Search

Er and Er,Yb-activated zinc-tin-oxide-based phosphors are synthesized for the first time by a mechanochemical solid-state method. Several techniques, including X-ray diffraction (XRD), Raman, and photoluminescence (PL) spectroscopy are used for structure and optical investigation. Morphology analysis by scanning electron microscopy (SEM) shows agglomerates of non-uniform in size and shape particles. XRD analysis confirms the major inverse spinel Zn2SnO4 phase formation with high crystallinity. Luminescence activation by Er3+ upon 980 nm excitation leads to green emissions centered at 532 nm and 551 nm and a narrow-band red emission centered at 654 nm that double increases by Yb3+ ions cooperative sensitization.

The aim of this study was to improve the mechanical properties and to optimize antimicrobial activity of hydroxyapatite (HAP) by simultaneous doping with Mg and Cu ions in order to obtain material that would be able to assist in the bone/tooth healing process, prevent post-implementation infections and provide satisfying values of hardness and fracture toughness for biomedical application. Ion doping was done during the hydrothermal synthesis of HAP powders, whereby the content of Mg ions in the starting solution was varied between 1-20 mol. % with regard to Ca ions, while the amount of Cu ions was kept constant at 0.4 mol. %. The green compacts were sintered for 2 h at temperatures ranging 750–1200 °C depending on the Mg content, chosen in agreement with dilatometry results. Presence of Mg ions was found to favour transition from HAP to β−tricalcium phosphate phase (β−TCP), which enabled formation of biphasic HAP/β−TCP and pure β−TCP phase at 160 °C during hydrothermal synthesis. In vitro investigation of antimicrobial activity against Escherichia coli, Staphylococcus aureus and Enterococcus faecalis showed satisfactory antimicrobial activity. MTT assay performed on MRC-5 and L929 cell lines showed excellent cytocompatibility and cell proliferation. Maximum hardness by Vickers and fracture toughness values, 4.96 GPa and 1.75 MPa m1/2 respectively, were obtained upon addition of 5 mol. % Mg, as a consequence of the lowest grain size and porosity, as well as the highest densification rate. This is, to the best of our knowledge, the highest fracture toughness for HAP or β-TCP ceramics reported thus far. Published version: [http://technorep.tmf.bg.ac.rs/handle/123456789/4126] This is the peer-reviewed version of the following article: Veljović Đ, Matić T, Stamenić T, Kojić V, Dimitrijević-Branković S, Lukić MJ, Jevtić S, Radovanović Ž, Petrović R, Janaćković Đ. Mg/Cu co-substituted hydroxyapatite - Biocompatibility, mechanical properties and antimicrobial activity. in Ceramics International. 2019;45(17):22029-22039. [https://doi.org/10.1016/j.ceramint.2019.07.219]

© 2018 Elsevier Ltd and Techna Group S.r.l. This paper describes the processing, microstructure, optical and electrical properties of the nanocrystalline (NC) niobium and zinc doped titanium-tin-oxide (TTO:NZ) based ceramics. Variety of techniques was employed (X-ray diffraction, scanning electron microscopy, energy dispersive, Raman and impedance spectroscopy) in the characterization of the obtained TTO:NZ, which confirmed the formation of NC solid-solution matrix with Ti0.8Sn0.2O2 composition. A specific highly dense (approximately 97% of the theoretical density was reached) varistor like microstructure (matrix metal-oxide grains surrounded by the grain-boundary regions) and accordingly resembling electrical properties (breakdown electric field of approximately 130 V/mm and nonlinearity coefficient of α ≈ 6.5) were achieved through double cation doping and elected condition of the mechanochemical solid-state synthesis. Impedance response analysis of TTO:NZ ceramics by means of an equivalent electrical circuit based on the brick-layer model for polycrystalline materials revealed the presence of two temperature dependent electrical relaxation phenomena of the non-Debye type as well as the negative temperature coefficient of resistance behavior.

This paper reports on novel cobalt oxide nanoparticles (NPs) embedded in an amorphous silica (SiO2) matrix, synthesized using a modified sol-gel method. SEM and TEM images show as-synthesized particles to aggregate in the shape of spheres and less than 5 nm in size, while XRD and SAED analysis both point to well crystallized cubic spinel cobalt oxide phase with an average crystallite size of about 4.6 nm. Raman analysis confirms the formation of cobalt (III) oxide (Co3O4) NPs. As-synthesized Co3O4 single-nanocrystallite has magnetic properties that correlate with finite size effects and uncompensated surface spins. Temperature dependence of ZFC-FC magnetization curves reveals a sharp peak around 10 K which corresponds to the blocking temperature. A Curie-Weiss behavior of magnetization above 25 K shows lower Neel temperature of the sample compared with its bulk counterpart T-N=40 K (possibly due to crystal defects and nano-dimensionality of the particles). The magnetic measurements exhibit high magnetization at low temperatures (M-s=54.3 emu/g) which can be associated with random canting of the particles surface spins and uncompensated spins in the core which tends to interact ferromagnetically at low temperatures. The initial magnetization curve falls out from the hysteresis loop at 5 K, which could be also the effect of surface spins. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Heterojunction zinc tin oxide (ZnO/SnO2) nanoparticles were prepared using a top–down traditional solid-state method; mechanical grinding followed by annealing, and characterized by X-ray diffraction, multi-wavelength excitation Raman scattering, scanning electron microscopy, diffuse reflectance and photoluminescence spectroscopy. The photocatalytic degradation kinetics of amitriptyline in the presence of the obtained ZnO/SnO2 nanoparticles under simulated solar and UVA irradiation was determined and used as a model reaction for understanding the photocatalytic mechanism when such mixed oxide semiconductors are used in removing the pharmaceutically active compounds from wastewaters.

Nanostructured calcium phosphate functionally graded materials (FGMs) with simultaneous gradients of density, phase composition, and mechanical properties were fabricated by consecutive uniaxial pressing of stoichiometric (SHAp) and calcium deficient (CDHAp) hydroxyapatite powders in multilayered samples and reaction sintering. During sintering procedure SHAp composition remained stable (HAp) while CDHAp was phase transformed in biphasic calcium phosphate (BCP, i.e. HAp+β-TCP) yielding HAp/BCP FGMs. To reduce mismatch stress between adjacent layers, generated during sintering, gradient of phase composition was optimized by introducing intermediate layer(s) made from mixture of SHAp and CDHAp in appropriate mass ratio. Optimal processing conditions for preparation of nanostructured ceramics were provided via two-step sintering. High-quality FGMs structure, without delamination, cracks and micro-structural damages was observed by SEM technique; moreover, a detailed examination by FE−SEM established the unidirectional (perpendicular with respect to the layers) gradual change of microstructure, from fully dense to ~40% of porosity. Detailed micro-Raman and FTIR spectroscopy studies showed increase of β-TCP amount along the FGMs height, confirming gradient of phase composition. Mechanical properties measured by microindentation revealed gradual change of microhardness from 650 to 115 HV, with simultaneous change of Young's modulus from 92 to 24 GPa. This is the peer‐reviewed version of the paper Marković, S., Lukić, M.J., Škapin, S.D., Stojanović, B., Uskoković, D., 2015. Designing, fabrication and characterization of nanostructured functionally graded HAp/BCP ceramics. Ceramics International 41, 2654–2667. [https://doi.org/10.1016/j.ceramint.2014.10.079]

In this research we prepared nanocrystalline YNbO4:Eu3+ phosphor, i.e. nanophosphor, powder using an efficient mechanochemical method followed by annealing. X-ray diffraction analysis revealed that YNbO4:Eu3+ crystallizes in monoclinic structure C2/c where, from the point of view of A and B in ABO(4) compounds, cation coordination can be noted as [6+2, 4+2]. Crystallite size of about 40 nm, was estimated using Debye Scherrers equation. Raman spectroscopy with 785 and 532 rim excitation wavelengths is performed to record a majority of materials phonon modes and to provide more in depth understanding of the YNbO4 structure. Scanning electron microscopy observations indicate that the mechanical treatment during synthesis is causing non-uniformity of the powder microstructure. High resolution photoluminescent measurements upon UV excitation showed intense emission coming from f-f transitions of the europium ion with the lifetime of 0.68 ms, suggesting that the obtained YNbO4:Eu3+ is a good potential phosphor. A comparison of emissive properties with microcrystalline YNbO4:Eu3+ was made and it showed higher values of emission intensity and lifetime of the nanocrystalline sample.(C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Mg-doped ZnO nanocrystallites were prepared via conventional solid-state reaction when ZnO and MgO precursors were stoichiometrically mixed and heated at 700 °C, 900 °C and 1100 °C for 2 h in air atmosphere. Influence of annealing temperature on structural and optical properties of the obtained nanoparticles was investigated using X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, Raman and UV–vis spectroscopy. The efficiency of Mg-doped ZnO water suspensions in the photocatalytic degradation of alprazolam, short-acting anxiolytic of the benzodiazepine class of psychoactive drugs, under UV irradiation was compared with efficiency of pure ZnO and TiO 2 Degussa P25.