Luminescence properties of zirconia nanocrystals prepared by solar physical vapor deposition

Zirconia nanocrystals have attracted considerable interest as biolabels, which can be used as probes for medical imaging and biosensor applications. However, zirconia particle agglomeration forms a major limitation to its use for biolabeling. In this backdrop, for the first time, well-separated zirconia nanocrystals were obtained in a Heliotron reactor (PROMES CNRS, France) via the solar physical vapor deposition (SPVD) method. As the raw material target for solar evaporation, zirconia nanopowders obtained via the sol–gel process were used. The luminescence and upconversion luminescence properties of the Sol Gel nanopowders were compared with those of the SPVD nanocrystals. Erbium was chosen as the luminescence center with ytterbium as the sensitizer, and along with these two dopants, niobium was also used. Niobium acts as a charge compensator to compensate for depletion in the charge due to the introduction of trivalent erbium and ytterbium at tetravalent zirconium sites. Consequently, the oxygen-vacancy concentration is reduced, and this results in a significant increase in the upconversion luminescence.The SPVD-prepared samples showed less agglomeration and a fine crystal structure as well as high luminescence, and thus, such samples can be of great interest for biolabeling applications.     

New laser materials for diode pumped solid state lasers

Ytterbium (Yb³⁺) doped solid state lasers (e.g. Yb:YAG), pumped with InGaAs laser diodes, have been intensively and successfully developed recently. A search is in progress for novel ytterbium doped crystals possessing properties superior to known Yb doped gain media, or with properties enabling of Yb lasers with new capabilities. Several such materials have been identified and characterized in the past year.     

Titania-coated glass microballoons and cenospheres for environmental applications

Functional titania coatings on glass microballoons (GMBs) and cenospheres have a broad range of potential environmental applications, primarily in purification of drinking water and treatment of industrial wastewater. The heterogeneous photocatalytic capabilities of titania films and particles have been extensively examined in the literature as effective alternatives to current technologies. Although the chemistry of titania films for photocatalysis has been studied, titania-coated GMBs have not yet been extensively considered and the materials science aspects of the titania-GMB and titania-cenosphere systems have not been addressed. We have examined the microstructure, morphology, and mechanical properties of titania coatings on both cenospheres and commercially produced GMBs. Scanning electron microscopy was used to examine coating coverage and defects. Energy dispersive X-ray spectroscopy and Raman spectroscopy were used for element and phase identification, respectively. Hardness and modulus measurements of the titania coatings and the GMB and cenosphere materials were done by nanoindentation. Additionally, the photocatalytic activity of the titania-coated GMB system was tested on Procion Red dye using two different types of mixing, a magnetic stirrer and an aeration bubbler apparatus. The titania coatings showed good coverage and retention except in the case of magnetic stirring, where significant coating loss was observed.     

Electrorheological fluids containing Ce-doped titania

A new type of water-free electrorheological (ER) material of anatase titania doped with Ce has been synthesized by a sol-gel technique. The thermal character and crystal structure of doped titania are characterized with FT-IR, DSC-TG and XRD. The ER behaviors of the suspension made of such particles dispersed in silicone oil at a volume fraction of 18% are investigated in a DC electric field. The results show that the doped titania ER suspension has a much increased shear stress compared with the pure titania one. The shear stresses of 1.7 kPa at 3 kV/mm and 2.6 kPa at 4 kV/mm can be induced in a 8.5 mol% cerium-doped titania ER suspension, which is 5~times higher than that of the pure titania one. Moreover, the induced shear stress has a significant dependence on the Ce/Ti molar ratio and the maximum shear stress can be obtained when Ce/Ti molar ratio is about 0.1. In addition, significant differences in the temperature dependence of shear stress between the pure and doped titania ER suspensions are found. The working temperature range is extended by Ce doping. The obvious improvement in the ER effect resulting from Ce doping can be explained in terms of the dielectric and conduction properties of the ER suspensions.     

Nanopowders of YAl3(BO3)4 doped by Nd, Yb and Cr obtained by sol-gel method: Synthesis, structure and luminescence properties

Structure, morphology and luminescence properties of nanocrystalline samples of YAl₃(BO₃)₄ (YAB) undoped and doped with neodymium, ytterbium and chromium obtained by the sol-gel method are presented. The best results of synthesis are obtained for mannitol as polymerizing agent. Single phase of nanopowder is obtained for pure YAB. Dopants destroy the compound structure; two other compounds, namely Al₁₈B₄O₃₃ and YBO₃, were revealed by X-ray investigation. Nanopowders show isometric and needles forms, the calculated size of crystallites is about 60 nm. Their optical properties are determined and results are compared to data obtained for single crystal counterparts. It is shown that the influence of rare earth ions incorporated into YBO₃ phase on luminescent spectra and excited state relaxation dynamics of the nanopowders is negligibly small when the YBO₃ content is of the order of several wt%. Residual impurity phases do not affect significantly spectroscopic properties of YAB nanopowders.     

Luminescent and structural properties of Yb-doped Al2O3 nanopowders

In this work, we discuss structural and luminescent properties of Al₂O₃ nanopowders doped with Yb³⁺ ions prepared by a novel method, in which organic compounds were used as a solvent and lanthanide organic derivatives, served as a rare-earth ion source. The set of samples differing in activator concentrations and particle sizes was carefully studied by means of structural and optical characterization methods. In particular, the high resolution electron and transmission microscopy has been deployed together with X-ray diffraction technique to determine fundamental structural properties of nanopowders. The optical characterization was focused mainly on basic excitation and emission features and their sensitiveness on dopant concentration and the average nanoparticle size.     

Synthesis and characterization of undoped and TM (Co,Mn) doped ZnO nanoparticles

Antibacterial activity of Transition metals (Mn, Co) doped ZnO nanopowders prepared by a DC thermal plasma method against Escherichia coli and Staphylococcus aureus are investigated. The phase and morphology studies have been carried out by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. All the samples of the present investigation are found to have hexagonal wurtzite structure and crystallite sizes are found to vary from 25 nm to 30 nm. Our bacteriological study showed the enhanced antibacterial activity of transition metals doped ZnO nanoparticles than undoped ZnO indicating the great potential of ZnO nanoparticles in relevant clinical and biomedical applications.     

稀土铈改性二氧化钛微粉的制备及其介电性质

用Sol-gel法制备了掺杂稀土元素铈的二氧化钛微粉,测试了它的介电常数和电导率,由该材料作分散相与甲基硅油配制了无水电流变液,对其电常数和电导率增加,材料的电流变性能也发生很大的改变,存在一个稀土含是珠最佳浓度范围,在此区域介电常数取得最大值,电流变液的剪切强度也取得极大值,比纯二氧化钛电流变液的流变性能提高5倍以上。     

Synthesis of new materials by laser pyrolysis: ZrO2, Y2O3:Ce and TiC(x)N(y) nanoparticles

New developments concerning the synthesis of oxide and non oxide nanoparticles by laser pyrolysis are reported here. In order to be able to study the relations between the host and the guest in doped nanostructured luminescent oxide matrix, tetragonal ZrO2 nanoparticles were synthesized with sizes as low as 3 nm in weighable amounts. Y2O3 nanoparticles doped with Ce were also prepared with grains in the 10-20 nm size range. Concerning the non-oxide materials, TiC, TiN, and TiC(x)N(y) nanopowders were obtained from simple annealing treatments performed on TiO2/C nanocomposites grown by laser pyrolysis. The final crystalline phase was controlled by the initial C content and the annealing atmosphere. Once sintered, these materials will allow the study of the mechanical properties of nanostructured carbonitride ceramics.     

Effect of Microstructure on Electrorheological Property for Pure TiO2 Particle Material

Pure titanium dioxide （TiO2） particle materials were prepared by hydrolyzing titanium tetrachloride （TiCl4）. The microstructures of these materials were determined by X-ray diffraction （XRD）, accelerated surface area and porosimetry apparatus （BET）, and transmission electron microscopy （TEM）. The TiO2 materials obtained by calcinations under different temperatures distinctly revealed different microstructures in crystal structure type, surface area, pore size, pore volume and grain size. The relationship between the microstructure of the TiO2 materials and their electrorheological （ER） activity was investigated. Anatase titania particles have better ER performance than rutile titania particles. Amorphous TiO2 materials display higher ER activity than the crystalline titania materials. A large pore volume can be more advantageous in improving the ER effect of a particle material.     

Effect of Microstructure on Electrorheological Property for Pure Particle Material

Pure titanium dioxide (TiO2) particle materials were prepared by hydrolyzing titanium tetrachloride (TiCl4). The microstructures of these materials were determined by X-ray diffraction (XRD), accelerated surface area and porosimetry apparatus (BET), and transmission electron microscopy (TEM). The TiO2 materials obtained by calcinations under different temperatures distinctly revealed different microstructures in crystal structure type, surface area, pore size, pore volume and grain size. The relationship between the microstructure of the TiO2 materials and their electrorheological (ER) activity was investigated. Anatase titania particles have better ER performance than rutile titania particles. Amorphous TiO2 materials display higher ER activity than the crystalline titania materials. A large pore volume can be more advantageous in improving the ER effect of a particle material.     

Laser-assisted production of spherical TiO2 nanoparticles in water

TiO(2) nanoparticles with controllable average diameter have been obtained by laser ablation in water. A monomode ytterbium doped fiber laser (YDFL) was used to ablate a metallic titanium target placed in deionized water. The resulting colloidal solutions were subjected to laser radiation to study the resizing effect. The crystalline phases, morphology and optical properties of the obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray energy dispersive spectroscopy (EDS) and UV-vis absorption spectroscopy. The colloidal suspensions produced consisting of titanium dioxide crystalline nanoparticles show almost perfect spherical shape with diameters ranging from 3 to 40 nm. The nanoparticles are polycrystalline and exhibit anatase as well as rutile phases.     

3D experimental quantification of fabric and fabric evolution of sheared granular materials using synchrotron micro-computed tomography

Many experimental studies have demonstrated that mechanical response of granular materials is highly influenced by micro-structural fabric and its evolution. In the current literature, quantification of fabric and its evolution has been developed based on micro-structural observations using Discrete Element Method or 2D experiments with simple particle shapes. The emergence of X-ray computed tomography technique has made quantification of such experimental micro-structural properties possible using 3D high-resolution images. In this paper, synchrotron micro-computed tomography was used to acquire 3D images during in-situ conventional triaxial compression experiments on granular materials with different morphologies. 3D images were processed to quantify fabric and its evolution based on experimental measurements of contact normal vectors between particles. Overall, the directional distribution of contact normals exhibited the highest degree of isotropy at initial state (i.e., zero global axial strain). As compression progressed, contact normals evolved in the direction of loading until reaching a constant fabric when experiments approached the critical state condition. Further assessment of the influence of confining pressure, initial density state, and particle-level morphology on fabric and its evolution was formed. Results show that initial density state and applied confining pressure significantly influence the fabric-induced internal anisotropy of tested specimens at initial states. Relatively, a higher applied confining pressure and a looser initial density state resulted in a higher degree of fabric-induced internal anisotropy. Influence of particle-level morphology was also found to be significant particularly on fabric evolution.     

Synthesis, characterization and photocatalytic activity of porous manganese oxide doped titania for toluene decomposition

The present study describes the photocatalytic degradation of toluene in gas phase on different porous manganese oxide doped titanium dioxide. As synthesized birnessite and cryptomelane type porous manganese oxide were doped with titania and tested for photocatalytic decomposition of toluene in gas phase. The effects of the inlet concentration of toluene, flow rate (retention time) were examined and the relative humidity was maintained constantly. Thermal and textural characterization of manganese oxide doped titania materials were characterized by X-ray diffraction (XRD), thermogravemetry (TG), BET and TEM-EDAX studies. The aim of the present study is to synthesize the porous manganese oxide doped titania and to study its photocatalytic activity for toluene degradation in gas phase. Cryptomelane doped titania catalyst prepared in water medium [K-OMS-2 (W)] is shown the good toluene degradation with lower catalysts loading compared to commercial bulk titania in annular type photo reactor. The higher photocatalytic activity due to various factors such as catalyst preparation method, experimental conditions, catalyst loading, surface area, etc. In the present study manganese oxide OMS doped titania materials prepared by both aqueous and non-aqueous medium, aqueous medium prepared catalyst shows the good efficiency due to the presence of OH bonded groups on the surface of catalyst. The linear forms of different kinetic equations were applied to the adsorption data and their goodness of fit was evaluated based on the R2 and standard error. The goodness to the linear fit was observed for Elovich model with high R2 (>or=0.9477) value.     

Synthesis of TiO2 nanoparticles through the Gel Combustion process

Nanosized titania particles have been synthesized through the Gel Combustion process. The synthesis was carried out by starting from a common and low-cost titanium precursor and hydrogen peroxide as combustible substance. The process led to a significant gas development and the as-synthesized nanoparticles showed a low degree of crystallinity and mean dimension of 20 nm. Different thermal treatments were performed so as to investigate their effect on the structural properties and on the particle size of the synthesized products. The optimal temperature was set at 300 °C, giving pure anatase TiO₂ nanopowders with a good level of crystallinity, an average particle size of 50 nm and a high value of specific surface area.     

Organic acid precursor synthesis and environmental photocatalysis applications of mesoporous anatase TiO2 doped with different transition metal ions

Mn²⁺ and Co²⁺ ions doped titania (TiO₂) nanopowders were synthesized using organic acid precursor route for the first time. The results revealed that TiO₂ with metal dopants were reduced grain size and increased the surface area of TiO₂. The band gap energy values of doped TiO₂ were higher than the pure TiO₂ and show a blue shift. The photocatalytic performance of TiO₂ in the degradation of the rhodamine B dye was tested. Moreover, the efficiency was enhanced by adding Mn and Co to TiO₂.     

Emission properties of polymer composites doped with Er3+:Y2O3 nanopowders

In this work we report the recent results of our investigation on visible emission properties of the PMMA-based polymer nanocomposites doped with Er³⁺:Y₂O₃ nanopowders. The set of active nanopowders, and polymer films, differing in active ions concentration, was characterized with respect of their luminescent properties in the green spectral range, available to a limited extent for semiconductor lasers. In particular – the concentration dependent emission spectra and fluorescence dynamics profiles were measured under direct (single photon) and up-converted excitation, enabling the comparison of luminescent properties of developed nanocomposite materials and original nanopowders, optimization of erbium dopant concentration as well as discussion of excitation mechanisms and analysis of the efficiency of depopulation processes.     

V掺杂TiO2纳米管阵列的制备及光催化研究

以钒钛合金为原料,应用阳极氧化法制备出高度致密、有序的V掺杂TiO2纳米管阵列。应用扫描电镜(SEM)和粉末X光衍射仪(XRD)表征分析纳米管阵列的形貌和结构,结果表明在浓度不同的HF电解液下制备出径向不同的纳米管阵列,电解液浓度(0.5%～1.5%(质量分数)),管径变化(39.7～72.7nm)。在室温、可见光照射条件下,以10mg/L的亚甲基蓝溶液为模拟污染物进行光催化降解试验,研究了其光催化性能。结果显示V掺杂TiO2纳米管阵列光催化性能优于纯TiO2纳米管,且在HF电解液浓度为1.0%(质量分数)时制备出来的TiO2纳米管光催化降解有机毒物性能最佳。     

Energy coupled to matter for magnetic alignment of rare earth–doped alumina

Energy coupled to matter (ECM) concepts such as magnetic field–assisted processing were used to align rare earth–doped alumina ceramics in the presence of applied fields. The addition of gadolinium and ytterbium dopants to alumina increased the magnetic susceptibility anisotropies, and induced magnetic torques that led to significant alignment of ceramic particles under the application of magnetic fields as low as 1.8?T. In comparison, undoped alumina materials showed minimal alignment under applied field strengths as high as 9?T. Density function theory modeling indicated that the specific dopant type dictated changes in the magnetic properties of different rare earth–doped alumina systems by directly affecting the magnetic moment localization and magnetocrystalline anisotropy.     

Influence of processing conditions on the luminescence of YVO4:Eu nanoparticles

Single-phase YVO₄:Eu³⁺ nanopowders were synthesized by sol–gel combustion method using citric acid as a chelating agent and reducer. The microstructures and photoluminescence (PL) properties of the as-prepared YVO₄:Eu³⁺ nanopowders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and PL spectroscopy. The luminescence intensities of the YVO₄ nanoparticles doped with 5 mol% Eu³⁺ ions strongly depended on the calcination temperature, the molar ratio of citric acid to nitrates and the amounts of the Li⁺ additive.