and pressure) were of noticeable importance.
The authors present results of fluorescence line narrowing (FLN) and lifetime studies of Eu{sup 3... more The authors present results of fluorescence line narrowing (FLN) and lifetime studies of Eu{sup 3+}-doped ormosils prepared from Si(OCH{sub 3}){sub 4} and CH{sub 3}Si(OCH{sub 3}){sub 3}, (CH{sub 3}){sub 2}Si(OCH{sub 3}){sub 2}, (C{sub 2}H{sub 5}){sub 2}Si(OCH{sub 3}){sub 2}, and (n-C{sub 3}H{sub 7})Si(OCH{sub 3}){sub 3} in various proportions. Similar results are also presented for Eu{sup 3+}-doped gels derived from Si(OCH{sub 3}){sub 4} and fluorinated Eu{sup 3+} precursors (Eu(fod){sub 3}, (CF{sub 3}SO{sub 3}){sub 3}Eu, and (CF{sub 3}CO{sub 2}){sub 3}Eu{center_dot}3H{sub 2}O). The FLN studies indicated that significant Eu{sup 3+} clustering occurs in densified samples of both the organically modified and fluorinated compositions. Lifetime studies of the organically modified compositions showed longer Eu{sup 3+} lifetimes at low heat treatment temperatures relative to an unmodified sample. The difference in lifetime between modified and unmodified compositions decreased at high hea...
In the present work,we report our results for the sol–gel preparation and optical properties of C... more In the present work,we report our results for the sol–gel preparation and optical properties of CdS nanometer sized particles and Mn 2þ -doped CdS particles in silica-type glass matrices. Gels containing 4.5 wt.% CdO in 95.5SiO2 and 4.5Na2O–18B2O3–73.5SiO2 matrices were prepared through a hydrolysis of tetraethoxysilane,cadmium acetate and,in the sodium borosilicate composition,boron ethoxide and sodium acetate. We designed several heat treatments in H 2S to convert CdO to CdS in the gels. The influence of the heat treatment conditions on the optical properties of the nanoparticle semiconductor materials was studied using transmission electron microscopy,absorption,and temperature-dependent photoluminescence. A model of the photoluminescence processes was proposed to explain the observed emission bands. 2002 Elsevier Science B.V. All rights reserved.
The aim of this work was to evaluate in an open, noncomparative study the use of secnidazole in o... more The aim of this work was to evaluate in an open, noncomparative study the use of secnidazole in oral suspension given to Venezuelan children infected with Giardia intestinalis, from a community in Carapita, a slum area in Caracas. Seventy children from 2 to 11 years old (38 males and 32 females) were treated with a single oral dose of secnidazole (30 mg/Kg of body weight), after clinical and parasitological evaluation to make the diagnosis of active giardiasis. The effectiveness of treatment was determined by clinical examination and parasitological evaluation of feces samples 15 days after treatment. The results showed 95% of clinical cure with a significant decrease of the frequency of gastrointestinal symptoms. The parasitological cure was 98%, there were 4 failures at the end of treatment. Side effects observed after treatment were of mild intensity, lasting only few hours. These results show that a simple dose of secnidazole in an oral suspension is an effective, safe and well ...
ABSTRACTGlasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3-SiO2 ... more ABSTRACTGlasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3-SiO2 were prepared from metal alkoxide solution using the sol-gel process. After low temperature heat treatment in air, the glasses were heated up to 800 °C under a flowing H2 atmosphere to reduce Sm3+ into Sm2+. Samarium ions in the divalent and trivalent states were identified by fluorescence measurements. The fluorescence properties of Sm2+ions are discussed in relation to concentration of Sm2O3 and the glass matrix composition. Preliminary results of pressure studies on the luminescence spectra and lifetime of Sm2+ in the glasses are presented as well.
In this work, the single source organometallic precursor Bu4Sn6S6 was impregnated and decomposed ... more In this work, the single source organometallic precursor Bu4Sn6S6 was impregnated and decomposed on the surface of TiO2 to produce semiconductor composites. 119Sn Mössbauer, Raman and ultra violet/visible spectroscopies, powder X-ray diffraction, temperature programmed reduction and surface area suggest for Sn contents of 1, 5 and 10wt%, the formation of a highly dispersed unstable SnS phase which is readily oxidized
Silica–titania composite materials containing 20mol% TiO2 were prepared by sol–gel process using ... more Silica–titania composite materials containing 20mol% TiO2 were prepared by sol–gel process using tetraethoxysilane (TEOS) and titanium isopropoxide (Ti(OPr)4) as precursors. A two-stage hydrolysis procedure was performed in acid conditions for preparation of the TiO2–SiO2 oxides. Nanometer sized crystallites of CdS were incorporated into TiO2–SiO2 matrices by complex formation with thiourea, SC(NH2)2. The influence of the preparation route and calcination temperature
... Brandon T. Stone, Vilma C. Costa, and ... 34 upon switching the precursor from europium nitra... more ... Brandon T. Stone, Vilma C. Costa, and ... 34 upon switching the precursor from europium nitrate to europium triflate, but all of the lifetimes reported in ref 34 are shorter than the corresponding lifetimes measured in the current study, including those measured at room temperature. ...
Although there are various commercially available methods for the separation and capture of gas s... more Although there are various commercially available methods for the separation and capture of gas species such as CO2 and H2, they are energy expensive and in some cases environmentally unfriendly. The membrane separation process presents advantages such as its relative simplicity, ease of use, low energy consumption, and application in the separation of both liquid and gas mixtures. For these
Materials Research-ibero-american Journal of Materials, 2007
Tissue engineering has evolved from the use of biomaterials for bone substitution that fulfill th... more Tissue engineering has evolved from the use of biomaterials for bone substitution that fulfill the clinical demands of biocompatibility, biodegradability, non-immunogeneity, structural strength and porosity. Porous scaffolds have been developed in many forms and materials, but few reached the need of adequate physical, biological and mechanical properties. In the present paper we report the preparation of hybrid porous polyvinyl alcohol (PVA)/bioactive glass through the sol-gel route, using partially and fully hydrolyzed polyvinyl alcohol, and perform structural characterization. Hybrids containing PVA and bioactive glass with composition 58SiO2-33CaO-9P2O5 were synthesized by foaming a mixture of polymer solution and bioactive glass sol-gel precursor solution. Sol-gel solution was prepared from mixing tetraethoxysilane (TEOS), triethylphosphate (TEP), and calcium chloride as chemical precursors. The hybrid composites obtained after aging and drying at low temperature were chemically and morphologically characterized through infrared spectroscopy and scanning electron microscopy. The degree of hydrolysis of PVA, concentration of PVA solution and different PVA-bioglass composition ratios affect the synthesis procedure. Synthesis parameters must be very well combined in order to allow foaming and gelation. The hybrid scaffolds obtained exhibited macroporous structure with pore size varying from 50 to 600 µm.
Gels have been investigated as potential matrices for rare earth luminescence. The use of complex... more Gels have been investigated as potential matrices for rare earth luminescence. The use of complexing ligands in the sol-gel synthesis of the rare-earth doped glasses has been suggested to improve the rare earth ion luminescence properties in these matrices due to the changes in the local environment experienced by the rare earth ion. In this work, transparent Eu3+-doped gels were prepared from Si(OCH3)4 and fluorinated and/or complex-forming Eu3+ precursors (Eu(fod)3, (CF3 SO3)3Eu, (CF3CO2)Eu · 3H2O, Eu(thd)3 and Eu(acac)3). Results of emission, fluorescence line narrowing and lifetimes studies of Eu3+-doped gels derived from Si(OCH3)4 and fluorinated/chelate Eu3+ precursors are presented. The results were interpreted in terms of the evolution of the Eu3+ fluorescence in systems varying from solutions to the gels densified to 800°C. Analysis of the fluorescence decays of the 5D0 state suggests that the use of the fluorinated Eu3+ precursors reduces the hydrophobic content in the silica gels matrices. FLN studies indicate that Eu3+ clustering occurred in all densified samples.
Gels and glasses in the SiO2–Al2O3–ZnO–Cr2O3 and SiO2–Al2O3–MgO–Cr2O3 systems were synthesized by... more Gels and glasses in the SiO2–Al2O3–ZnO–Cr2O3 and SiO2–Al2O3–MgO–Cr2O3 systems were synthesized by the sol–gel method. A description of the change of the Cr3+ environment during the xerogel–glass–glass ceramic transformation is presented using optical properties of Cr3+ ions. Absorption and emission spectra, electron paramagnetic resonance measurements, and site-selective laser spectroscopy were performed to characterize the Cr3+ fluorescent centers. Absorption and fluorescence
The fluorescence properties of inorganic and organically-modified rare-earth-doped sol-gel silica... more The fluorescence properties of inorganic and organically-modified rare-earth-doped sol-gel silica are presented. Eu3+-doped ormosils were prepared from Si(OCH3)4 and CH3Si(OCH3)3, (CH3)2Si(OCH3)2, (CH3)2Si(OC2H5)2, or (n-C3H7)Si(OCH3)3 in various proportions. Er3+-doped ormosils were prepared using Si(OC2H5)4 and CH3Si(OC2H5)3, (CH3)2Si(OC2H5)2 or C2H5Si(OC2H5)3. Gels derived from Si(OCH3)4 were also doped with the fluorinated Eu3+ precursors Eu(fod)3, (CF3SO3)3Eu, and (CF3CO2)3Eu·3H2O. The effect of metal ion codopants, which are known to inhibit clustering of Eu3+ in sol-gel silica, on Er3+ fluorescence is also considered. Fluorescence line-narrowing studies of Eu3+-doped samples indicated that significant Eu3 clustering occurs in both the ormosils and fluorinated precursor compositions. Lifetime measurements of the Eu3+-and Er3+ –doped ormosils showed longer lifetimes at low heat treatment temperatures relative to purely inorganic sol-gel silica, but no significant difference remained in fully densified samples. The longest lifetimes were observed for samples doped with the fluorinated precursors, indicating that the fluorinated ligands are effective at reducing the water content in densified gels.
Revista Dental Press De Ortodontia E Ortopedia Facial, 2007
AIM: Two comercial brands of auto polymerizing acrylic resins (one for orthodontics use, Orto Cri... more AIM: Two comercial brands of auto polymerizing acrylic resins (one for orthodontics use, Orto Cril®, and the other for prosthetics use, Jet®) were analyzed concerning the amount of methyl methacrilate (MMA) monomer dissolved in solution, processed under and not under pressure, in different intervals (0.083; 0.25; 1; 1.25; 2.17; 5; 9; 14 and 21 days). METHODS: The ultra-violet absorption spectroscopy was used in the analysis of aqueous solutions of MMA, with known concentrations, in order to determine the calibration curve. Aqueous solutions containing samples made with the acrylic resins described above were submitted to ultra-violet absorption spectroscopy analysis. RESULTS AND CONCLUSIONS: The results were compared to the calibration curve data, in order to establish the MMA concentration. These results led to the conclusion that the residual MMA level dissolved in the solution was higher in the first twenty-four hours, tending to stability from this period on. Auto polymerizing acrylic resins processed under pressure showed higher levels of MMA, even though it was not noticed an interaction effect between the resins brand and the presence of pressure in the level of MMA concentration measured throughout the intervals. In spite of that, the three variables (time, resins and pressure) were of noticeable importance.
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