Preparation of Barium-Hexaferrite/Gold Janus Nanoplatelets Using the Pickering Emulsion Method

Janus particles, which have two surfaces exhibiting different properties, are promising candidates for various applications. For example, magneto-optic Janus particles could be used for in-vivo cancer imaging, drug delivery, and photothermal therapy. The preparation of such materials on a relatively large scale is challenging, especially if the Janus structure consists of a hard magnetic material like barium hexaferrite nanoplatelets. The focus of this study was to adopt the known Pickering emulsion, i.e., Granick’s method, for the preparation of barium-hexaferrite/gold Janus nanoplatelets. The wax-in-water Pickering emulsions were stabilized with a combination of cetyltrimethyl ammonium bromide and barium hexaferrite nanoplatelets at 80 °C. Colloidosomes of solidified wax covered with the barium hexaferrite nanoplatelets formed after cooling the Pickering emulsions to room temperature. The formation and microstructure of the colloidosomes were thoroughly studied by optical and scanning electron microscopy. The process was optimized by various processing parameters, such as the composition of the emulsion system and the speed and time of emulsification. The colloidosomes with the highest surface coverage were used to prepare the Janus nanoplatelets by decorating the exposed surfaces of the barium hexaferrite nanoplatelets with gold nanospheres using mercaptan chemistry. Transmission electron microscopy was used to inspect the barium-hexaferrite/gold Janus nanoplatelets that were prepared for the first time

Particle size effects on the structure and emission of Eu3+:LaPO4 and EuPO4 phosphors

The authors acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056). T.G acknowledges to the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001).This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100 nm), 4 × 20 nm nanorods and 5 nm spheres (depending on the annealing temperature), 2 × 15 nm nanorods, and ultra-small spheres (2 nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2 Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592 nm (5D0→7F1), at 612 nm (5D0→7F2), at 652 nm (5D0→7F3) and at 684 nm (5D0→7F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle's morphology.Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Structure and enhanced antimicrobial activity of mechanically activated nano TiO2

Titanium dioxide is a photocatalyst, known not only for its ability to oxidize organic contaminants, but also for its antimicrobial properties. In this article, significant enhancement of the antimicrobial activity of TiO2 (up to 32 times) was demonstrated after its activation by ball milling. The antimicrobial activity was analyzed for one fungal and 13 bacterial ATCC strains using the microdilution method and recording the minimum inhibitory concentration (MIC) values. In order to further investigate the correlation between the mechanical activation of TiO2 and its antimicrobial activity, the structure, morphology and phase composition of the material were studied by means of Electron Microscopy, X-ray diffraction and nitrogen adsorption-desorption measurements. UV-Vis diffuse reflectance spectra were recorded and the Kubelka-Munk function was applied to convert reflectance into the equivalent band gap energy (E-g) and, consequently, to investigate changes in the E-g value. X-ray photoelectron spectroscopy was used to analyze the influence of mechanical activation on the Ti 2p and O 1s spectra. The presented results are expected to enable the development of more sustainable and effective advanced TiO2-based materials with antimicrobial properties that could be used in numerous green technology applications

Luminescence of Cr3+ ions in ZnAl2O4 and MgAl2O4 spinels: correlation between experimental spectroscopic studies and crystal field calculations

Details of preparation, spectroscopic and structural studies along with crystal field calculations for two Cr3+ doped spinels MgAl2O4 and ZnAl2O4 are given in the present paper. Both compounds show efficient red emission at about 685 nm, which is due to the E-2(g) - GT (4)A(2g) spin-forbidden transition of Cr3+ ions located at the sites with D-3d local symmetry. Analysis of structure of the CrO6 clusters was performed; comparison of the crystal field effects in both compounds revealed that the low-symmetry splitting of the orbital triplet states is more pronounced in ZnAl2O4. Both compounds show potential for applications as red-emitting phosphors. (c) 2016 Elsevier B.V. All rights reserved

Structural and Luminescent Properties of Y 2

The red phosphor Y2Mo4O15:Eu3+ calcined at different temperatures is obtained by a solid-state method, and is investigated in this article. Usage of solid-state method with the combination of five different calcination temperatures (500, 550, 600, 650, and 700 °C) leads to the formation of pure monoclinic phase in all samples apart from the one calcined at the lowest temperature. Crystallite size obtained by Rietveld refinement is in the range of 38–55 nm. Scanning electron microscopy analysis confirms the presence of agglomerates. Luminescence emission spectra and emission decay curves are measured for all pure samples, and parameters derived from these measurements are used for Judd–Ofelt analysis. International commission on illumination (CIE) chromaticity diagram confirms the presence of pure red emission and high quantum efficiency. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Multicolor-tunable emissions of YOF: Ln 3+ /Yb 3+ (Ln 3+ = Ho 3+ , Er 3+ , Tm 3+ ) nanophosphors

Color tuning of down-shifting and up-conversion emissions of YOF:Ln(3+)/Yb3+ (Ln(3+) = Er3+, Tm3+) nanophosphors is demonstrated. Nanophosphors were prepared by the modified sol-gel Pechini method and characterized by the X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Samples consist of 20 nm particles crystallized in the rhombohedral crystal structure. Depending on the Ln(3+) / Yb3+ concentration ratio and the type of excitation (UV/VIS or NIR) color of the particles emission varied from the blue to red. Commission Internationale de L'Eclairage chromaticity coordinates of emission colors are given for the range of Ln(3+)/Yb3+ concentration ratios for both down-shifting and up-conversion luminescence. We showed that the emission color of these nanophosphors may be additional tuned by simultaneous excitation with UV-VIS and NIR radiation (in different proportion) which yields unique color labels for the anti-counterfeit and security applications

Photoluminescence properties and thermal stability of RE2-xEuxSn2O7 (RE = Y3+, Gd3+, Lu3+) red nanophosphors: An experimental and theoretical study

Defect-fluorite structured Eu 3+ -doped Y 2 Sn 2 O 7 nanoparticles (30–40 nm) were successfully prepared through a facile co-precipitation method without any organic additives or templates followed by calcination in air. Luminescent properties of the as-prepared Y 2-x Eu x Sn 2 O 7 (0.02 ≤ x ≤ 0.6) nanophosphors were fully characterized from an experimental and theoretical point of view (excitation, emission, lifetime, critical concentration, temperature-dependent luminescence and thermal stability, type of interactions and the Judd-Ofelt analysis). The nanophosphors showed relatively sharp excitation bands from 360 to 530 nm and exhibited characteristic emission bands with the most intensive emission centered at 612 nm. In addition, Gd 1.98 Eu 0.02 Sn 2 O 7 and Lu 1.98 Eu 0.02 Sn 2 O 7 samples were prepared in order to study how substitution of RE 3+ (Y 3+ with Gd 3+ and Lu 3+ ions) influences on luminescent properties of RE 1.98 Eu 0.02 Sn 2 O 7 and thermal stability of their luminescence. In order to understand better luminescent properties, the Judd–Ofelt analysis was applied to all the synthesized powders. The highest value of quantum efficiency, ~96%, was estimated for Lu 1.98 Eu 0.02 Sn 2 O 7 . To assess potential application in high-power LEDs, the temperature-dependent emission spectra of Y 1.98 Eu 0.02 Sn 2 O 7 , Gd 1.98 Eu 0.02 Sn 2 O 7 and Lu 1.98 Eu 0.02 Sn 2 O 7 nanophosphors were studied. © 2019 Elsevier B.V

Efficient photocatalytic hydrogen production over titanate/titania nanostructures modified with nickel

Nickel-modified titanate/TiO2 catalysts were prepared by deposition of nickel ions onto hydrothermally prepared titanate supports, followed by hydrogen temperature-programmed reduction. Two different nickel precursors (hydroxide and carbonate) were used to tune reducibility and to vary the crystal phase structure of the final catalysts. The precursor reducibility and functional properties of the final catalysts were investigated systematically using various characterisation techniques. The results revealed a more facile reduction of the hydroxide precursor compared to its carbonate counterpart. Moreover, it was found that the formation of the anatase phase was favoured by the use of the hydroxide precipitation agent. The photocatalytic activity towards hydrogen production of the prepared catalysts was evaluated in the presence of 2-propanol under simulated solar light irradiation. A thorough study of the photocatalytic performance of the synthesised catalysts was conducted as a function of the precipitation agent used and the reduction temperature applied. The catalyst with dominant anatase crystal phase displayed the highest photocatalytic activity with a maximum H-2 production rate of 1040 mu mol h(-1) g(-1), this being more than four times higher than that of its carbonate counterpart. The catalysts with titanate structure showed similar activity, independent of the precipitation method used. The nanotubular structure was found to be the dominant factor in the stability of photocatalysts under long-run working conditions

MgTiO 3 :Mn 4+ a multi-reading temperature nanoprobe

International audienceMgTiO3 nanoparticles doped with Mn4+, with homogeneous size ranging about 63.1 ± 9.8 nm, were synthesized by a molten salt assisted sol gel method. These nanoparticles have been investigated as optical thermal sensors. The luminescence of tetravalent manganese ion in octahedral environment within the perovskite host presents drastic variations with temperature. Three different thermometry approaches have been proposed and characterized. Two luminescence intensity ratios are studied. Firstly between the two R-lines of Mn4+ emission at low temperature (−250 °C and −90 °C) with a maximal sensitivity of 0.9% °C−1, but also secondly between 2E → 4A2 (R-line) and the 4T2 → 4A2 transitions. This allows studying the temperature variation within a larger temperature range (−200 °C to 50 °C) with a sensitivity between 0.6% °C−1 and 1.2% °C−1 over this range. The last proposed method is the study of the lifetime variation versus temperature. The effective lifetime value corresponds to a combination of transitions from two excited energy levels of the tetravalent manganese (2E and 4T2) in thermal equilibrium toward the fundamental 4A2 state. Since the more energetic transition (4T2 → 4A2) is spin-allowed, contrary to the 2E → 4A2 one, the lifetime drastically decreases with the increase in temperature leading to an impressive high sensitivity value of 4.1% °C−1 at 4 °C and an exceptional temperature resolution of 0.025 °C. According to their optical features, MgTiO3:Mn4+ nanoparticles are indeed suitable candidates for the luminescence temperature probes at the nanoscale over several temperature ranges

Detailed study of structural and luminescent properties of Y2-xEuxZr2O7 (0 LT = x LT = 1) nanophosphors

Nanocrystalline Y2-xEuxZr2O7 (0 LT = x LT = 1) phosphor particles were prepared by polymer facilitated combustion and subsequent calcination at 800 degrees C. The thorough study of Eu-concentration influence on particles structure, morphology and luminescence is presented. This type of synthesis provides particles of similar to 5 nm in diameter, which crystallize in a defect fluorite structure (space group Fm-3m), and where each particle consists of a single crystallite, as revealed by X-ray diffraction and high-resolution transmission electron microscopy. With the increase of Eu concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller Y3+, while the shape and size of particles remain the same. Analysis of emission intensity and decay dependence on Eu concentration showed that this host material could be heavily doped with Eu since concentration quenching of emission occurs at high Eu content of 25-30 at.% (with respect to Y ions). The critical distance for energy transfer between Eu ions is estimated to 10.28 A and dipole-quadrupole interaction is found as the dominant mechanism responsible for the concentration quenching of emission. Radiative and non-radiative transition rates, the quantum efficiency of emission, Omega-intensity parameters, and branching ratios of Eu3+ emission are calculated for nanocrystals of all doping concentrations. It is found that more to-the-point expression 86% of emission comes from D-5(0) - GT F-7(2) and D-5(0) - GT F-7(1) transitions. Therefore, this phosphor emits pure red light with (0.661, 0.338) CIE color coordinates. (C) 2017 Elsevier B.V. All rights reserved