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An experimental-theoretical approach is proposed to investigate the size-dependent photobleaching of colloidal semiconductor quantum dots (QDs) excited by a nanosecond pulsed laser. In the experimental background, the ground-state absorption and photoluminescence (PL) spectra of chemically prepared QDs are monitored over an excitation time at distinct laser irradiances. The magnitude of photobleaching in the QD solution is quantified by the decay rate of the PL signal as a function of the excitation time and the laser power. A theoretical spectroscopy model is then used to estimate the particle size distribution (PSD) in colloidal solution from the absorption data generated at different laser powers. The resulting evolution of the PSD of the QD ensemble under irradiation is analyzed in terms of classical crystallization theories dealing with the formation, growth, and dissolution of colloidal particles in a supersaturated medium. The QD response to laser irradiation is also interpreted by a simple mechanical model that correlates the photoinduced hydrostatic strain at the solid/liquid interface and the predicted variation of the mean particle size. The reported experimental and theoretical methods are used to completely elucidate the basic physico-chemical processes responsible for the laser-induced photobleaching kinetics of glutathione-capped CdTe aqueous QDs with very small mean sizes. For this purpose, we synthesized a series of colloidal QD samples with mean particle diameters ranging from 1.95 to 2.68 nm. Our results indicate that a faster photobleaching rate occurs in QD samples with smaller sizes in which particle dissolution under laser irradiation is predominant. On the other hand, the photobleaching rate becomes slower in samples with larger dot sizes, possibly due to the formation of core/shell structures in solution via thermal degradation of thiol ligands either during the chemical synthesis or as a consequence of the subsequent interaction with the excitation laser.

Lead (Pb) halide perovskite nanocrystals, with the general formula APbX

The research on development of materials with higher efficient photoluminescent properties, is the aim of several researchers around the world. Photoluminescent materials containing Rare Earths (RE3+) can be applied in various technological sectors, mainly in light emitting devices. In this sense, this work reports on obtaining of polymeric membranes based on chitosan and gelatin containing [Eu (TTA)3(H2O)2] on the surface. The materials presented high intensity of photoluminescence emission with narrow bands attributed to the intraconfigurational 4f transitions of Eu3+. To keep the material in the desiccator containing silica gel, showed the loss of water molecule, in which contributed significantly with the intensity of emission. The lifetime values showed values between 0.42 and 0.55 ms, higher than many values reported in literature. The surface morphology of the materials showed a homogeneous profile free of cracks. The materials presented interesting photoluminescent properties that make them candidates for possible application in lighting or imaging devices.

The cytotoxic and genotoxic effects of commercial endodontic sealers (AH Plus, Sealer 26 and Endomethasone N) incorporated with nanostructured silver vanadate decorated with silver nanoparticles (AgVO3 - at concentrations 2.5, 5, and 10%) on human gingival fibroblast (HGF), and the silver (Ag+ ) and vanadium (V4+ /V5+ ) ions release were evaluated. Cytotoxicity, cell death, and genotoxicity tests were carried out with extract samples of 24-hr and 7-days. The release of Ag+ and V4+ /V5+ was evaluated. Cytotoxicity in HGF was caused by AH Plus (AP) with 5 and 10% of AgVO3 (83.84 and 67.49% cell viability, respectively) with 24-hr extract (p

This in vitro study aimed to investigate the effect of incorporating the semiconductor nanostructured silver vanadate decorated with silver nanoparticles (β-AgVO3) in a dual-cure resin cement on the degree of conversion (DC), microhardness, roughness, color, adhesion properties before and after artificial aging, and antimicrobial efficacy.Three test groups were established: control (without β-AgVO3), with the incorporation of 2.5% and 5% (by weight) of β-AgVO3 in dual-cure resin cement (Allcem, FGM). The degree of conversion was measured using Fourier transform infrared spectroscopy (FTIR). To evaluate roughness (n = 10), microhardness (n = 10), color (n = 10), and to perform agar disk diffusion (n = 8), disks of 6-mm diameter and 2-mm height were manufactured using the same concentrations. For the color and shear bond strength test (n = 6), orthodontic brackets (Morelli) were used, which were cemented to natural human enamel and evaluated before and after artificial aging via thermocycling at 5°C and 55°C for 1000 cycles. For color measurements, a portable spectrocolorimeter and the CIE-Lab method were used. Data were analyzed using Student's t-test, ANOVA, and Tukey's multiple comparisons with significance set at α = 0.05.Semiconductor incorporation did not influence the cements's DC. The incorporation of 2.5% and 5% of β-AgVO3 resulted in a significant increase in Knoop microhardness and surface roughness. Significant changes were observed in the color of the specimens when the semiconductor was incorporated. Adhesion after aging remained within the clinically recommended values in all groups, and antimicrobial activity was observed against Staphylococcus aureus, Streptococcus mutans, and Enterococcus faecalis at both concentrations tested.It is suggested to incorporate the semiconductor β-AgVO3 in the dual-cure resin cement at both concentrations. Moreover, the physical-mechanical properties remained satisfactory for the proposed application.

Copper indium sulfide quantum dots (QDs) have attracted substantial attention in recent years due to environmental issues and diverse applications. We report the synthesis and characterization of c...

Lead halide perovskites have emerged as promising materials for light-emitting devices. Here, we report the preparation of colloidal CsPbBr3 nanoplatelets (3 × 4 × 23 nm3) experiencing a strong qua...

CdTe/CdS core/shell quantum dots (QDs) are formed in aqueous synthesis via the partial decomposition of hydrophilic thiols, used as surface ligands. In this work, we investigate the influence of the chemical nature (functional group and chain length) of the used surface ligands on the shell formation. Four different surface ligands are compared: 3-mercaptopropionic acid, MPA, thioglycolic acid, TGA, sodium 3-mercaptopropanesulfonate, MPS, and sodium 2-mercaptoethanesulfonate, MES. The QD growth rate increases when the ligand aliphatic chain length decreases due to steric reasons. At the same time, the QDs stabilized with carboxylate ligands grow faster and achieve higher photoluminescence quantum yields compared to those containing sulfonate ligands. The average PL lifetime of TGA and MPA capped QDs is similar (≈20 ns) while in the case of MPS shorter (≈15 ns) and for MES significantly longer (≈30 ns) values are measured. A detailed structural analysis combining powder X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) indicates the existence of two novel regimes of band alignment: in the case of the mercaptocarboxylate ligands the classic type I band alignment between the core and shell materials is predominant, while the mercaptosulfonate ligands induce a quasi-type II alignment (MES) or an inverted type I alignment (MPS). Finally, the effect of the pH value on the optical properties was evaluated: using a ligand excess in solution allows achieving better stability of the QDs while maintaining high photoluminescence intensity at low pH.

In this work, the Er3+-doped Sr2CeO4 phosphors are reported, synthesized through a facile combustion method using citric acid as organic precursor, Ag+ as a cationic charge compensator and as a stabilizer of the photoluminescent phase of interest. FTIR, XRD and SEM results indicate the formation of the Sr2CeO4 with a high purity of phase obtained by this methodology. The spectral downshifting properties of the materials were investigated exciting the materials at UV-region. Emission spectra present a broad band emission positioned at 467 nm assigned to the cerate inorganic material phase and Er3+ emission bands at 525, 550 and 667 nm, attributed to the Er3+ transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. The excited state of the Sr2CeO4 and 4S3/2 phases of Er3+ was shown to be directly dependent on the Er3+ concentration. The observed behavior indicates a direct relation of the photoluminescence between the matrix and the Er3+.The mechanism of energy transfer is proposed and presented in this work. The influence of the in situ heating on the photoluminescence properties of the materials was also investigated. The results reveal that these down converter Er3+ materials have potential for thermometric applications.

The search for new materials for application in energy production and conversion has identified inorganic oxides doped with rare earth ions as promising candidates for the construction of photovoltaic devices for energy conversion. This work presents the synthesis of TiO2 powders doped with Eu3+, using propylene glycol in the reaction medium, changing the europium percentage at 0.2, 3 and 7 mol%, and heat-treated at 700, 750, 800 and 900 °C for 8 h. The results of X-ray diffraction showed the formation of TiO2 polymorphs (anatase and rutile), both belonging to the tetragonal system and also the formation of europium titanate. The Rietveld refinement showed the deformation of the network parameters and volume of the unit cell, as well as the percent composition of the phases. Raman spectroscopy corroborated the results of XRD. Photoluminescence results showed that the synthesized materials have intense emission in the red region with the most intense band positioned at 614 nm assigned to the 5D0 → 7F2 transition of Eu3+ mainly in the sample with 3 mol% of Eu3+ heat-treated at 700 °C. The life time results showed that the photoluminescence of the materials are dependent on the crystalline structure, the host matrix in which the Eu3+ is localized, and the amount of the dopant in the sample. According to the results obtained in this work, the materials have the interesting downconversion effect, being a great absorber of UV–vis energy and converting that energy to the visible region. Materials with these photoluminescence properties associated with the structural properties are very interesting for use in the improvement of solar cells.

The present work describes the comparison of the optical and structural properties between CdTe quantum dots (QD) synthesized in water and in the binary solvent (water + glycerin) via one-pot approach synthesis. The optical properties of the nanocrystals obtained with different synthesis parameters were characterized by UV-visible and photoluminescence spectroscopies. The structural chracterization were performed by Fourier transform infrared spectroscopy (FTIR), zeta potential, size-distribution by dynamic light scattering (DLS), X-ray diffraction (XRD), and also by high-resolution transmission electron microscopy (HRTEM). The optical properties of CdTe QD when synthesized in the binary solvent were better, resulting in the increase of photoluminescence quantum yield (φƒ). The CdTe QD prepared in 120 min, at pH 10.0, in the Cd:Te molar ratio 20:1, using the molar ratio 1:1.5 of Cd:TGA (thioglycolic acid), exhibited a narrow photoluminescence band and enhanced φƒ for the samples synthesized in a binary solvent in comparison to water solvent (58.4 and 49.5%, respectively).

RESUMO Entre os nanomateriais de carbono, os pontos de carbono (PCs) estão entre os mais atraentes devido as suas interessantes propriedades fotoluminescentes. Os PCs apresentam processo de síntese fácil, possibilidade de funcionalização da superfície, baixa toxicidade, alta solubilidade em água e biocompatibilidade. Devido a isso, suas aplicações na área biomédica e de bioimagem tem se destacado na literatura. Neste trabalho, PCs foram sintetizados por dois métodos diferentes a partir da ovalbumina, o qual é um precursor não tóxico e composto predominantemente por aminoácidos de cadeia curta. Os PCs foram caracterizados por espectroscopias de absorção (UV-Vis), de emissão (fluorescência) e infravermelho (IVTF), além de análise termogravimétrica (ATG). Os PCs foram utilizados como sondas fluorescentes para uma imagem colorida (azul e verde) de células HEK293 e não induziram a morte celular, o que indica que os mesmos são biocompatíveis e não tóxicos para este tipo de células. Dessa forma, os resultados aqui apresentados demonstram que os PCs podem ser considerados potenciais substitutos para corantes comerciais em marcação biológica. ABSTRACT Among the carbon nanomaterials, carbon dots (CDs) are among the most attractive ones due to their interesting photoluminescent properties. PCs feature easy synthesis process, possibility of surface functionalization, low toxicity, high water solubility and biocompatibility. Because of this, their applications in the biomedical and bioimaging areas has been highlighted in literature. In this work, CDs were synthesized by two different methods using ovalbumin as precursor, which is a nontoxic reactant composed predominantly of short chain amino acids. The CDs were characterized by absorption (UV-Vis), emission (fluorescence), infrared (IRFT) spectroscopies, and thermogravimetric analysis (TGA). The CDs were used as fluorescent probes for multicolor (blue and green) imaging of HEK293 cells and did not induce to cell death, which indicates that the CDs are biocompatible and nontoxic to this type of cells. Therefore, the results presented here demonstrated that CDs can be considered as a potential substitute for commercial dyes in biological images.

A facile hydrothermal method to synthesize water-soluble copper indium sulfide (CIS) nanocrystals (NCs) at 150 &deg, C is presented. The obtained samples exhibited three distinct photoluminescence peaks in the red, green and blue spectral regions, corresponding to three size fractions, which could be separated by means of size-selective precipitation. While the red and green emitting fractions consist of 4.5 and 2.5 nm CIS NCs, the blue fraction was identified as in situ formed carbon nanodots showing excitation wavelength dependent emission. When used as light absorbers in quantum dot sensitized solar cells, the individual green and red fractions yielded power conversion efficiencies of 2.9% and 2.6%, respectively. With the unfractionated samples, the efficiency values approaching 5% were obtained. This improvement was mainly due to a significantly enhanced photocurrent arising from complementary panchromatic absorption.

Made available in DSpace on 2020-12-12T00:57:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-03-05 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Financiadora de Estudos e Projetos Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Inorganic oxides doped with RE3+ have interesting optical properties for converting photons into higher and/or lower energy from excitation, ultraviolet (UV) or infrared (IR). The luminescence materials Y2O3:Yb3+,Eu3+,Er3+ (xYb: 1.2; xEu: 2.0; xEr: 0.1–3.0 mol%) were successfully prepared using different precursors, NH4OH (ammonium hydroxide), H2C2O4 (oxalic acid), C6H8O7 (acid citrate) and CH4N2O (urea). The as prepared materials were annealed at 900, 1000 and 1100 °C. The crystalline structure and morphology of these materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV excited and upconversion photoluminescence. Structural investigation of materials exhibited formation of the cubic phase, indicating efficient doping ions in the matrix. In the analysis of the diffractograms, the use of the Scherrer equation showed the increase of the crystallite size by increasing the annealing temperature. There was also a small variation in the microstrain values of materials indicating the possible presence of structural defects. Photoluminescence investigations indicate that all the precursors used are favorable for the synthesis verified from the intense luminescence of the materials. Y2O3:Yb3+,Eu3+,Er3+ to be excited simultaneously at 394 and 980 nm, which exhibited emission narrow bands at 524 nm, 541 nm, 662 nm and 601 nm, 612 nm, assigned to the Er3+ and Eu3+ ion, respectively. There is a cross relaxation process due to decreased lifetime values (between 0.73 and 1.69 ms) when compared to materials doped with Eu3+ alone. In all materials, the amount of dopant was observed to not influence the morphology of the materials or the photoluminescent properties, providing potential applications in energy conversion, specific in solar cell. Grupo de Pesquisa em Química de Materiais (GPQM) Departamento de Ciências Naturais (DCNat) Universidade Federal de São João del Rei (UFSJ) Laboratório de Materiais Vítreos (LaMaV) Departamento de Engenharia de Materiais (DEMa) Universidade Federal de São Carlos (UFSCar) Department of Chemistry and Physics University of Tennessee at Martin Grupo de Química de Materiais Inorgânicos Nanoestruturados (GQMIN) Institute of Chemistry – (IQ) Federal University of Uberlândia – (UFU), Av. João Naves de Ávila, 2121 – Bairro Santa Mônica Desenvolvimento de Materiais Inorgânicos com Terras Raras – DeMITeR Laboratório de Materiais Fotoluminescentes (LAMAF) Institute of Chemistry – (IQ) Federal University of Uberlândia – (UFU), Av. João Naves de Ávila, 2121 – Bairro Santa Mônica Institute of Chemistry São Paulo State University (UNESP) Institute of Chemistry São Paulo State University (UNESP) CAPES: 001 FAPEMIG: CEX - RED-00010- 14

This paper reports citrate-stabilized silver nanoparticles (AgNPs) synthesized by nitrate ion chemical reduction with sodium borohydride, at different pHs (2–9). The AgNPs synthesized by this method exhibited size distribution from 5 to 249 nm, depending on pH, as determined by dynamic light scattering, and morphology spherical, as determined by transmission electron microscopy. In pH range 3–7 occurred aggregation of the nanoparticles. The size distribution depending on pH was determined by dynamic light scattering. The zeta potential was determined, and the colloidal stability was correlated with nanoparticles aggregation at different pHs. The size-dependent antimicrobial activity was evaluated for two solutions, wherein both samples exhibited antimicrobial activity, although the smallest AgNPs without agglomeration have enhanced antimicrobial properties. Keywords: Silver Nanoparticles, Zeta Potential, Dynamic Light Scattering, Size Distribution, Antimicrobial Activity.

Color tunable blue-white-red emitting CaY0.99-xTb0.01EuxAlO4 phosphors were prepared by an easy and low-cost chemical route using citric acid as precursor. The structural and morphological properties were evaluated by XRD and SEM techniques. The photoluminescence spectra and decay curves under excitation at 352 nm reveals the energy transfer process from Tb3+ to Eu3+. The dependence of temperature on energy transfer was evaluated, indicating higher efficiency as the temperature increases The dominant mechanism was demonstrated to be dipole-dipole type. By adjusting the excitation wavelength, the color emission of CaYAlO4:Tb3+,Eu3+solids can be tuned from blue to red, through white light. The cell viability of this materials was performed in the saccharomyces cerevisiae medium culture observing the biocompatibility with 160 and 320 μg/mL of concentration. In parallel the white emission performance was analyzed by determining the CIE coordinates and color correlated temperature (CCT). The CaY0.985Tb0.01Eu0.005AlO4 material showed CIE coordinates (0.327, 0334) and CCT = 5755 K, making this material an example of single-phase white emitting system.

Recently, a new class of materials, the Perovskite Nanocrystals, also known as perovskite quantum dots (PQDs) has emerged. Perovskite nanocrystals are promising in optoelectronics due to their quantum confinement properties, narrow photoluminescence bands with short decay times, optically tunable bandgaps, easy surface passivation and high photoluminescent quantum yields. The intense photoluminescence covering the entire visible region of the spectrum can be easily adjusted through the composition and/or the nanocrystals sizes. This paper presents the state-of-the-art of these materials, since their discovery to current research, including their synthesis methods, properties and applications.

Statement of problem Dental porcelain restorations are subject to biological failures related to secondary caries and periodontal disease leading to prosthesis replacement. Purpose The purpose of this in vitro study was to explore the microbiological and mechanical properties of dental porcelain incorporated with different percentages of silver vanadate (β-AgVO3) through microbiological analysis, roughness tests, and the Vickers microhardness test. Material and methods IPS InLine porcelain specimens were made by using a cylindrical Teflon matrix in the dimensions of 8×2 mm. For the control group, the porcelain was manipulated according to the manufacturer's instructions. The groups incorporating the nanomaterial were prepared with 2.5%, 5%, and 10% of β-AgVO3, which was added proportionally by mass to the porcelain powder. In vitro microbiologic analysis, roughness tests, and the Vickers microhardness test were performed. Results Against Streptococcus mutans, the control group showed no inhibition halo (0 mm). All groups with AgVO3 showed a zone of inhibition, the highest for the group with 10% (30 mm) and then the groups with 2.5% (9 mm) and 5% (17 mm). For Vickers microhardness, no statistically significant difference (P Conclusions Adding β-AgVO3 to dental porcelain demonstrated antimicrobial effectiveness at all concentrations (2.5%, 5%, and 10%), with no effect on Vickers microhardness. The 10% group had higher roughness than the other groups.

Incorporation of quantum dots (QDs) into porous matrices has triggered the development of novel optical devices. In this work, TiO2 sensitized by CdTe incorporated into bacterial nanocellulose (BNC) membranes were tested as photoelectrodes in a photoelectrochemical cell directed to the water splitting for hydrogen generation. The flexible membranes were produced by immersing BNC membranes in an aqueous solution of CdTe capped with glutathione (CdTe–GSH) and further deposited over a thin layer of TiO2. Incorporation of CdTe–GSH into BNC membranes was confirmed by infrared spectroscopy. Fluorescence spectroscopy revealed that the luminescence intensity increased with the immersion time in the CdTe–GSH solution. Field-emission gun scanning electron microscopy (FEG-SEM) images revealed that the CdTe/QDs (5 nm) were homogeneously dispersed on the cellulose nanofibers. BNC/CdTe–GSH membranes was tested as photoelectrodes. Photoelectrochemical cells exhibited a significant photocurrent in wavelengths ranging from 400 to 800 nm, which indicates their potential for applications as flexible electrodes, sensors and photovoltaic systems.

Sm 3+ doped SiO 2 -Gd 2 O 3 composites were obtained by a sol-gel process, and the ideal percentage of Sm 3+ was evaluated for bioimaging applications. By XRD, a formation of Gd 2 O 3 cubic materials was observed, and TEM shows that Gd 2 O 3 particles are dispersed in a SiO 2 lattice. PLE spectra confirm the main absorption bands in the UV region and emission shows the most efficient excitation at 275 nm. PL results reveal the incorporation of Sm 3+ in Gd 2 O 3 structures and lead to the understanding of the efficient energy transfer between Gd 3+ and Sm 3+ in the materials. The mechanism is proposed and discussed. CIE plotting shows color coordinates in the orange and red regions, mainly dependent on the excitation source. Sm 3+ positions in Gd 2 O 3 are discussed using the results obtained in the emission spectra. Materials presented high lifetime values, between 1.53 and 1.82 ms. The phosphors show tunability properties and better performance as red phosphors when excited at 275 nm. Cell viability was performed and the material is non-toxic. The materials were evaluated as biological markers, and present fluorescence under rhodamine emission filters. SiO 2 -Gd 2 O 3 :Sm 3+ demonstrates a good viability index and co-localizes with membrane cell markers, showing a promising material for cell tracking. The material also demonstrates potential for cancer targeting.

This work focuses on Sr2CeO4 materials containing Ag+ and Eu3+ that are obtained by a combustion method using citric acid as a precursor. The heat-treatment at 1100 °C was efficient and phase impurities are eliminated with presence of Ag+, favoring the Sr2CeO4 formation, as confirmed by XRD. SEM analysis shows a proportional decrease in the organization of particles as a function of doping material, with a nanorods morphology. Diffuse reflectance shows that materials are transparent at visible region, with absorption at UV region. Exciting Sr2CeO4-based materials at 270 nm, photoluminescence analysis reveal a band at 470 nm, characteristic of this material and, incorporating Eu3+, emission bands beyond 470 nm are observed characteristic of Eu3+. Eu3+ photoluminescence makes the Sr2CeO4 materials present color coordinates at bluish green, green, white, yellowish pink and reddish orange regions of electromagnetic spectra. Decay lifetimes of Sr2CeO4 and Eu3+ were determined and are discussed. The results obtained demonstrate materials with a high potential for application in light emitting devices, and a methodology efficient at obtaining these materials.

Terbium doped SiO2-Gd2O3 materials were obtained by a sol-gel process and heat-treated at 1000 °C. The effect of Tb3+concentration on structural, optical and photoluminescent properties of materials are reported here. FT-IR indicated the presence of Gd2O3 and SiO2 in the composition of materials. XRD showed the formation of the Gd2O3 cubic phase without the presence of phase impurities, and lattice parameter calculations indicated the effective inclusion of Tb3+ in Gd2O3 crystalline structure. SEM analysis revealed spherical particles of Gd2O3 and TEM confirmed that these particles are included in the amorphous SiO2. Excitation spectra show bands in the UV-region at characteristic wavelengths of the Gd2O3 host absorption. Emission spectra were collected by changing the excitation, and the intensity shows dependence on the UV photon energy. Tb3+-doped Gd2O3 grown into SiO2 showed higher Tb3+ lifetimes which are ideal for photonic applications. The temperature significantly influenced the luminescence of the materials, with chromaticity changing from green to blue region. The activation energy for thermal quenching (Ea) was determined by an Arrhenius methodology and the material shows a high thermal stability (Ea for thermal quenching = 0.378 eV).

In this work were synthesized highly luminescent carbon dots for use as fluorescence sensor for Cr(VI). Carbon dots (CDots) were prepared by pyrolysis of the mixture of molecular precursors as citric acid and reduced glutathione. Pyrolysis revealed to be a simple procedure that afforded CDots with a photoluminescence quantum yield of 69.4%, and particle size of about 2.5 nm. To explore the analytical potentiality of the nanomaterial produced, the CDots were applied as fluorescent sensors to determine Cr(VI) in water and soil samples. The interaction mechanism between CDots and Cr(VI) is associated with both inner filter effect and static quenching. After optimization of the main analytical parameters, the method showed a linear range of 0.10–12 μg mL −1 with limit of detection (LOD) of 0.03 μg mL −1 (pH 7), and recoveries of 90–105% and 99.5–107% for samples of water and soil, respectively. Thus, the method proved to be sensitive, fast and versatile for applications in different environmental samples.

We report the synthesis of novel multicolor photoluminescent carbon quantum dots (CQDs) from multi-wall carbon nanotubes, and their covalent functionalization with amines by peptide bonds. The resulting CQDs consisted of quasi-spherical graphite nanocrystals around 10 nm diameter, which were capped by amines with different hydrocarbon chains such as propylamine, octylamine, dodecylamine and octadecylamine. The introduction of nitrogen atoms and the hydrocarbon chains in the surface of the CQDs dramatically affected their photoluminescence profiles, quantum yields and solubility. The photoluminescence emission wavelength of these novel organic-soluble CQDs depended on the excitation wavelength and their quantum yields varied with the chain length of the hydrocarbon chain attached to the surface of the carbon dots.

In this study, we report on the synthesis of a bioactive glass powder with the original 45S5 composition (Bioglass®) by means of an acetic acid-assisted sol–gel route. A glassy material was obtained after the gels underwent a thermal stabilization treatment at 600 °C for 3 h. Above this temperature, the heat-treated gels crystallized partially, forming a sodium-calcium-silicate Na2CaSi2O6 phase. Even after crystallization, this material showed in vitro bioactivity in simulated body fluid after 12 h, when the formation of hydroxycarbonate apatite on the material surface was identified by X-ray diffraction. Not surprisingly, microbiological assays revealed that these gel-derived materials appear to have an antibacterial effect against Pseudomonas aeruginosa (ATCC 27853)—a Gram-negative bacterium that is noted for its environmental survival versatility, ability to produce biofilm and resistance to some antibiotics. Thus, using common precursors that are widely available, relatively cheap, simple to use, and which result in gels with low stabilization temperature, it was possible to explore the versatility of sol–gel processing to obtain the golden standard 45S5 bioglass.

0 0 1 152 872 UFSJ 7 2 1022 14.0 Normal 0 false false false PT-BR JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Calibri; mso-fareast-language:PT-BR;} Nesse artigo um experimento foi avaliado para explorar e difundir a tematica de energia solar em um contexto interdisciplinar para diferentes cursos de graduacao. Inicialmente o trabalho foi proposto como uma atividade de uma disciplina de pos-graduacao para alunos de mestrado e doutorado. A partir dessa atividade, foi aplicado um experimento envolvendo celulas solares sensibilizadas por corante, avaliada em diferentes cursos de graduacao na forma de minicursos. Celulas solares sensibilizadas por corante foram montadas pelos estudantes, para melhor compreensao sobre a construcao e operacao dessas celulas. Foram desenvolvidas algumas adaptacoes no experimento para o ambiente de sala de aula, facilitando sua execucao, fora de um laboratorio de pesquisa. Os conhecimentos obtidos pelos estudantes foram avaliados a partir de um questionario e seus resultados sao discutidos. A adaptacao de um roteiro experimental envolvendo celulas solares no ambiente de graduacao influenciou positivamente na formacao dos alunos.

Quantum dot-sensitized solar cells (QDSSCs) offer new opportunities to address the clean energy challenge, being one of the top candidates for third generation photovoltaics. Like dye-sensitized solar cells (DSSCs), QDSSCs normally use liquid electrolytes that suffer from issues such as evaporation or leakage. In this study a gel polysulfide electrolyte was prepared containing a natural polymer, agar, and was used as a quasi-solid-state electrolyte in solar cells to replace the conventional liquid electrolytes. This gel electrolyte shows almost the same conductivity as the liquid one. The solar cells were fabricated using CuInS2 quantum dots (QDs), previously synthesized, deposited on TiO2 photoanodes by electrophoretic deposition (EPD). CdS was deposited on TiO2 by successive ionic layer adsorption and reaction (SILAR). Reduced graphene oxide (RGO)–Cu2S, brass, and thin film CuxS were used as counter electrodes. Compared to a liquid polysulfide water based electrolyte, solar cells based on CuInS2 and CdS using gel polymer electrolyte (GPE) exhibit greater incident photon to current conversion efficiency (IPCE = 51.7% at 520 nm and 72.7% at 440 nm), photocurrent density (Jsc = 10.75 and 13.51 mA cm−2), and power conversion efficiency (η = 2.97 and 2.98%) while exhibiting significantly enhanced stability. The solar cells employing the agar-based gel polymeric electrolyte are about a factor of 0.20 more stable than using a liquid electrolyte. The higher photovoltaic performance is due to the good conductivity and high wettability as well as the superior permeation capability of the gel electrolyte into the mesoporous matrix of a TiO2 film.

0 0 1 154 884 UFSJ 7 2 1036 14.0 Normal 0 false false false PT-BR JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Calibri;} Extensivas pesquisas tem sido desenvolvidas com celulas solares (CSs), uma vez que as principais fontes de producao de energia atuais sao derivadas de combustiveis fosseis finitos e que causam problemas ambientais. Nesta perspectiva, o sol pode ser visto como o futuro energetico do planeta, sendo a fonte de energia renovavel mais abundante. O funcionamento basico de uma CS se baseia na habilidade em que os semicondutores apresentam de converter a luz solar em eletricidade, quando expostos a radiacao solar. Um dos semicondutores que tem se destacado em CSs e o dioxido de titânio (TiO 2 ), devido as suas propriedades intrinsecas, como uma larga banda proibida, transparencia a luz visivel, fotoestabilidade, baixo custo, dentre outras. Dentre os principais tipos de CSs que utilizam TiO 2 ­, estao as CSs sensibilizadas por corantes, por pontos quânticos e as de perovsquitas. Nesta revisao os principais aspectos relacionados a sintese, propriedades texturais e morfologicas do TiO 2 de interesse para aplicacao em CSs sao discutidos.

Spectroscopic and structural properties of Er 3+ :Yb 3+ :Tm 3+ triply doped Gd 2 O 3 nanocrystals were investigated. Materiais were heat treated at 800, 900, 1000 and 1100 oC for 4h, and heat treatment effect in the luminescence was discussed. The doping process with RE 3+ was effective on Gd 2 O 3 cubic phase, and structural parameters were determined for this phase. The morphology of the particles did not showed difference on shape and size, demonstrating the reproducibility of the synthesis methods. The luminescence at visible and infrared regions was studied when samples are excited at 980 nm. Materials present intense visible up-conversion and infrared emissions at 1550 nm, and Er 3+ emissions are favored in the materials, concluding that in Er 3+ :Yb 3+ :Tm 3+ triply doped materials the transfer between Yb 3+ and Er 3+ occurs preferentially. Materials due absorption at UV and IR regions can be availed in solar concentrators, as well as 1550nm for optical telecom applications in the C-band.

The modification of endodontic sealers with nanoparticles to confer antimicrobial activity allow greater effect, with interaction at a molecular level. The nanostructured silver vanadate decorated with silver nanoparticles (AgVO3) is a nanomaterial unprecedented in dentistry for this application. This study incorporated the AgVO3 into three endodontic sealers of different compositions and evaluate the cytotoxicity and release of compounds. The groups of commercially available AH Plus, Sealer 26, and Endomethasone N and groups of the same sealers with incorporated AgVO3 (at concentrations 2.5, 5, 10%) were prepared, and extracts of the specimens were obtained for 24 h. The cell viability (cytotoxicity) of human gingival fibroblasts (HGF) was assessed after 24 h, 7 and 14 days. Silver (Ag+) and vanadium (V4+/V5+) ion release was quantified after 24 h by ICP-MS. Data were analyzed by Kruskal–Wallis and Dunn’s post-hoc (α = 0.05). The cell viability was inversely proportional to treatment time. The Sealer 26 and Endomethasone N groups were cytotoxic for HGF cells, regardless of the incorporation of the AgVO3 (p > 0.05), and the incorporation reduced cell viability of AH Plus (p

Made available in DSpace on 2019-10-06T15:29:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-02-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Financiadora de Estudos e Projetos CaTiO3:xEr3+:yYb3+ (x = 0.3mol%; y = 1.0, 1.5 and 2.0 mol%) was synthesized by the sol-gel process. Crystal phase purity, crystallite sizes and microstrain were evaluated as a function of rare earths concentration through XRD and SEM techniques. Upconversion (UC) spectra were recorded at 300 K under excitation at 980 nm and 1550 nm. The samples showed higher intensity of green emission assigned to the upconversion phenomena compared to the red one, when excited at 980 nm and the opposite was observed when excitation was performed at 1550 nm. The nanoparticles CaTiO3:Er3+:Yb3+ were successfully applied as animals cells cytoplasm staining luminescent probes, with low cytotoxic effect being observed. Er3+ emission at 1550 nm was also proposed for in vitro or in vivo optical imaging analysis in the so-called second window (1350–2300 nm). Grupo de Pesquisa em Química de Materiais (GPQM) Departamento de Ciências Naturais Universidade Federal de São João del Rei (UFSJ) Campus Dom Bosco, Praça Dom Helvécio, 74, São João del Rei DeCrtamento de Ciências Naturais Universidade Federal de São João del Rei (UFSJ) Campus Dom Bosco, Praça Dom Helvécio, 74, São João del Rei UNESP Institute of Chemistry, P.O. Box 355 Desenvolvimento de Materiais Inorgânicos com Terras Raras (DeMITeR) Instituto de Química (IQ) Universidade Federal de Uberlândia (UFU), Av. João Naves de Ávila, 212, Uberlândia UNESP Institute of Chemistry, P.O. Box 355 FAPEMIG: CEX - RED-00010-14

One of the major drawbacks in dye-sensitized solar cells (DSSC) is related to the use of a liquid electrolyte, which limits durability and stability. Part of this problem can be solved by replacing the liquid electrolyte by a polymer or gel electrolyte, although the open circuit potential (VOC) of the solar cells is affected. In this work, the role of the reduced graphene oxide (RGO) added to a gel electrolyte in order to improve the efficiency of DSSCs is discussed in detail. The gel polymer electrolyte is composed of poly(ethylene oxide) (PEO), γ-butyrolactone (GBL), LiI, I2, and different concentrations of RGO. The best solar cell using 0.5 wt % of RGO delivered an efficiency of 5.07 ± 0.97%, with the highest values of Isc and VOC. RGO sheets are acting as a multipurpose component in the electrolyte. The recovery of the VOC values can be related to the removal of polyiodide species from the photoanode surface by interaction with the RGO sheets. The increase in the Isc is assigned to the enhancement in ...

The work describes the manufacturing and testing of novel hybrid epoxy/carbon fibre composites with silica micro and poly-diallyldimethylammonium chloride-functionalised nanoparticles. A specific chemical dispersion procedure was applied using the poly-diallyldimethylammonium chloride to avoid clustering of the silica nanoparticles. The influence of the various manufacturing parameters, particles loading, and mechanical properties of the different phases has been investigated with a rigorous Design of Experiment technique based on a full factorial design (2131). Poly-diallyldimethylammonium chloride-functionalised silica nanoparticles were able to provide a homogenous dispersion, with a decrease of the apparent density and enhancement of the mechanical properties in the hybrid carbon fibre composites. Compared to undispersed carbon fibre composite laminates, the use of 2 wt% functionalised nanoparticles permitted to increase the flexural modulus by 47% and the flexural strength by 15%. The hybrid carbon fibre composites showed also an increase of the tensile modulus (9%) and tensile strength (5.6%).

The purpose of this study was evaluate, for the first time, the impact of incorporation of nanostructured silver vanadate (β-AgVO3) in antibiofilm and mechanical properties of dental acrylic resins (poly(methyl methacrylate), PMMA).The β-AgVO3 was synthesized and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and microanalysis (SEM/EDS). Resins specimens were prepared with 0-10% wt.% β-AgVO3 and characterized by SEM, XRD and optical microscopy. The antibiofim activity of the samples against Candida albicans and Streptococcus mutans was investigated by XTT reduction test, colony-forming units (CFUs), and confocal laser scanning microscopy (CLSM). The flexural strength, hardness, and surface roughness of the samples containing β-AgVO3 were compared with the pure PMMA matrix.The incorporation of 10% β-AgVO3 significantly reduced the metabolic activity of C. albicans and S. mutans (p0.05). There was a reduction in microbial load (CFU/mL) of microorganisms for the different concentrations used (p0.05), which was confirmed by confocal microscopy. The addition of β-AgVO3 did not change the mechanical properties of hardness and surface roughness of the resins (p0.05). However, flexural strength decreased with the addition of amounts greater than 1% (p0.05).β-AgVO3 additions in dental acrylic resin may have an impact on inhibition of biofilm of main microorganisms associated with dental prostheses. However, the viability of clinical use should be evaluated in function of changed promoted in some mechanical properties.

This work attempts to obtain Dy3+-doped SiO2–Gd2O3 by sol–gel process, with a molar ratio of 70Si4+–30Gd3+ and Dy3+ concentrations of 0.1, 0.3, 0.5, and 1 mol%. Heat treatment at temperatures of 1000°C, 1100°C, 1200°C, and 1300°C have been performed. From XRD, the Gd2O3 cubic phase was observed at 1000°C and 1100°C, at 1200°C also were observed Gd2O3 monoclinic phase, predominant at 1300°C. The band-gap values vary between 4.4 and 5.3 eV, showing dependence on the crystalline phase. Under UV excitation, emission spectra show bands assigned to the Dy3+ transitions: 4F9/2→6H15/2 (484 nm), 4F9/2→6H13/2 (572 nm), and 4F9/2→6H11/2 (668 nm). The excitation at 275 nm has shown more effective. The ratio between the most intense emission bands (yellow/blue) show values around 0.84 and 1.63. CIE chromaticity diagrams show color coordinates at blue, yellow, and white regions, as a function of Dy3+ concentration and heat treatment. The lifetime values of excited state 4F9/2 were around 0.20 and 0.69 ms. The morphology of particles changed from spherical to coral-like shape as a function of heat treatment are observed. The sol–gel process showed to be an interesting route to obtain Dy3+-doped binary system materials.

This paper presents an evaluation of photoluminescent and structural properties of Eu 3+ -doped TiO 2 materials in powder form prepared by sol–gel process. The increase of heat-treatment temperature of synthesis results in the TiO 2 phase transition, obtaining anatase, rutile and sometimes brookite, examined by Raman and XRD techniques. Crystallite size as well as microstrains in the crystal structure were evaluated as a function of Eu 3+ and heat-treatment temperature. It was found that when Eu 3+ is introduced in anatase phase an intense color emission is observed under excitation at 394 and 463 nm. The rutile phase presents inversion center symmetry, and apparently the Eu 3+ tends to occupy this site, which decreases the intensity of the emission assigned to the 5 D 0 → 7 F 2 transition. The materials obtained at 700 °C showed most intensity of emission in the red region, verified by the ratio between 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 transitions of Eu 3+ . The results showed that the materials are interesting absorber in the ultraviolet and red region and can be used for improvement of energy conversion in solar cells devices.