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Phosphor materials with narrow emission bands and high quantum efficiency have received a good amount of attention, suggesting the possibility of several applications in the field of optoelectronic devices. SrTiO 3 :Pr is an example of a material with these characteristics. In this study, mesocrystal samples of Sr 0.998 Pr 0.002 Ti 1−y Al y O 3 (SrTiO 3 :Pr,Al) were prepared via a hydrothermal route, and the morphology presented a microcube shape and pristine structure with Pm3m space group without any spurious phases for all Al concentrations. Measurements of X-ray absorption spectroscopy (XAS) at Ti K-, L II , III -, and O K-edges, calculated projected density of states, and Raman spectroscopy revealed that the hydrothermal method and Al incorporation cause a local symmetry breaking, deviating from the cubic structure, Ti off-center displacement, tilting of TiO 6 octahedra, and O vacancies. As the Al content increases, the intensity of some emissions in the photoluminescence spectra also increases up to 3 at%. The disorder produced by Al concentration leads to a lower symmetry around Pr3+ sites, resulting in an increase in the probabilities of transitions for Pr3+ ions due to the mixing of the opposite parity in 4 f configurational levels. On the other hand, higher Al concentrations cause a decrease in the intensity of Pr emissions, which is related to their quenching because of O vacancies. Additionally, intrinsic defects due to the hydrothermal route and Al incorporation generate a broad emission in the photoluminescence spectra. This broad emission is associated with intermediary electronic levels in the band gap caused by these intrinsic defects. • Sr 0.998 Pr 0.002 Ti 1−y Al y O 3 phosphor mesocrystals were prepared via hydrothermal route. • The morphology presents microcube shape of the mesocrystals without spurious phases. • X-ray absorption spectroscopy detected local disorder and O vacancies. • Lower symmetry around Pr3+ increases the probabilities of the 4f transitions. • Intrinsic defects generate a broad emission in photoluminescence spectra. [ABSTRACT FROM AUTHOR]

Abstract The biofilm accumulation over the composite resin restorations can contribute to the formation of secondary caries. In this way, antibacterial restorative composite resins are highly desired. Then, the purpose of this study was to modify a composite resins using Ag doped ZnO nanoparticles (NPs), evaluate the antibacterial and mechanical properties of the modified composite resin. The ZnO/AgNPs were synthesized by two different routes, polymeric precursor and coprecipitation methods, and characterized by thermal decomposition, X-ray diffraction, specific surface area by N 2 desorption/desorption and scanning electron microscopy (SEM). Antibacterial activity of composite resin specimens (4 mm in height and 2 mm in diameter; n = 15) modified by ZnO/Ag nanoparticles was performed against 7-days Streptococcus mutans biofilm. Colony forming units (CFU/mL) were used to evaluate the bacterial activity. Additionally, the morphology and the bacteria adherence area were analyzed by SEM images. Cylindrical specimens (6 mm in height and 4 mm in diameter; n = 20) of the composite resin containing ZnO/Ag NPs were prepared to perform compressive strength in a universal mechanical test machine, and the surface of fractured specimens was analyzed by EDX element mapping to verify NPs homogeneity. The normal distribution was confirmed and the two-way analysis of variance (ANOVA) and Tukey's test for pair comparison were performed. The nanospheres of ZnO/Ag lead to a better biofilm inhibition, than nanoplates. No difference on compressive strength was found for the composite resin modified by ZnO/Ag nanoplates. Based on these results, this material could be a good option as a new restorative material. Highlights • ZnO micro and nanoparticles with antimicrobial properties were satisfactorily synthetized by the different routes. • The composite resin containing ZnO particles significantly inhibit the S. mutans biofilm. • The compressive strength of the composite resin containing Ag/ZnO nanoplates did not drastically changed. [ABSTRACT FROM AUTHOR]

Highlights • The modification of the composite resin using pure and Ag decorated TiO 2 can decrease S. mutans biofilm formation over the composite resin surface. • The properties of the modified composite resin did not change after the modification with TiO 2 /Ag (PREC POL). • The TiO 2 /Ag nanospheres obtained by polymeric precursor synthesis seems to be the best nanomaterial. Abstract Objective The aim of this study was to evaluate the antibacterial activity of a composite resin modified by TiO 2 and TiO 2 /Ag nanoparticles and their influence over different properties. Methods TiO 2 and TiO 2 /Ag NPs were synthesized by polymeric precursor and microwave-assisted hydrothermal methods and then, characterized by different techniques. Direct contact test was performed using Filtek™ Z350XT blended with 0.5; 1 and 2% (wt.) of NPs against Streptococcus mutans to determine the best concentration to the other tests. After that, the modified composite resin was tested against S. mutans 7-day biofilm (CFU/mL). Also, compressive and diametral tensile strength (n = 40), degree of conversion (n = 25) and surface roughness (n = 50) was performed. The data were analyzed by ANOVA and Tukey's test for multiple comparison at 5% significance level. Results The direct contact test demonstrates that by increasing the nanoparticle content, the bacterial growth is significantly reduceed (p < 0.05). The inclusion of 2% of TiO 2 /Ag NPs significantly decreased (p < 0.05) the biofilm accumulation of S. mutans on the composite resin surface compared to the control Group. The TiO 2 NPs treated with an organosilane increased compressive strength of composite resin (p < 0.05). Degree of conversion remained unchanged (p > 0.05) and the surface roughness increased with the NPs (p < 0.05), except for the TiO 2 by polymeric precursor Group (p > 0.05). Significance The development of an antibacterial dental restorative material that hinder S. mutans biofilm without sacrificing the mechanical and physical properties is desirable in dental material science. [ABSTRACT FROM AUTHOR]

Abstract Pr3+-doped perovskite-based SrTiO 3 phosphors have been developed as a potential red phosphor. In this paper, we report the substitution of La3+ ions for Sr2+ ions in order to promote Sr vacancies to further enhance photoluminescence. Given that the La content increases, an enhancement in the intensity of all emissions is observed, mainly for 1D 2 –3H 4 and 3P 0 –3H 6 transitions. This enhancement of photoluminescence emissions is associated with disorder in the lattice caused by La incorporation. Raman measurements and X-ray absorption near edge structure (XANES) spectra at the Ti K-edge identify this disorder as a function of the La content. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Zinc sulfide (ZnS) pure or doped has received remarkable attention because of fundamental properties, versatility and potential for several technological applications as luminescent material. In this study, the local structure and photoluminescence properties of nanostructured Zn1-xMnxS samples have been characterized. X-ray diffraction results show that ZnS:Mn samples crystallized completely without the presence of secondary phases and the diffraction patterns correspond to the cubic zinc blende. Theoretical and experimental XANES (X-ray absorption near edge structure) spectra at Zn K-edge suggest the incorporation of Mn atoms into the ZnS host and indicate the occurrence of Zn and S vacancies, which are confirmed by EXAFS (extended X-ray absorption fine structure) fit results. These vacancies can be related to a red-shift observed in the peak emission of photoluminescence spectrum for ZnS sample, which is centered at ∼ 504 nm. As the Mn content increases, a yellow-orange emission centered at ∼ 590 nm can be observed besides the blue-green emission, which is associated with the 4T1-6A1 transition within the 3 d shell of Mn2+. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study of the influence of particle size on the structural and dielectric properties of Pb0.85La0.15TiO3 (PLT15) ferroelectric ceramic samples. The samples were prepared with average grain size of 1.69±0.08μm and 146±8nm using, respectively, conventional and spark plasma sintering techniques. A decrease in the tetragonality degree as the crystallite size decreased was explained by an internal stress caused by the existence of a large amount of grain boundaries. The local structure exhibited no significant modification and the dielectric measurements showed a diffuse phase transition and a reduction in the permittivity magnitude at T m as the average grain size decreased. The nanostructured ceramic sample prepared at a relatively lower temperature and sintering time presented a dielectric constant value of approximately 2000 at room temperature. [Copyright &y& Elsevier]

The development of stable and reproducible inorganic pigments is noteworthy for industrial applications mainly considering more intense shades and low toxicity. Among the various candidates to substitute non‐hazardous red and yellow pigments, CeO2 and CeO2:Pr have been attracting attention because of their opacity and high‐temperature stability besides being environmental‐friendly and health‐friendly. In this study, nanostructured CeO2 and CeO2:Pr samples were synthesized using the polymeric precursor method and structural and optical characterizations were performed. Scanning electron microscopy reveals the morphology of CeO2 nanoparticles in which the particle size ranges from 22 to 28 nm as a function of the annealing temperature. Pr‐doping does not show influence on the particle size. XRD results show that CeO2 and CeO2:Pr samples crystallize in the cubic fluorite lattice with Fm3m space group. Raman spectra show the fluorite F2g mode, confirming the XRD results. With Pr‐doping and the annealing of the samples, two bands are observed between 550 and 600 cm−1, which are related to the defects in the fluorite structure associated with oxygen vacancies. XPS spectra reveal an increase in the ratio of Ce3+ ions depending on the annealing temperature and Pr‐doping. This increase is associated with the carbon removal from the lattice by annealing. This behavior causes a change in the hue of the powders as the annealing temperature increases. According to diffuse reflectance and colorimetric measurements, CeO2 shows a light‐yellow color due to the O 2p-Ce 4f transitions whose b* parameter mainly decreases with annealing, becoming almost white. The CeO2:Pr sample exhibits a red‐orange color because of the electronic transitions between 4f2 → 5d1 states of Pr3+. Upon annealing, L* and b* parameters decrease, resulting in a red‐brown shade. The charge compensation or charge transfer is responsible for the modification of the hue of these pigments. [ABSTRACT FROM AUTHOR]

Abstract Zinc sulfide (ZnS) is a II–VI inorganic semiconductor material and has received remarkable attention because of fundamental physical properties, versatility, nontoxicity, chemical stability and has been widely applied to make numerous optical devices as phosphor material. As a wide band gap semiconductor, ZnS can easily host different metal ions as luminescent center to improve or modify its structural and optical performances such as Cu atoms. In this paper, ZnS:Cu nanoparticles were synthesized by solvothermal method and the photoluminescence and the structural at long- and local-range properties were characterized. According to X-ray diffraction results, ZnS sample crystallizes with the cubic zinc blende structure (F- 43 m space group) without spurious phases. Images from transmission electron microscope depict the morphology of ZnS particles as round shape and average size value lower than 5 nm. Theoretical and experimental X-ray absorption near edge structure (XANES) spectra at Zn K-edge suggest the incorporation of Cu atoms into the ZnS host and indicate the occurrence of Zn and S vacancies, which are confirmed by extended X-ray absorption fine structure (EXAFS) fit results. These native defects are related to a red-shift observed in the peak emission of photoluminescence (PL) spectrum for ZnS sample, which is centered at ~ 504 nm. An emission in orange-red region is observed as Cu is incorporated in the ZnS host matrix that is attributed to the transition from the 4T 1 level to the 6A 1 level. Moreover, the intensity of the emissions due to zinc vacancies and interstitial zinc in the deconvoluted PL spectrum is in accordance with results determined in X-ray absorption spectroscopy characterization. [ABSTRACT FROM AUTHOR]

Ceramic pigments based on chromium-doped yttrium aluminate (YAl 1-X Cr X O 3 ; x = 0.01; 0.03 and 0.05 mol%) were obtained by using chemical combustion method. Chemical processes with and without the use of mineralizers were employed. The modifications in the structure, morphology, optical and thermal properties caused by the inserted agents in the aluminate network were investigated by means of the following techniques: X-ray diffraction (XRD), Rietveld refinement, diffuse reflectance spectroscopy in the ultraviolet–visible region (UV–Vis), Fourier-transform infrared (FTIR) spectroscopy, field emission gun scanning electron microscopy (FEG-SEM), and CIELab colorimetric coordinates. The pigments were applied to ceramic pieces and the color stability was evaluated. XRD patterns results coupled with Rietveld refinement analyses showed a pronounced phase evolution for the samples containing mineralizers. This confirmed the effectiveness of these constituents for the formation of yttrium aluminate perovskite phase. The UV–Vis spectra showed greater reflectance in samples without mineralizers, while FTIR spectroscopy Analysis showed bands of vibration related to Al3+ coordinated octahedrally for both systems. Samples with the presence of mineralizer agents showed morphology similar to a cube with the presence of primary aggregated particles as revealed by FEG-SEM. The colorimetric pigments data showed values of the a* coordinate, which is related to red color components. This value was higher for the powder in the system with mineralizers as well as in the pigments that were employed on the ceramic pieces. [ABSTRACT FROM AUTHOR]

The complete comprehension of the magnetic properties of the dilute magnetic oxides has emerged as one of the major challenges in the fields of materials science and condensed matter physics. Up to now, there is no consensus about the mechanism behind the so often observed room temperature ferromagnetism. However it is well known that defects plays an important role in the context. Here we present the study of the correlation between the structural and the magnetic properties of nanoparticulate Co-doped ZnO (Zn 1− x Co x O, x = 0.02 and 0.08) thin films prepared via Electron Beam-Physical Vapor Deposition. The structural results confirms the incorporation of the Co 2+ ions into the ZnO host matrix with no secondary phases. Magnetic measurements show a robust ferromagnetic order for the thin film with x = 0.08, whereas for the sample with x = 0.02 only a tiny ferromagnetism were observed. We could explain the differences in the magnetic behavior entirely under the scope of the spin-split impurity band model. In this work we also present convincing evidences of the no correlation between the oxygen vacancies and the desired room temperature ferromagnetism. [ABSTRACT FROM AUTHOR]

Objective. The aim of this study was to evaluate the physicochemical properties and bioactivity of two formulations of calcium silicate-based cements containing additives (CSCM) or resin (CSCR), associated with radiopacifying agents zirconiumoxide (ZrO2) and niobium oxide (Nb2O5) as micro- and nanoparticles; calcium tungstate (CaWO4); and bismuth oxide (Bi2O3). MTA Angelus was used as control. Methods. Surface features and bioactivity were evaluated by scanning electron microscopy and the chemical composition by energy dispersive X-ray spectrometry (EDS-X). Results. CSCM and CSCR presented larger particle sizes thanMTA. Hydroxyapatite deposits were found on the surface of some materials, especially when associated with the radiopacifier with ZrO2 nanoparticles. All the cements presented calcium, silicon, and aluminum in their composition. Conclusion. Both calcium silicatebased cements presented composition and bioactivity similar to MTA when associated with the radiopacifiers evaluated. [ABSTRACT FROM AUTHOR]