One-pot facile synthesis and optical properties of porous La2O2CO3 hollow microspheres

Lanthanum oxycarbonate (La₂O₂CO₃) hollow microspheres with novel porous architectures were successfully fabricated by a simple one-pot hydrothermal treatment of an aqueous solution containing glucose, La(NO₃)₃·6H₂O, and subsequent calcination. The as-prepared La₂O₂CO₃ porous hollow spheres are composed of nanoparticles with a mean particle size of 15 nm. Carbon microspheres act as not only templates but also carbon sources for the formation of La₂O₂CO₃ hollow spheres. Interestingly, the as-prepared La₂O₂CO₃ hollow spheres show a green emission band under UV excitation, which may be used as fluorescent biological labels.     

Hydrothermal synthesis and photoluminescence of Ce and Tb doped La2Sn2O7 nanocrystals

Phase-pure Ce-/Tb-doped and co-doped lanthanum stannates (La₂Sn₂O₇) nanocrystals were synthesized by a co-precipitation process combined with hydrothermal techniques without any further heat treatment. The crystal structure, particle size, morphologies, and photoluminescence properties of the as-synthesized products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The as-prepared samples were single-phase cubic pyrochlore-type nanocrystals with a typical size of 10-20 nm. PL spectra showed a dominating green-emitting line around 544 nm attributing to ⁵D₄-⁷F₅ magnetic dipole transition for Tb³⁺ doped and Ce³⁺/Tb³⁺ co-doped La₂Sn₂O₇ nanocrystals. Meanwhile, the concentration quenching phenomenon was observed in both La_2−xTb_xSn₂O₇ and La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals. Furthermore, an interesting enhancement of the energy transfer induced green emission was observed in the as-synthesized La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals.     

Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors

Spherical and rod like nanocrystalline Nd₂O₃ phosphors have been prepared by solution combustion and hydrothermal methods respectively. The Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd₂O₃ has been obtained with calcination at 900 °C for 3 h and the lattice parameters have been evaluated by Rietveld refinement. Surface morphology of Nd₂O₃ phosphors show the formation of nanorods in hydrothermal synthesis whereas spherical particles in combustion method. TEM results also confirm the same. Raman studies show major peaks, which are assigned, to F_g and combination of A_g + E_g modes. The PL spectrum shows a series of emission bands at ∼326-373 nm (UV), 421-485 nm (blue), 529-542 nm (green) and 622 nm (red). The UV, blue, green and red emission in the PL spectrum indicates that Nd₂O₃ nanocrystals are promising for high performance materials and white light emitting diodes (LEDs).     

Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO₂ and Fe₂O₃ (up to 10 mol%) have been prepared by mechanochemical milling of TiO₂ and yellow Fe₂O₃/red Fe₂O₃/precipitated Fe (OH)₃ using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO₂/Fe₂O₃) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO₂ having 5 mol% of Fe₂O₃ (YFT1) is 3-5 times higher photoactive than that of P25 TiO₂. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe₂O₃/TiO₂ attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe₂O₃/TiO₂ particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. EPR and magnetic susceptibility show that Fe³⁺ is in low spin state corresponding to μ_B = 1.8 BM. The temperature variation of μ_B shows that Fe³⁺ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe³⁺ in TiO₂/Fe₂O₃ alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.     

Microstructure and characterization of La2O3 and CeO2 doped diamond-like carbon nanofilms

Seven kinds of hydrogen-free La₂O₃ and CeO₂ doped DLC films with thickness of 220-280 nm were deposited on Si (100) substrates by unbalanced magnetron sputtering. Nanoparticles with diameter of 20-30 nm are formed on the surface of films. The surface roughness Ra of films is in the range of 1.5-2.0 nm. C, La, Ce and O elements distribute uniformly along the depth direction, and C, La, and Ce elements diffuse into the Si substrate at the interface. X-ray photoelectron spectroscopy confirms that the La₂O₃ and CeO₂ form within the DLC amorphous films, and Raman spectra indicate the obvious amorphous characteristics of DLC films. High-resolution transmission electron microscopy shows the nanocrystallines structure with diameter of 2-3 nm of 16% La₂O₃ and 10% CeO₂ doped DLC films, and Fourier transformation spectroscopy also exhibits the obvious crystalline characteristics. In this work, the microstructure of two kinds of rare earth oxides doped DLC composite films is measured and analyzed.     

Hydrothermal synthesis of MnCO3 nanorods and their thermal transformation into Mn2O3 and Mn3O4 nanorods with single crystalline structure

MnCO₃ nanorods with diameters of 50-150 nm and lengths of about 1-2 μm have been prepared for the first time by a facile hydrothermal method. Mn₂O₃ and Mn₃O₄ nanorods were obtained via the heat-treatment of the MnCO₃ nanorods in air and nitrogen atmosphere, respectively. The morphology and structure of the as-synthesized MnCO₃, Mn₂O₃ and Mn₃O₄ nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. It was found that the MnCO₃ nanorods are single-crystalline, and their morphology and single-crystalline characteristic can be sustained after thermal transformation into Mn₂O₃ and Mn₃O₄. The corresponding growth directions for MnCO₃, Mn₂O₃ and Mn₃O₄ nanorods were [2 1 4], [1 0 0] and [1 1 2], respectively. When applied as anode materials for lithium ion batteries, the Mn₂O₃ and Mn₃O₄ nanorods exhibited a reversible lithium storage capacity of 998 and 1050 mAh/g, respectively, in the first cycles.     

One-pot synthesis of polyaniline/Fe3O4 nanocomposites with magnetic and conductive behaviour. Catalytic effect of Fe3O4 nanoparticles

Polyaniline/Fe₃O₄ nanocomposites were prepared by a one-pot synthesis using N-(4-aminophenyl)aniline as the reagent, molecular oxygen or hydrogen peroxide as the oxidizing agents in the presence of Fe₃O₄ nanoparticles (NPs) in powder and ferrofluid form. Both magnetic NPs in powder and ferrofluid form showed similar catalytic behaviour. The catalytic effect is particularly evident when molecular oxygen was used as the oxidizing agent. However, concerning the morphological aspects, only the composites prepared in the presence of ferrofluid-type Fe₃O₄ NPs showed a preferential morphology of nanorods (between 30 and 110 nm in diameter). All the composites are superparamagnetic at room temperature but at low temperature they are in a blocked state. Inter-particle interactions significantly affect the magnetic properties of the composites. The electrical conductivity of the composites is about 10⁻² S cm⁻¹, in agreement with the values obtained for polyaniline prepared by chemical route. A mechanism of the nanorods formation is proposed.     

Preparation and properties of sintered molybdenum doped with La2O3/MoSi2

Sintered Mo with the addition of La₂O₃/MoSi₂ was prepared via the process of solid–solid doping + powder metallurgy. X-ray diffraction experiment, hardness test, three-point bending test and high-temperature tensile test were carried out to characterize the samples. The XRD pattern of a typical sample shows that the sintered Mo was mainly composed of Mo, La₂O₃ and Mo₅Si₃. Mo₅Si₃ was probably formed through the reaction between MoSi₂ and the Mo matrix. Densities and fracture toughnesses of both doped Mo and pure Mo were measured and contrasted. Sintered Mo with the addition of 0.2 wt% La₂O₃/MoSi₂ has the highest toughness, while more addition of La₂O₃/MoSi₂ has smaller effect on improving toughness or even embrittles Mo. The results of three-point bending test and high-temperature tensile test show that the bending strength and high-temperature tensile strength of doped Mo are both higher than those of pure Mo. The formation of Mo₅Si₃ improves the high-temperature strength. The La₂O₃/Mo₅Si₃ dispersed in the Mo matrix refined the grains, and thus strengthened the Mo matrix by dispersion strengthening and grain refinement.     

Effect of La2O3 on corrosion resistance of laser clad ferrite-based alloy coatings

The ferrite-based alloy powders with different contents of La₂O₃ were laser clad on a steel substrate. The microstructural features and phase structure of these coatings were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results showed that the microstructure of the coatings with La₂O₃ was refined and purified. The main phase of the coatings was γ (Fe, Ni). Moreover, the electrochemical properties of the coatings were investigated by anodic polarization curves and electrochemical impedance spectroscopy (EIS). Anodic polarization results indicated that both polarizing voltage and polarization current density were reduced with the addition of La₂O₃. EIS results showed that, with the increment of La₂O₃, the inductive arcs shrunk and capacitive arcs expanded. The inductive arc at low frequency was disappeared and changed to capacitive arc thoroughly when the content of La₂O₃ reached 1.2 wt.%. The corrosion weight loss experiment results showed that the corrosion rate was lower and the corrosion attack was lighter in the coatings with La₂O₃ than that without La₂O₃, resulting in a substantial improvement of the corrosion resistance.     

The Mn-doping effect on the charge ordering state of La1/3Sr2/3FeO3

The longitudinal ultrasonic velocity (V_l), as well as resistivity has been measured in single-phase polycrystalline La_1/3Sr_2/3Fe_1−xMn_xO₃ (x = 0, 0.025, 0.05) at a frequency of 10 MHz, from 20 K to 300 K. It is found that with increasing Mn-doping level, the resistivity increases and the charge ordering transition temperature T_CO shifts to lower temperature. For all samples, upon cooling down from 300 K, a substantial softening in V_l above T_CO and dramatic stiffening below T_CO are observed. This abnormal elastic softening above T_CO can be described well by the mean-field theory, which indicates that this feature is due to the electron-phonon coupling via the Jahn-Teller effect and this coupling is enhanced with the Mn doping. Below T_CO, another softening in V_l is observed for x = 0, and weakens with the increasing of Mn content. This character is attributed to the breathing-type distortion of Fe-O octahedron and suggests that the charge disproportionation (CD) transition is suppressed by the Mn substitution.     

Electronic structures and Eu photoluminescence behaviors in Y2Si2O7 and La2Si2O7

The electronic structures and linear optical properties of Y₂Si₂O₇ (YSO) and La₂Si₂O₇ (LSO) are calculated by LDA method based on the theory of DFT. Both YSO and LSO are direct-gap materials with the direct band gap of 5.89 and 6.06 eV, respectively. The calculated total and partial density of states indicate that in both YSO and LSO the valence band (VB) is mainly constructed from O 2p and the conduction band (CB) is mostly formed from Y 4d or La 5d. Both the calculated VB and CB of YSO exhibit relatively wider dispersion than that of LSO. In addition, the CB of YSO presents more electronic states. Meanwhile, the VB of LSO shows narrower energy distribution with higher electronic states density. The theoretical absorption of YSO shows larger bandwidth and higher intensity than that of LSO. The results are compared with the experimental host excitations and impurity photoluminescence in Eu³⁺-doped YSO and LSO.     

Preparation and structural properties of Lu2O3:Eu submicrometer spherical phosphors

Monodisperse non-agglomerated Lu₂O₃:Eu³⁺ submicrometer spheres were obtained by the homogeneous precipitation technique with subsequent annealing for spheres crystallization. The morphological and structural parameters of the Lu₂O₃:Eu³⁺ crystalline spheres prepared were investigated by the electron microscopy methods, thermal analysis (TG-DTA), X-ray diffractometry (XRD), X-ray photoelectron (XPS) and FT-IR spectroscopy. The influence of the annealing temperature on the morphology and sphericity was shown. Eu³⁺-doped lutetium oxide spheres were characterized by effective luminescence under X-ray excitation in the λ = 575-725 nm range corresponding to ⁵D₀ → ⁷F_J transitions (J = 0-4) of Eu³⁺ ions. It was shown that the X-ray luminescence efficiency of the Lu₂O₃:Eu³⁺ spherical phosphors prepared strongly depend on annealing temperature and dopant concentration.     

Charge compensation, electrical and dielectric behavior of lanthanum doped CaCu3Ti4O12

Mechanism of charge compensation on lanthanum, (La³⁺) substitution on Ca site in calcium copper titanate (CaCu₃Ti₄O₁₂), and its effect on resulting electrical and dielectric properties has been studied in the present investigation. For this purpose samples were prepared according to two stoichiometries viz. La_xCa_(1−3x/2)Cu₃Ti₄O₁₂ (x ≤ 0.09) and La_xCa_(1−x)Cu₃Ti₄O₁₂ (x = 0.03) by solid state ceramic route. The former represents ionic compensation while the later is in accordance with electronic compensation. Nature of charge carriers is identified by measuring Seebeck coefficient which is found to be negative in the entire range of measurement. In order to understand the mechanism of conduction, ac conductivity is measured as a function of temperature and frequency. Space charge polarization is the dominant polarization mechanism phenomenon at low frequency and high temperature while orientation polarization dominates at low temperature and high frequency. Impedance analysis confirms the formation of internal barrier layers which is responsible for high dielectric constant in these samples.     

Upconversion luminescence in Er/Yb codoped Y2CaGe4O12

Calcium yttrium tetrametagermanates Y₂CaGe₄O₁₂ doped with Er³⁺ and Er³⁺/Yb³⁺ reveal upconversion emission in visible spectral range under near-infrared excitation, λ_ex = 980 nm. For the solid solution Er_xY_2−xCaGe₄O₁₂ concentration dependencies for the green and red lines of the visible emission around 526 nm (²H_11/2 → ⁴I_15/2), 545 nm (⁴S_3/2 → ⁴I_15/2) and 670 nm (⁴F_9/2 → ⁴I_15/2) show the optimal value for the sample x = 0.2. The power dependence of the visible luminescence measured at room temperature in the low-power limit indicates two-photon upconversion process. Direct intensification of the upconversion emission signals has been achieved by ytterbium sensitizing. The other upconversion excitation mechanism in Y₂CaGe₄O₁₂:Er³⁺ is discussed for an 808 nm incident laser irradiation. A scheme of excitation and emission routes involving ground/excited state absorption, energy transfer upconversion, nonradiative multiphonon relaxation processes in trivalent lanthanide ions in Y₂CaGe₄O₁₂:Er³⁺ and Y₂CaGe₄O₁₂:Er³⁺, Yb³⁺ has been proposed. Conditions for visible emission occurrence under quasi-resonance λ_ex = 1064 nm excitation depending on pump power values are considered. In the low-power regime only near-infrared emission caused by the transition ⁴I_13/2 → ⁴I_15/2 in erbium ions has been detected.     

Sample thickness dependence of giant magnetoimpedance under low fields for La0.67Sr0.33Mn0.98Co0.02O3 manganites

The La_0.67Sr_0.33Mn_0.98Co_0.02O₃ plate sintered at 1250 °C shows a low field magnetoresistance (LFMR) effect under fields H < 4.6 kOe. However, the DC magnetoresistance ΔR/R₀ is very small, only −1.84% under H = 4.6 kOe. The character of helical growth was observed on grain surface of La_0.67Sr_0.33Mn_0.98Co_0.02O₃ phase. The LFMR is connected with the interface of grain or grain boundary, while the giant magnetoimpedance under low fields for La_0.67Sr_0.33Mn_0.98Co_0.02O₃ sintered plates strongly depends upon the plate thickness. With an increase of sample thickness, the magnetoimpedance increases and the frequency, where the maximum magnetoimpedance occurs, shifts to low frequencies. A giant magnetoimpedance of −15.6% and a large AC magnetoresistance of −30.5% could be obtained under a very small field H = 600 Oe for the plate with a thickness of 3 mm.     

Enthalpy of formation of selected mixed oxides in a CaO-SrO-Bi2O3-Nb2O5 system

The heats of drop-solution in 3Na₂O + 4MoO₃ melt at 973 K and 1073 K for calcium and strontium carbonates, Bi₂O₃, Nb₂O₅ and several stoichiometric mixed oxides in CaO-Nb₂O₅, SrO-Nb₂O₅ and Bi₂O₃-Nb₂O₅ systems were measured using a Setaram Multi HTC-96 calorimeter. The values of enthalpy of formation from constituent binary oxides at 298 K, Δ_oxH, were derived for the mixed oxides under investigation: Δ_oxH(CaNb₂O₆) = −132.0 ± 23.8 kJ mol⁻¹, Δ_oxH(Ca₂Nb₂O₇) = −208.0 ± 31.9 kJ mol⁻¹, Δ_oxH(SrNb₂O₆) = −167.9 ± 19.1 kJ mol⁻¹, Δ_oxH(Sr₂Nb₂O₇) = −289.2 ± 37.5 kJ mol⁻¹ and Δ_oxH(BiNbO₄) = −41.9 ± 11.1 kJ mol⁻¹. Additionally, the values Δ_oxH for other mixed oxides with different stoichiometries were estimated on the basis of these experimental results.     

Mechanical properties of La2O3 doped diamond-like carbon films

Twelve La₂O₃ doped diamond-like carbon (DLC) nanofilms were deposited using unbalanced dual-magnetron sputtering. AFM, XRD, Raman spectroscopy, AES, XPS, TEM, contact surface profiler and nanoindenter were employed to investigate the structure and tribological properties of deposited films. The results show that the La₂O₃ doped DLC films are amorphous. La₂O₃ doping obviously decreases internal stress, and effectively increases the elastic modulus. This results from the dissolving and dissolution of La₂O₃ within the amorphous DLC matrix. Furthermore, the friction coefficient of the doped DLC films decreases, and adhesion strength increases. These are attributed to the lubrication function of La₂O₃ and the formation of transition layer at interface, respectively.     

Synthesis, structure, and properties of Li2Pb2CuB4O10 with isolated [CuB4O10] units

The copper borate Li₂Pb₂CuB₄O₁₀ has been synthesized in air by the standard solid-state reaction at temperature in the range 550-650 °C and the structure of Li₂Pb₂CuB₄O₁₀ was determined by single-crystal X-ray diffraction. Li₂Pb₂CuB₄O₁₀ crystallizes in the monoclinic space group C2/c (no. 15) with a = 16.8419(12), b = 4.7895(4), c = 13.8976(10) Å, and β = 125.3620(10)°, V = 914.22(12) Å³, and Z = 4, as determined by single-crystal X-ray diffraction. The Li₂Pb₂CuB₄O₁₀ structure exhibits isolated units of stoichiometry [CuB₄O₁₀]⁶⁻ that are built from CuO₄ distorted square planes and triangular BO₃ groups. The IR spectroscopy and thermal analysis investigations of Li₂Pb₂CuB₄O₁₀ are also presented.     

Sol-gel synthesis of Bi3.25La0.75Ti3O12 nanotubes

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) nanotubes were synthesized by sol-gel technique using nanochannel porous anodic aluminum oxide (AAO) templates, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). BLT nanotubes with diameter of around 240 nm and the wall thickness of about 25 nm exhibited a single orthorhombic perovskite structure and highly preferential crystal growth along the [1 1 7] orientation, which have smooth wall morphologies and well-defined diameters corresponding to the diameter of the applied template. The formation mechanism of BLT nanotubes was discussed.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.