Vinča Institute of Nuclear Sciences

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    First-principles calculations of the electronic structure and mechanical properties of non-doped and Cr3+-Doped K2LiAlF6 under pressure

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    We report on the results of the first principles calculations based on density functional theory (DFT) of the electronic structure and mechanical properties of K2LiAlF6, both non-doped and doped with Cr3+ ions. The densities of states of K2LiAlF6 and the K2LiAlF6:Cr3+ phosphor as well as the crystal-field strength 10Dq, the Cr3+ 2E→4A2 emission energy, elastic constants, bulk and shear moduli, sound velocities and Debye temperature as functions of hydrostatic pressure ranging from 0 up to 40 GPa were calculated. The present DFT calculations indicate that, the band gap of non-doped K2LiAlF6 increases quadratically with increasing pressure. Further, the crystal field strength 10Dq and the 2E→4A2 emission energy, the Debye temperature, sound velocities and shear moduli of Cr-doped K2LiAlF6 increase with increasing pressure, while the 2E→4A2 emission energy becomes red-shifted, which indicates potential applicability of the studied system for pressure sensing. Such calculations for the title system were performed for the first time; the obtained results provide a firm basis for a deeper understanding of physical properties of both neat and doped functional materials

    Tuning phase and photoluminescent properties of ZrO2:Eu3+ coatings formed by plasma electrolytic oxidation and Judd-Ofelt analysis of composite materials

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    Eu3+ doped Zirconia coatings were synthesized by the electrochemical plasma electrolytic oxidation method in only 8 min from the pure zirconium substrate. The phase constitution from pure monoclinic to pure tetragonal and exactly in between was achieved by using different concentrations of Na3PO4 and NaAlO2 electrolytes. The complex emission spectra composed of Eu2+, Eu3+, and ZrO2 defect emission greatly depend on the excitation wavelength and phase constitution. Eu3+ photoluminescence properties depend on the phase, which is reflected by the different Stark splitting and different intensities of transitions. Thus, both phase and photoluminescent properties of ZrO2 coatings are fine-tuneable. Judd-Ofelt analysis was performed from the emission and excitation spectra, showing that all 3 intensity parameters depend linearly on the phase constitution, being largest in the pure monoclinic phase. The mixed phase has Judd-Ofelt parameters between those in pure phases. Eu3+ has 2.45 times more preference to get incorporated into the tetragonal than in the monoclinic phase in the mixed phase samples. The general equation for Judd-Ofelt parameters in a compound with mixed constituents and probability of incorporation is introduced, allowing also for a prediction of the spectrum shape based on the Judd-Ofelt parameters of pure-phase compounds. Python software code for estimating the percent of incorporation by multiple linear regression model is also provided

    Dental material based on poly(methyl methacrylate) with magnesium-aluminum layered double hydroxide (MgAl-LDH) on bio-silica particles

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    The MgAl-LDH@SiO2 particles are prepared by the coprecipitation of LDH on silica originating from plants.Particles are of submicron size and are well dispersed in the matrix. Composites consisting of PMMA reinforcedwith MgAl-LDH@SiO2 particles have improved hardness and resistance to viscoelastic deformation, as tested bymicrohardness measurements

    Employing carbon quantum dots to combat cytomegalovirus

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    Carbon quantum dots (CQDs) are well known as a promising therapeutic agent due to their excellent pro-oxidant, antioxidant, antibacterial and anticancer properties under visible light irradiation. This material is easy to produce by several bottom-up or top-down methods. In this study, we used citric acid as starting precursor to synthesize aqueous carbon quantum dots dispersion by pyrolysis at 210 ◦C. Atomic force microscopy and XPS analyses revealed that CQDs synthesized are quasi-spherical with typical diameter of 9 nm and lots of C–O and C––O functional groups distributed over the basal plane and edges of the dots. Here, we investigated the antiviral properties of CQDs against cytomegalovirus (CMV). The pre-treatment with CQDs upregulates interferonstimulated genes (ISG), resulting in better virus control. Cellular defence against cytomegalovirus of CQDs pre-treated cells is increased in a dose-dependent manner. Our results reveal high biocompatibility and potent in vitro antiviral properties of CQDs

    Potential of applying the quadratic failure criteria for short carbon fibre-reinforced PET-G composite material used in additive manufacturing

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    Short carbon fibres (SCF) have been introduced in additive manufacturing (AM) of polymer-based parts designed for moderate loadings. Alongside other influential parameters for the strength and stiffness of thus obtained composite materials, scientific papers in AM field emphasize the effect of raster angle (printing direction) applied. Consequently, this study considers the idea of comparing the yield strength values experimentally evaluated for plate specimens additively manufactured from SCF-reinforced PET-G filament applying different raster angles with theoretical tensile strength vs fibre orientation curves already known from Classical Lamination Theory (CLT) for continuous fibre-reinforced composite laminas. Among many failure criteria relevant to ductile isotropic materials, maximum distortional energy criterion (von Mises) is the most widely used. Thus, von Mises criterion is usually used for predicting the onset of yielding in isotropic metals. However, for anisotropic composite materials, such as thin plates made from continuous fibre-reinforced polymers, the use of von Mises failure criterion is not applicable. Therefore, quadratic interaction criteria (e.g. Tsai-Hill) are often proposed for such materials. In this study, Tsai-Hill quadratic interaction criterion is implemented in order to predict the onset of yielding (failure) of thin composite plates made from SCF-reinforced PET-G. The off-axis tensile test is used to experimentally evaluate the failure of test samples printed with different raster angles. Linear-elastic material behaviour model was determined by modulus of elasticity and the value of yield strength for each sample set (seven sets were observed, raster angle ranging from 0° to 90° with the increment of 15°). Obtained results suggest that Tsai-Hill quadratic interaction criterion can be considered as a potential candidate for criterion capable to predict the onset of yielding (failure) of thin composite plates additively manufactured from SCF-reinforced PET-G material

    Nanoscale metal oxides as materials used for modification of carbon-based electrodes in electrochemical sensors

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    Nanostructured metal oxides used as modifiers of various carbon-based working electrodes serve as the basis for designing sensitive electrochemical sensors to detect desired analytes. The sensors we develop are distinguished by low detection limit (LOD), high analyte selectivity, sensitivity, and versatile real-world sample use case. In this work we present the design of two based on metal oxides as modifiers of carbon paste working electrode (CPE) and their applications in the electrochemical determination of levodopa and adrenaline. The physicochemical properties of designed materials were analyzed by complementary experimental technics (XRPD, TEM, SEM, EDS, electrochemical measurements) to determine their (micro)structural properties and correlate them with electroanalytical performance. Europium has been considered a significant lanthanide element with higher redox reaction behavior. We conducted a hydrothermal synthesis of Eu2O3@Cr2O3 and used them for CPE modification. The proposed Eu2O3@Cr2O3/CPE electrode was used to develop an analytical procedure quantifying L-Dopa in a wide micromolar linear range (1-100 µM), high sensitivity of 1.38 µA µM−1 cm−2 and a low detection limit (LOD = 0.72 µM). On the other side, we investigated the physicochemical properties of the gallium/bismuth mixed oxides and studied the influence of different Ga2O3:Bi2O3 ratios on the electrochemical detection of adrenaline. Square wave voltammetry was optimized, and the best electrode showed a wide linear working range of 7-100 μM, under optimized conditions. The LOD for the proposed sensor was calculated to be 1.9 μM, with a low limit of quantification (LOQ = 5.8 μM). The total performance of the sensors, particularly their performance on real-world samples and their potential for commercialization, had to be carefully evaluated during the sensor construction. Our team is devoted to developing highly selective electrochemical sensors based on nanomaterials to be potentially used as the basis for the fabrication of high-performance miniature devices with exceptional sensitivity to specific analytes, like adrenaline and L-Dopa, in this research

    Amorphous non-doped and Se-, Cu-, and Zn-doped Sb2S3 nanoparticles prepared by a hot-injection method: bandgap tuning and possible observation of the quantum size effect

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    Amorphous, non-doped, and copper- and selenium-doped Sb2S3 nanoparticles were synthesized by a hot-injection method. Zinc-doped Sb2S3 nanoparticles were prepared for the first time using the same approach. Electron microscopy revealed that spherical nanoparticles of 1–4 nanometers aggregated into larger spherical clusters. Introducing dopants into the Sb2S3 structure neither influenced the samples’ spherical morphology nor their sizes. The presence of the dopants (Cu, Se, or Zn) was confirmed by energy dispersive X-ray (EDX) and, in the case of Zn, also by inductively coupled plasma-mass spectrometry (ICP-MS). The X-ray powder diffraction (XRPD) patterns of the non-doped and doped samples imply an amorphous structure. Crystalline Zn-doped Sb2S3 revealed defined peaks from only the Sb2S3 phase, indicating successful doping. Diffuse reflectance spectroscopy (DRS) revealed high optical bandgap energies (2.03–2.12 eV) compared to the values (1.6–1.7 eV) for large non-doped and doped particles obtained at 240 °C, which might be attributed to a quantum size effect. X-ray photoelectron spectroscopy (XPS) revealed a phase without any impurities for the undoped and characteristic peaks for copper, selenium, and zinc Auger for the doped samples. XPS valence band confirm for the Zn-doped particles a shift towards lower binding energy compared to the non-doped samples, indicating successful doping. Photoluminescence (PL) measurements show that embedding Zn into the Sb2S3 host lattice suppresses the wide luminescence band related to intrinsic vacancy defects. Narrow peaks at 1.7–2.4 eV were found to be associated with singlet excitons. The energy dependence of the light emission on the synthesized nanoparticles’ size suggests quantum confinement. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.Preprint version available at: [https://doi.org/10.21203/rs.3.rs-1945841/v1

    Mg substituted hydroxyapatite for application in bone tissue engineering

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    VII Conference of The Serbian Society for Ceramic Materials, 7CSCS-2023, June 14-16, 2023, Belgrade, Serbi

    Helical and square-spiral copper nanostructures: The effect of thickness and deposition conditions on the structural and optical properties

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    We have investigated the effect of thickness and deposition conditions on the structural and optical properties of nanostructured copper (Cu) thin films, deposited using e-beam glancing angle deposition. In the first series of experiments, samples were deposited in the form of helical nanostructures, to the thicknesses of 160 nm, 280 nm, 450 nm and 780 nm. The second set of the samples was fabricated in the form of zigzag and square-spiral nanostructures to a thickness of approximately 300 nm, by using different azimuthal rotations (φ = 180o, 90o, 45o, 22.5o and 11o). Field-emission scanning electron microscopy and high-resolution transmission electron microscopy were utilized to explore morphological and structural properties, while optical studies were done using spectroscopic ellipsometry. The results showed that for both series of the samples the deposited structures are porous with nanometer-sized particles. Detailed analyses of optical properties revealed that the thickness of the films had a significant impact on the dielectric function of Cu structures. With increasing the thickness from 160 nm to 780 nm the surface plasmon resonance (SPR) peak was shifted from 1.31 eV to 1.05 eV. Changes in SPR peak position were associated with the growth mechanism and the size of deposited nanostructures. For the second series of the samples, it was found that as the azimuthal rotation decreases, deposited nanostructures become more porous with larger number of grown arms. Optical analysis showed that the properties of the grown Cu films are greatly influenced by the deposition conditions. By decreasing the φ parameter, SPR peak was shifted from 1.19 eV to 0.75 eV, which can be correlated with the size distribution and agglomeration of Cu nanoparticles.IX International School and Conference on Photonics : PHOTONICA2023 : book of abstracts; August 28 - September 1, 2023; Belgrad

    Rosette based metamaterial for circularly polarized terahertz waves manipulation

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    Metamaterials that respond resonantly in interaction with the terahertz (THz) electromagnetic waves are significant for the achievement of diverse optical functionalities in THz spectral range [1]. Also, they are virtually desirable platforms for investigating chiral effects which rise due to different interaction of metamaterials with left and right circularly polarized light [2,3]. Light polarization is an important feature of electromagnetic waves and manipulation of polarization plays pivotal role in various areas such as communications, imaging and sensing. One of potential applications of the THz metadevices is for protein quality control in the biotechnology or food industries [4]. Chiral properties of metamaterial can be modified via different external influences, such as by changing the interlayer twist angle, adding a dielectric spacer, or modulating its thickness. Twisting or rotating achiral layered structures in parallel planes enables engineering of the extrinsic chirality and consequential optical performance. For example, the twist angle from counterclockwise rotation of an upper layer with respect to the one under it, leads to a left-handed stacking geometry [5]. In this study, we performed numerical simulations of the metamaterial structure in terahertz frequency range, 0.25-0.75 THz. The numerical simulations were done for the case of two parallel gold rosettes on sapphire substrates in which we analyzed the influence of rotating one rosette with respect to the another on chiral properties. Two geometries of the rosette based structures were studied. First geometry is based on resonator which consists of two same parallel rosettes and the second one of two parallel rosettes, but one of them is trimmed.IX International School and Conference on Photonics : PHOTONICA2023 : book of abstracts; August 28 - September 1, 2023; Belgrad

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