Dual-center co-doped and mixed ratiometric LuVO4:Nd3+/Yb3+nanothermometers.

During last decade luminescence thermometry has become a widely studied research field due to its potential applications for real time contactless temperature sensing where usual thermometers cannot be used. Special attention is paid to the development of accurate and reliable thermal sensors with simple reading. To address existing problems of ratiometric thermometers based on thermally-coupled levels, LuVO4:Nd3+/Yb3+thermal sensors were studied as a proof-of-concept of dual-center thermometer obtained by co-doping or mixture. Both approaches to create a dual-center sensor were compared in terms of energy transfer efficiency, relative sensitivity, and temperature resolution. Effect of excitation mechanism and Yb3+doping concentration on thermometric performances was also investigated. The best characteristics ofSr = 0.34% K-1@298 K and ΔT = 0.2 K were obtained for mixed phosphors upon host excitation.

Fragmented graphene synthesized on a dielectric substrate for THz applications.

Fragmented multi-layered graphene films were directly synthesized via chemical vapor deposition (CVD) on dielectric substrates with a pre-deposited copper catalyst. We demonstrate that the thickness of the sacrificial copper film, process temperature, and growth time essentially influence the integrity, quality, and disorder of the synthesized graphene. Atomic force microscopy and Kelvin probe force microscopy measurements revealed the presence of nano-agglomerates and charge puddles. The potential gradients measured over the sample surface confirmed that the deposited graphene film possessed a multilayered structure, which was modelled as an ensemble of randomly oriented conductive prolate ellipsoids. THz time domain spectroscopy measurements gave theacconductivity of the graphene flakes and homogenized graphitic films as being around 1200 S cm-1and 1000 S cm-1, respectively. Our approach offers a scalable fabrication of graphene structures composed of graphene flakes, which have effective conductivity sufficient for a wide variety of THz applications.

Mechanical relaxation of functionalized carbosilane dendrimer melts.

Functionalizing the internal structure of classical dendrimers is a new way of tailoring their properties. Using atomistic molecular dynamics simulations, we investigate the rheological behavior of functionalized dendrimer (FD) melts obtained by modifying the branching of carbosilane dendrimers (CSD). The time (relaxation modulus G(t)) and frequency (storage G' and loss G'' moduli) dependencies of the dynamic modulus are obtained. Fourth generation FD melts present a region where G' > G''. In contrast, their non-functionalized counterparts (i.e., classical dendrimers with regular branching) do not show such a region. The comparative analysis of FD and CSD suggests that the internal densification due to functionalization prevents the penetration of branches and causes FD to behave like colloidal particles in a crowded environment. Since CSD have no special interactions, we expect that this effect will be common for other dendrimer macromolecules.

Al3+ solvation in solutions of aluminum nitrate in a protic ionic liquid: Nuclear magnetic resonance verification of the solvation shell composition.

The closest environment of Al3+ cations was analyzed in detail in solutions of aluminum nitrate in the prototypical protic ionic liquid ethyl ammonium nitrate (EAN) using 1 H and 14 N nuclear magnetic resonance (NMR) spectra. For Al (NO3 )3 -EAN mixtures with different water content, a quantitative analysis of the integral intensities of the 1 H and 14 N signals was carried out and the composition of the first solvation shell of the aluminum cation was refined.

Effect of crystal structure on the Young's modulus of GaP nanowires.

Young's modulus of tapered mixed composition (zinc-blende with a high density of twins and wurtzite with a high density of stacking faults) gallium phosphide (GaP) nanowires (NWs) was investigated by atomic force microscopy. Experimental measurements were performed by obtaining bending profiles of as-grown inclined GaP NWs deformed by applying a constant force to a series of NW surface locations at various distances from the NW/substrate interface. Numerical modeling of experimental data on bending profiles was done by applying Euler-Bernoulli beam theory. Measurements of the nano-local stiffness at different distances from the NW/substrate interface revealed NWs with a non-ideal mechanical fixation at the NW/substrate interface. Analysis of the NWs with ideally fixed base resulted in experimentally measured Young's modulus of 155 ± 20 GPa for ZB NWs, and 157 ± 20 GPa for WZ NWs, respectively, which are in consistence with a theoretically predicted bulk value of 167 GPa. Thus, impacts of the crystal structure (WZ/ZB) and crystal defects on Young's modulus of GaP NWs were found to be negligible.

Local dynamics in LiCl-CsCl-D2O water-in-salt solutions according to NMR relaxation.

The main purpose of this study was to investigate the local structure and dynamics in 'water-in-salt' solutions, namely the ternary concentrated LiCl-CsCl-D2O electrolytes. Water based electrolyte solutions are components of natural waters, they are very widespread and possess many practical abilities. NMR was applied as the main technique to study the local structure of the solutions as well as ion and solvent dynamics. The characteristic reorientation times (τc) were calculated from spin-lattice relaxation times for 2H, 7Li, and 133Cs nuclei. The diffusion coefficients (D) for 1H, 7Li, and 133Cs nuclei were also obtained. We have confirmed that most of the molecules and ions are combined into dynamic clusters, 'cybotactic groups', with lifetimes long enough for them to diffuse as a whole unit. Thus, the results provide direct experimental confirmation of the existence of 'cybotactic groups' predicted earlier for concentrated electrolyte solutions. The precise self-diffusion coefficients show the state of ions in the system and can be used as a reference for modelling of such systems.

Stable Deuterium Labeling of Histidine-Rich Lysine-Based Dendrimers.

Peptide dendrimers, due to their biocompatibility and low toxicity, are highly promising candidates as nanocarriers for drugs and genes. The development of this kind of delivery system requires reliable monitoring of their metabolic and biological pathways. In this respect, hydrogen isotope labeling has tremendous importance, being a safe tool for detection of the labeled nanocarriers. In this work, we have synthesized new histidine-rich lysine-based dendrimers (Lys-2His dendrimer) with two linear histidine (His) residues in every inner segment. The presence of His residues has enabled us to perform controlled deuteration of Lys-2His dendrimers. The high deuteration degree (around 70%) does not practically change after redissolving the samples in H2O and heating them at 40 °C, which indicates the isotopic label stability.

Molecular mobility in several imidazolium-based ionic liquids according to data of 1 H and 13 C NMR relaxation.

Temperature dependences are compared for 1 H and 13 C NMR 1/T1 curves relaxation rates in three imidazolium-based ionic liquids (ILs), namely, in [bmim]PF6 , [bmim]BF4 , and [emim]CH3 COO. 13 C curves show alike behavior for all three ILs and follow a well-known Bloembergen-Pound-Purcell (BPP) equation. On the contrary, an essential part of 1 H curves differ strongly from corresponding 13 C ones and also have different shapes for different ILs. For the first time, we have detected the specific, two-maximum shape of 1 H relaxation curve for hydrogen atom of C(2)H group of the [emim]CH3 COO. Assuming that this maximum reflects the correlated rotation of several adjoining ion pairs, we have tried to destroy this rotation by addition of glycerol to the [emim]CH3 COO. The second, high-temperature maximum has disappeared in the [emim]CH3 COO-glycerol mixture, and this fact confirms our assumption. Copyright © 2017 John Wiley & Sons, Ltd.

Young's Modulus of Wurtzite and Zinc Blende InP Nanowires.

The Young's modulus of thin conical InP nanowires with either wurtzite or mixed "zinc blende/wurtzite" structures was measured. It has been shown that the value of Young's modulus obtained for wurtzite InP nanowires (E[0001] = 130 ± 30 GPa) was similar to the theoretically predicted value for the wurtzite InP material (E[0001] = 120 ± 10 GPa). The Young's modulus of mixed "zinc blende/wurtzite" InP nanowires (E[111] = 65 ± 10 GPa) appeared to be 40% less than the theoretically predicted value for the zinc blende InP material (E[111] = 110 GPa). An advanced method for measuring the Young's modulus of thin and flexible nanostructures is proposed. It consists of measuring the flexibility (the inverse of stiffness) profiles 1/k(x) by the scanning probe microscopy with precise control of loading force in nanonewton range followed by simulations.

Molecular dynamics simulation of spin-lattice NMR relaxation in poly-L-lysine dendrimers: manifestation of the semiflexibility effect.

NMR relaxation experiments are widely used to investigate the local orientation mobility in dendrimers. In particular, the NMR method allows one to measure the spin-lattice relaxation rate, 1/T1, which is connected with the orientational autocorrelation function (ACF) of NMR active groups. We calculate the temperature (Θ) and frequency (ω) dependences of the spin-lattice NMR relaxation rates for segments and NMR active CH2 groups in poly-L-lysine (PLL) dendrimers in water, on the basis of full-atomic molecular dynamics simulations. It is shown that the position of the maximum of 1/T1(ω) depends on the location of the segments inside the dendrimer. This dependence of the maximum is explained by the restricted flexibility of the dendrimer. Such behavior has been predicted recently by the analytical theory based on the semiflexible viscoelastic model. The simulated temperature dependences of 1/T1 for terminal and inner groups in PLL dendrimers of n = 2 and n = 4 generations dissolved in water are in good agreement with the NMR experimental data, which have been obtained for these systems previously by us. It is shown that in the case of PLL dendrimers, the traditional procedure of the interpretation of NMR experimental data - when smaller values of 1/T1 correspond to higher orientation mobility - is applicable to the whole accessible frequency interval only for the terminal groups. For the inner groups, this procedure is valid only at low frequencies.

13C NMR relaxation and reorientation dynamics in imidazolium-based ionic liquids: revising interpretation.

The temperature dependencies of (13)C NMR relaxation rates in [bmim]PF6 ionic liquid have been measured and the characteristic times (τc) for the cation reorientation have been recalculated. We found the origin of the incorrect τc temperature dependencies that were earlier reported for ring carbons in a number of imidazolium-based ILs. After a correction of the approach (13)C T1, the relaxation data allowed us to obtain the characteristic times for an orientation mobility of each carbon, and a complicated experiment, such as NOE, was not required. Thus the applicability of (13)C NMR relaxation rate measurements to the calculation of the characteristic times for reorientation of all the carbons of the [bmim](+) cation was confirmed and our findings have shown that a (13)C NMR relaxation technique allowed its application to ionic liquids to be equally successful as for other liquid systems.

Effect of Plasmonic Ag Nanoparticles on Emission Properties of Planar GaN Nanowires.

The combination of plasmonic nanoparticles and semiconductor substrates changes the properties of hybrid structures that can be used for various applications in optoelectronics, photonics, and sensing. Structures formed by colloidal Ag nanoparticles (NPs) with a size of 60 nm and planar GaN nanowires (NWs) have been studied by optical spectroscopy. GaN NWs have been grown using selective-area metalorganic vapor phase epitaxy. A modification of the emission spectra of hybrid structures has been observed. In the vicinity of the Ag NPs, a new emission line appears at 3.36 eV. To explain the experimental results, a model considering the Fröhlich resonance approximation is suggested. The effective medium approach is used to describe the enhancement of emission features near the GaN band gap.

Upconverting NIR-to-NIR LuVO4:Nd3+/Yb3+ Nanophosphors for High-Sensitivity Optical Thermometry.

Accurate contactless thermometry is required in many rapidly developing modern applications such as biomedicine, micro- and nanoelectronics, and integrated optics. Ratiometric luminescence thermal sensing attracts a lot of attention due to its robustness toward systematic errors. Herein, a phonon-assisted upconversion in LuVO4:Nd3+/Yb3+ nanophosphors was successfully applied for temperature measurements within the 323-873 K range via the luminescence intensity ratio technique. Dual-activating samples were obtained by codoping and mixing single-doped nanopowders. The effect of the type of dispersion system and the Yb3+ doping concentration was studied in terms of thermometric performances. The relative thermal sensitivity reached a value of 2.6% K-1, while the best temperature resolution was 0.2 K. The presented findings show the way to enhance the thermometric characteristics of contactless optical sensors.

Average relaxation time of internal spectrum for carbosilane dendrimers: nuclear magnetic resonance studies.

A new theoretical description of the interior mobility of carbosilane dendrimers has been tested. Experiments were conducted using measurements of the (1)H NMR spin-lattice relaxation time, T(1H), of two-, three- and four-generation carbosilane dendrimers with three different types of terminal groups in dilute chloroform solutions. Temperature dependences of the NMR relaxation rate, 1/T(1H), were obtained for the internal CH(2)-groups of the dendrimers in the range of 1/T(1H) maximum, allowing us to directly evaluate the average time of the internal spectrum for each dendrimer. It was found that the temperature of 1/T(1H) maximum is practically independent of the number of generations, G; therefore, the theoretical prediction was confirmed experimentally. In addition, the average time of the internal spectrum of carbosilane dendrimers was found to be near 0.2 ns at room temperature, and this value correlates well with the values previously obtained for other dendrimer structures using other experimental techniques.

Modification Approaches to Enhance Dehydration Properties of Sodium Alginate-Based Pervaporation Membranes.

Transport characteristics of sodium alginate (SA) membranes cross-linked with CaCl2 and modified with fullerenol and fullerene derivative with L-arginine for pervaporation dehydration were improved applying various approaches, including the selection of a porous substrate for the creation of a thin selective SA-based layer, and the deposition of nano-sized polyelectrolyte (PEL) layers through the use of a layer-by-layer (Lbl) method. The impacts of commercial porous substrates made of polyacrylonitrile (PAN), regenerated cellulose, and aromatic polysulfone amide were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), standard porosimetry method, and water filtration. The effects of PEL combinations (such as poly(sodium 4-styrene sulfonate) (PSS)/SA, PSS/chitosan, PSS/polyacrylic acid, PSS/poly(allylamine hydrochloride)) and the number of PEL bilayers deposited with the Lbl technique on the properties of the SA and SA/fullerene derivative membranes were studied by SEM, AFM, and contact angle measurements. The best characteristics were exhibited by a cross-linked PAN-supported SA/fullerenol (5%) membrane with five PSS/SA bilayers: permeation flux of 0.68-1.38 kg/(m2h), 0.18-1.55 kg/(m2h), and 0.50-1.15 kg/(m2h), and over 99.7, 99.0, and 89.0 wt.% water in the permeate for the pervaporation dehydration of isopropanol (12-70 wt.% water), ethanol (4-70 wt.% water), and tetrahydrofuran (5.7-70 wt.% water), respectively. It was demonstrated that the mutual application of bulk and surface modifications essentially improved the membrane's characteristics in pervaporation dehydration.

Novel Mixed Matrix Sodium Alginate-Fullerenol Membranes: Development, Characterization, and Study in Pervaporation Dehydration of Isopropanol.

Novel mixed matrix dense and supported membranes based on biopolymer sodium alginate (SA) modified by fullerenol were developed. Two kinds of SA-fullerenol membranes were investigated: untreated and cross-linked by immersing the dry membranes in 1.25 wt % calcium chloride (CaCl2) in water for 10 min. The structural and physicochemical characteristics features of the SA-fullerenol composite were investigated by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic methods, scanning electron (SEM) and atomic force (AFM) microscopies, thermogravimetric analysis (TGA), and swelling experiments. Transport properties were evaluated in pervaporation dehydration of isopropanol in a wide concentration range. It was found that the developed supported cross-linked SA-5/PANCaCl2 membrane (modified by 5 wt % fullerenol) possessed the best transport properties (the highest permeation fluxes 0.64-2.9 kg/(m2 h) and separation factors 26-73,326) for the pervaporation separation of the water-isopropanol mixture in the wide concentration range (12-90 wt % water) at 22 °C and is suitable for the promising application in industry.

Gd3+-Doping Effect on Upconversion Emission of NaYF4: Yb3+, Er3+/Tm3+ Microparticles.

ß-NaYF4 microcrystals co-doped with Yb3+, Er3+/Tm3+, and Gd3+ ions were synthesized via a hydrothermal method using rare-earth chlorides as the precursors. The SEM and XRD data show that the doped ß-NaYF4 form uniform hexagonal prisms with an approximate size of 600-800 nm. The partial substitution of Y by Gd results in size reduction of microcrystals. Upconversion luminescence spectra of microcrystals upon 980 nm excitation contain characteristic intra-configurational ff bands of Er3+/Tm3+ ions. An addition of Gd3+ ions leads to a significant enhancement of upconversion luminescence intensity with maxima at 5 mol % of dopant.

Construction of efficient dual activating ratiometric YVO4:Nd3+/Eu3+ nanothermometers using co-doped and mixed phosphors.

The development of new contactless thermal nanosensors based on a ratiometric approach is of significant interest. To overcome the intrinsic limitations of thermally coupled levels, a dual activation strategy was applied. Dual activation was performed using co-doped single nanoparticles and a binary mixture of single-doped nanoparticles. Co-doped and mixed YVO4:Nd3+/Eu3+ nanoparticles were successfully demonstrated as luminescent nanothermometers and their thermometric performance, in terms of thermal sensitivity, temperature resolution and repeatability, was studied and compared.

Orientational mobility and relaxation spectra of dendrimers: Theory and computer simulation.

The developed theory of the orientational mobility of individual segments of a perfectly branched dendrimer is used to calculate the relaxation spectrum of a dendrimer. Frequency dependences of NMR relaxation 1/T(1) and of the nuclear Overhauser effect have been theoretically calculated from the Brownian dynamics simulation data. The dendrimer segmental orientational mobility is governed by three main relaxation processes: (i) the rotation of the dendrimer as a whole, (ii) the rotation of the dendrimer's branch originated from a given segment, and (iii) the local reorientation of the segment. The internal orientational mobility of an individual dendrimer segment depends only on the topological distance between this segment and the terminal shell of the dendrimer. Characteristic relaxation times of all processes and their contributions to the segmental mobility have been calculated. The influence of the number of generations and the number of the generation shell on the relaxation times has been studied. The correlation between the characteristic times and the calculated relaxation spectrum of the dendrimer has been established.

Lysine-based dendrimer with double arginine residues.

Due to their well-defined structure, multivalency, biocompatibility, and low toxicity, lysine dendrimers can be used as safe and efficient nanocarriers for drug and gene delivery. One useful strategy for improving the gene delivery properties of dendrimers is modification with arginine amino acid (Arg) residues. Incorporation of Arg residues could be favorable for the enhancement in transfection efficiency of lysine based dendrimers. In this work, we have synthesized a new second-generation poly-l-lysine dendrimer with repeating units containing two linear Arg residues between neighboring lysine branching points (Lys-2Arg dendrimer) and studied its physicochemical properties. We confirmed the structure of Lys-2Arg dendrimer using various one- and two-dimensional 1H and 13C NMR spectroscopy methods. Comparison of T 1H relaxation data for Lys-2Arg and Lys-2Lys dendrimers showed that the replacement of double Lys residues with double Arg residues resulted in a sharp decrease in the mobility of methylene groups in side segments and in the main chain of ε-Lys inner segments. We suggest that this unexpected effect is caused by a guanidine-guanidine pairing effect in water, which leads to entanglements between dendrimer branches.