Fabrication of nanocomposite particles with superparamagnetic and luminescent functionalities

A new kind of superparamagnetic luminescent nanocomposite particles has been synthesized using a modified Stöber method combined with an electrostatic assembly process. Fe₃O₄ superparamagnetic nanoparticles were coated with uniform silica shell, and then 3-aminopropyltrimethoxysilane was used to terminate the silica surface with amino groups. Finally, negatively charged CdSe quantum dots (QDs) were assembled onto the surface of the amino-terminated SiO₂/Fe₃O₄ nanoparticles through electrostatic interactions. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV-vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. Dense CdSe QDs were immobilized on the silica surface. The thickness of silica shell was about 35 nm and the particle size of the final products was about 100 nm. The particles exhibited favorable superparamagnetic and photoluminescent properties.     

Rare earth doped LiYbF4 phosphors with controlled morphologies: Hydrothermal synthesis and luminescent properties

High quality monodisperse LiYbF₄ microparticles with shape of octahedron had been prepared via a facile hydrothermal route. The crystalline phase, size, morphology and luminescence properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectra and Commission Internationale de L’Eclairage (CIE 1931) chromaticity coordinates, respectively. The influences of reaction temperature, reaction time and the molar ratio of EDTA to Yb³⁺ on the crystal phases and shapes of as-prepared products had been investigated in detail. The upconversion (UC) luminescence properties of LiYb_1?xF₄:xEr³⁺ (x =0.1, 0.2, 0.5, 1, 2, 5 and 10 mol%) particles with octahedral microstructures were studied under 976 nm excitation. The results showed that the luminescence colors of the corresponding products could be tuned to bright green by changing the doping concentration of Er³⁺ ion. The luminescence mechanisms for the doped Er³⁺ ion were thoroughly analyzed, showing great potential in applications such as biolabels, displays and other optical technologies.     

Cs frequency synthesis: a new approach

The paper describes a new approach to synthesizing the Cs hyperfine frequency of 9.192 GHz that is designed to be sufficiently rugged for use in space, specifically for the Primary Atomic Reference Clock in Space (PARCS) planned for the International Space Station, as well as ground applications. This new approach requires no narrow band filters or frequency multiplication, and the primary source of cooling is conduction. Instead of frequency multiplication, it uses a custom regenerative divider stage followed by two commercial binary dividers and several mixing stages. A fractional frequency step of 2x10(-17) is achieved by mixing the output of a 48-bit numerically controlled oscillator with the microwave signal. Preliminary tests on the new synthesizer design indicate an internal fractional frequency stability of 1x10(-15) at 10 s and 1x10 (-18) at 1 d, dominated by the daily room temperature variations. The phase and amplitude noise are similar to our previous designs that used frequency multiplication and narrow band filters. The temperature coefficient is less than 0.2 ps/K.     

Synthesis and optical properties of luminescent core-shell structured silicate and phosphate nanoparticles

Monodisperse, luminescent core-shell structured inorganic nanoparticles were synthesized by sol-gel technology. They exhibit an amorphous SiO₂ core and a crystalline luminescent shell. Zn₂SiO₄:Mn²⁺ and Ca₁₀(PO₄)₆OH:Eu³⁺ shell materials are investigated. The influence of the doping concentration on optical and structural properties was studied. The resulting nanoparticles were characterized by X-ray diffraction analysis, transmission electron microscopy, inductively coupled plasma optical emission spectrometry, and photoluminescence spectroscopy.     

Shell Scaffolds: A new approach towards high strength bioceramic scaffolds for bone regeneration

A key issue for bone tissue engineering is the design of bioceramic scaffolds combining high porosity with adequate mechanical properties. Furthermore, a resistant surface is required in order to have manageable samples for both in vivo and in vitro applications. Here a new protocol that aims at giving an appropriate response to these issues is developed. The realized shell scaffolds, obtained by combining a modified replication technique with the usual polymer burning-out method, look rather promising mainly thanks to their manageability, porosity and permeability. In this preliminary work the developed technique is discussed, together with an overview on the structure of the realized samples.     

Effects of initial precursor and microwave irradiation on step-by-step synthesis of zinc oxide nano-architectures

ZnO nano-architectures were produced with the aid of a fast, simple and low cost microwave-assisted synthesis method. Solid semispherical ZnO nanoparticles on the order of 600 nm in diameter along with rice-like ZnO nanorods 95 nm thick were produced from butanol, triethanolamine (TEA), and zinc acetate dihydrate. Solid spherical ZnO nano-architectures with an average diameter of 250 nm were produced from the same starting materials in addition to NaOH. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to characterize the ZnO nano-architectures as well as the precursor. This method is cheap, fast and simple; capable of producing large quantities of each ZnO nanostructure. Investigation of the step-by-step formation mechanism for each ZnO nanostructure was conducted.     

Novel approach to the synthesis of core-shell particles by sacrificial polymer shell method

In this work a new approach has been developed for the synthesis of SiO₂@Y₂O₃ particles with core-shell structure. The method is based on the synthesis of a covalently bonded sacrificial polymer shell grown onto silica particles. It is suitable to promote and stabilize the adsorption of different ions, namely Yttrium from its nitrate solution. After calcination and consequent elimination of the sacrificial polymer shell, the SiO₂@Y₂O₃ core-shell particles are obtained. Results reveal that the shell thickness of these core-shell particles is higher and more uniform than that of particles prepared without sacrificial polymer shell.     

A new precursor to electroconducting conjugated polymers: synthesis and opto-electrical properties of luminescent devices based on these PPV derivatives

A variety of novel conjugated PPV-related polymers have been synthesised using a synthetic approach that allows the tailoring of the chemical structure of the polymer backbone. In this way we have been able to prepare not only poly(p-phenylene vinylene) (PPV) (1), but also some electron-rich PPV derivatives such as poly(2,5-dimethyl-1,4-phenylene vinylene) (PDMetPV) (2) and poly(2,5-dimethoxy-1,4-phenylene vinylene) (PDMeoPV) (3) and PPV derivatives with an enlarged aromatic system, poly(4,4′-bisphenylene vinylene) (PBPV) (4) and poly(2,6-naphtaln vinylene) (PNV) (5). These materials were characterised in terms of molecular weight (GPC), elimination temperature (TGA, FT-IR), optical properties (UV-VIS), photoluminescence (PL) and device characteristics of the LEDs.     

Sol-gel synthesis and luminescent properties of nanocrystalline YAP:Mn

The work describes results of synthesis of Mn-doped YAP nanocrystalline samples by the sol-gel method and characterization of the material by X-ray powder diffraction, scanning electron microscopy and luminescence techniques. It was revealed that obtained in such a way YAP samples posses rather poor radiation storage properties that is interpreted by the uniform near-equilibrium synthesis conditions that does not allow formation of Y_Al antisite ions required for electrons trapping. On the other hand, the sol-gel method can be suggested as a suitable technique for obtaining of highly stoichiometric and not defected structure material without parasitic charge capturing and recombination processes that is very essential e.g. for scintillator materials.     

Metrology-cybernetics-control: A new approach

As a science and as a special activity concerned with measurements, the science of metrology pursues a classical, orthodox purpose, mainly involving the measurement of physical quantities. The term “measurement” is now applied also to social, economic, medical, and other disciplines, including cybernetics and problems of management and control. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 17–20, July, 1996.     

A simple synthesis of amine-derivatised superparamagnetic iron oxide nanoparticles for bioapplications

Adsorption of 3-aminopropyltriethoxysilane (APTS) on magnetite nanoparticles during its formation has been investigated to optimise the preparation of stable aqueous dispersion of amine derivatised magnetite nanoparticles. APTS adsorbs chemically on the surface of magnetite particle modifying its surface which is evident from thermal and C, H, N analysis. The variation of particle size has been observed with change of APTS concentration. X-ray diffractogram shows the formation of pure inverse spinel phase magnetite with average crystallite size 7 nm when equimolar (Fe₃O₄: APTS = 1:1) quantity of APTS was used during its synthesis. The presence of free surface –NH₂ groups and Fe–O–Si bonds was observed by FTIR. Raman spectrum further confirms the presence of surface –NH₂ groups. Transmission electron microscopy shows formation of particles of average size between 7 nm and 12 nm. The effective hydrodynamic diameter of the APTS coated particle agglomerates is 45.8 nm in stable aqueous colloidal dispersion, which is evident from photon correlation spectroscopy. VSM measurements at room temperature of both silanised and unsilanised magnetite shows their superparamagnetic nature with saturation magnetisation 41 e.m.u/g and 56 e.m.u/g, respectively. Avidin has been immobilised on the surface through glutaraldehyde, which demonstrates the possibility of the synthesised material to be used in protein immobilisation to form bioactive magnetic particles.     

A facile solution-phase approach to the synthesis of luminescent europium methacrylate nanowires and their thermal conversion into europium oxide nanotubes

Novel one-dimensional (1D) nanostructures of rare earth complexes (europium methacrylate (Eu(MA)(3))) have been prepared from the precursor of irregularly shaped Eu(MA)(3) powder in ethanol solvent without the assistance of an added surfactant, catalyst, or template. These hexagonal-shaped complex nanowires have diameters of about 100-300?nm and lengths ranging from tens to hundreds of micrometers. Nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) studies and thermogravimetric analysis (TGA) show that the precursor powder and the resulting nanowires have identical compositions. Under UV light excitation, strong red fluorescence can be clearly seen throughout the whole wires. This good luminescence characteristic of the complex nanowires is further confirmed by the fluorescence spectrum where strong and narrow emission can be seen. These rare earth complex nanowires provide a useful source for 1D rare earth oxide materials, as the europium ions are distributed uniformly in the Eu(MA)(3) nanowires. Through calcination, the Eu(MA)(3) nanowires are successfully converted into Eu(2)O(3) nanotubes. X-ray investigation confirms that the Eu(2)O(3) nanotubes have a cubic body-centered structure. FTIR measurements and TGA analysis are used to follow the calcination process. A plausible mechanism responsible for the formation of Eu(2)O(3) nanotubes is presented.     

Controlled synthesis and multifunctional properties of FePt-Au heterostructures

In this work, FePt-Au heterostructured nanocrystals (HNCs) such as tadpole-, dumbbell-, bead-, and necklace-like nanostructures were synthesized by a facile heteroepitaxial growth of Au NCs onto FePt nanorods (NRs). A study of the growth mechanism revealed that the morphology control of the final products can be correlated with the adsorption sites of hydrogen onto the FePt NRs, which can be manipulated by the amount of the forming gas (Ar/7% H₂) added. Not only the optical characteristic and magnetic properties of the intrinsic materials were retained in the products, but also the FePt-Au HNCs showed the tunable multifunctional properties resulted from the interactions between Au and FePt. Moreover, for methanol oxidation, the FePt-Au HNCs exhibited enhanced catalytic activity and CO tolerance on the catalyst surface compared to commercial Pt catalysts. It is worth noting that as multifunctional units, the FePt-Au HNCs also possess a heterogeneous surface, which could potentially enable their site-specific functionalization for targeting or imaging purposes in biomedical applications. More interestingly, the catalytic properties of the FePt-Au HNCs also endow this material with application potentials in nanocatalysis.      

New synthesis approach for low temperature bimetallic nanoparticles: size and composition controlled Sn-Cu nanoparticles

A various size of Sn-Cu nanoparticles were synthesized by using a modified polyol process for low temperature electronic devices. Monodispersive Sn-Cu nanoparticles with diameters of 21 nm, 18 nm and 14 nm were synthesized. In addition, the eutectic composition shift was also observed in nano-sized particles as compared with bulk alloys. By controlling the size and eutectic composition, a significant melting temperature depression of 30.3 degrees C was achieved. These melting temperature depression approaches will reduce adverse thermal effects in electronic devices and provide the synthesis guidelines for bimetallic nanoparticles with a low melting temperature.     

核-壳含氟硅织物整理剂的可控制备及其表征

采用电子转移活化再生催化剂原子转移自由基聚合(ARGET ATRP)引发含氟丙烯酸酯单体在纳米SiO2表面上的聚合反应,合成核-壳型含氟硅聚合物乳液,并用于棉织物的拒水拒油整理。聚合反应动力学表明酯单体在SiO2表面的聚合是一个活性可控的过程,所得聚合物分子量大小可控、分子量分布较窄。利用FT-IR、1 H NMR、19F NMR、XPS以及TEM等对聚合物乳液的结构和形态进行表征分析,证明其核-壳结构及氟的存在。所合成的纳米级聚合物乳液通过与织物表面形成微纳二元阶层结构,提高其拒水拒油性。     

水热法制备GdVO_4∶Tm蓝色纳米荧光粉体

采用水热法以十二烷基苯磺酸钠为活性剂合成了蓝色纳米荧光GdVO4:Tm粉体。用X射线衍射、扫描电镜、荧光光谱(PL)研究不同反应时间、反应物浓度和Tm3+掺杂量等条件下所得产物的结构和发光性能。结果说明,所得的产物为单一的四方锆型GdVO4:Tm晶体,颗粒大小约为20～50nm;GdVO4:Tm能够被200～320nm的紫外光激发,在278nm波长紫外光激发下发出波长为476nm的明亮蓝光,发光强度分别在反应物浓度为0.205mol/L时、反应时间为3d和Tm3+掺杂量为2%时最高。     

Co-precipitation synthesis and luminescent properties of indium-substituted YAG: Ce3+

Cerium-doped yttrium aluminum indium garnet (YAG: Ce³⁺) yellow phosphor was prepared by using the co-precipitation method. The impacts of In³⁺ concentration onto the properties were investigated and analyzed by X-ray diffraction, infrared spectra, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results indicated that the co-precipitation method adopted favored the ultrafine powders and achieved In³⁺ substitution for part of Al³⁺, leading to the large crystal plane spacing, and a blue shift occurred in the indium-substituted YAG: Ce³⁺ emission.     

Beta-MnO2/SiO2 core-shell nanorods: synthesis and dielectric properties

Large-scale beta-MnO2/SiO2 core-shell nanorods were synthesized by hydrolysis process. The product was characterized by XRD, EDS, SEM and TEM. The thickness of the SiO2 shell layer is about 3 nm approximately 5 nm, which can be tuned by changing the amount of tetraethyl orthosilicate (TEOS) and the reaction time. The dielectric properties of the synthesized core-shell nanorods at the temperature range from 373 K to 773 K in X-band were investigated in detail and the mechanism of the dielectric response was discussed. The dielectric loss of the SiO2-coated MnO2 nanorods at 773 K was about twice than that at 373 K. The high dielectric loss is mainly attributed to the interfacial polarization and the electromagnetic impedance match between the SiO2 shell layer and MnO2 core layer. The quantitative formula between the permittivity of beta-MnO2/SiO2 core-shell nanorods and the thickness of the SiO2 shell is established, which can be used to tune the dielectric properties of the core-shell nanorods through controlling the thickness of the SiO2 shell layer.     

A new yellowish green luminescent material SrMoO4:Tb

A novel yellowish green phosphor tervalent terbium (Tb³⁺) doped strontium molybdate (SrMoO₄) was synthesized by conventional solid-state reaction method and its crystal structure and luminescent properties are investigated in this paper. The X-ray diffraction patterns (XRD) showed that the phosphor sintered at 750 °C for 3 h was a pure SrMoO₄ phase. The excitation spectrum consisted of two bands and the two excitation peaks located at 375 nm and 488 nm respectively. The emission spectrum was composed of four narrow bands, in which the strongest emission was located at 548 nm. The particle size analysis indicated that the median particle size D₅₀ = 2.89 μm and range of particle size distribution was narrow. These results showed that the SrMoO₄:Tb³⁺ phosphor was a promising yellowish green phosphor for ultraviolet light emitting diode (UVLED) and blue LED based white LED. The appropriate concentration of Tb³⁺ was 5 mol% for the highest emission intensity at 548 nm. Natrium ion (Na⁺) was found to be a promising charge compensator for SrMoO₄:Tb³⁺ phosphor.     

Fabrication and luminescent enhancement of Eu3+-doped Y2O3@YOF core-shell nanocrystals

In this paper, a two-step synthesis method for preparing Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals is introduced. Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals were prepared by combining an autocombustion process with a low temperature solid state reaction. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), photoluminescence (PL) and fluorescence decay were employed to characterize the prepared samples. The results of XRD, TEM and EDS indicated that the products prepared by this method were not a mixture of Y2O3:Eu3+ and YOF:Eu3+ nanocrystals, but Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals. Compared with Y2O3:Eu3+ nanocrystals, a 20% increment in luminescence intensity was observed in the Eu3+ ion-doped Y2O3@YOF core-shell nanocrystals, thus suggesting that coating with a YOF:Eu3+-shell can efficiently block the nonradiative relaxation channels that are induced by surface defect states.