Synthesis and photoluminescence of the Y2O3:Eu3+ phosphor nanowires in AAO template

The monodisperse array and nanowires of Y₂O₃:Eu³⁺ phosphor were synthesized using anodic aluminum oxide (AAO) template by sol–gel method. Scanning electron microscope (SEM) images indicated that Y₂O₃:Eu³⁺ nanowires are parallelly arranged, all of which are in uniform diameter of about 50 nm. The high-magnification SEM image showed that each nanowire is composed of a lot of agglutinating particles. The patterns of selected-area electron diffraction confirmed that Y₂O₃:Eu³⁺ nanowires mainly consist of polycrystalline materials. Excitation and emission spectra of Y₂O₃:Eu³⁺/AAO composite films were measured. The characteristic red emission peak of Eu³⁺ ion attributed to ⁵D₀→⁷F₂ transition in Y₂O₃:Eu³⁺/AAO nanowires broadened its halfwidth.     

MgAl2O4:Eu3+ nanoplates and nanoparticles as red-emitting phosphors: Shape-controlled synthesis and photoluminescent properties

We demonstrate herein a facile hydrothermal synthesis followed by post-annealing approach to selectively prepare MgAl₂O₄:Eu³⁺ nanoplates and nanoparticles. Series of scientific techniques such as XRPD, FESEM, TEM, HRTEM, and PL were adopted to characterize the as-prepared MgAl₂O₄:Eu³⁺ phosphors. First, by altering the amount of hexamethylenetetramine (abbr. HMTA) in solution, MgAl₂O₄:Eu³⁺ nanoplates occurred. Next, MgAl₂O₄:Eu³⁺ nanoparticles were prepared by adding certain amounts of sodium citrate and sodium dodecylbenzenesulfonate (abbr. SDBS). In particular, the MgAl₂O₄:Eu³⁺ nanoplates have novel porous structures. Besides, the MgAl₂O₄:Eu³⁺ phosphors exhibit excellent red-emitting properties based upon the characteristic transitions of Eu³⁺ from ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, and 4).     

Synthesis and optical properties of novel red phosphors YNbTiO6:Eu3+ with highly enhanced brightness by Li+ doping

Highly luminescent euxenite phased YNbTiO₆:Eu³⁺ and Li⁺-doped YNbTiO₆:Eu³⁺ red phosphors have been prepared through a facile sol–gel combustion process and investigated for the first time. The introduction of Li⁺ ions into YNbTiO₆:Eu³⁺ is able to result in significant changes of the crystallinity and particle size, and bring a clear red-shift of absorption edge. A dominant red emission peak at 611 nm due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ was observed from photoluminescence spectra of the YNbTiO₆:Eu³⁺ and Li⁺-doped YNbTiO₆:Eu³⁺ phosphors. In particular, the emission intensity of the optimal Li⁺-doped YNbTiO₆:Eu³⁺ was examined to be close to 400% of commercial Y₂O₃:Eu³⁺ phosphor. The mechanism of the enhanced emission by Li⁺ doping was discussed.     

Vacuum ultraviolet spectroscopic properties of rare earth (RE) (RE = Eu,Tb, Dy,Sm, Tm)-doped K2GdZr(PO4)3 phosphate

The luminescent characteristics of RE (RE³⁺ = Eu, Tb, Dy, Sm and Tm)-doped K₂GdZr(PO₄)₃ have been investigated. The band in the range of 130–157 nm in the VUV excitation spectra of these compounds is attributed to the host lattice or PO₄^3? group absorption and the band from 157 nm to 215 nm with the maximum at 188 nm is due to the O–Zr charge transfer transition. For Eu³⁺-doped sample, the relatively weak band of O^2?–Eu³⁺ charge transfer (CTB) at 222 nm is observed and for Tb³⁺-doped sample, the band at 223 nm is related to the 4f–5d spin-allowed transition of Tb³⁺. For Dy³⁺- and Sm³⁺-doped samples, the O^2?–Dy³⁺ and O^2?–Sm³⁺ CTBs have not been observed, probably due to the 2p electrons of oxygen tightly bound to the zirconium ion in the host lattice. In Tm³⁺-doped sample, the weak O^2?–Tm³⁺ CTB is located at 170 nm. It is observed that there is energy transfer between the host and the luminescent activators (e.g. Eu³⁺, Tb³⁺ and Sm³⁺) except for Tm³⁺.     

Y2O3:Eu (5 mol%) with Ag nanoparticles prepared by citrate precursor

Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) and Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) containing 1 mol% of Ag nanoparticles were prepared by heat treatment of a viscous resin obtained via citrate precursor. TEM and EDS analyses showed that Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) is formed by nanoparticles with an average size of 12 nm, which increases to 30 nm when Ag is present because the effect of metal induced crystallization occurs. Ag nanoparticles with a size of 9 nm dispersed in Y₂O₃:Eu³⁺ (5 mol% Eu³⁺) were obtained and the surface plasmon effect on Ag nanoparticles was observed. The emission around 612 nm assigned to the Eu³⁺ (⁵D₀→⁷F₂) transition enhanced when the Ag nanoparticles were present in the Y₂O₃:Eu³⁺ luminescent material.     

A Eu/Gd-mixed metal-organic framework for ultrasensitive physiological temperature sensing

A stable and biocompatible MOF-based thermometer utilizing back energy transfer has been developed, which exhibits ultrasensitive temperature sensing performance in the physiological temperature range.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Substitution of Sr2+ by Eu3+ in Bi-2201 ceramics,effects on structure and physical properties

In this paper, we report the effects of the substitution of Sr by Eu on the properties of Bi-2201 ceramics. Samples with nominal compositions of Bi₂Sr_2?xEu_xCuO_y (x = 0–0.4) are elaborated in air by solid state reaction. They are characterized by means of X ray diffraction (XRD), scanning electron microscopy (SEM), magnetic and resistivity measurements. The undoped sample (x = 0) is monophasic and its structure belongs to phase A. No trace of superconductivity is observed down to 2 K for this sample and the variation of resistivity with temperature shows a semiconducting behaviour. As Eu is added and for x ≥ 0.2, the samples convert totally to B or Raveau phase and become superconducting. The highest T_c, obtained from both magnetic and resistivity measurements, is observed for x = 0.3. In the normal state, all the samples exhibit a semiconducting character which decreases as well as resistivity when the Eu content increases. The refinement of cell parameters is done with considering the structural modulation. The study shows that the substitution of Sr²⁺ by Eu³⁺ leads to an increase of a and b parameters, while c decreases similarly to those of the La doped phases. The a axis component of the modulation is observed to be independent of Eu content, while the c axis one increases slightly as this content increases. The XRD analysis has also revealed that the limit solubility of the used Eu₂O₃ oxide is situated between x = 0.3 and 0.4 of Eu content. The SEM micrographs show that the undoped sample consists of poorly connected grains with a random distribution. A quite different microstructure is obtained for the doped samples. The grains are more connected and have a flat shape which is characteristic of the Bi-based superconductors.     

Improved luminescent behavior of YVO4:Eu3+ ceramic phosphors by Li contents

Crystalline phase and surface morphology of phosphors are important factors to determine luminescent characteristics. Li-doped YVO₄:Eu³⁺ ceramic samples were prepared by a solid state reaction method. The Li⁺ concentration was varied from 1 to 3 wt% to improve crystallinity and surface morphology of ceramics. Influence of Li doping on luminescent properties of YVO₄:Eu³⁺ ceramics has been investigated. Photoluminescence spectra have been measured at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet light source with an excitation wavelength of 325 nm. The emitted radiation was dominated by a red emission peak at 620 nm radiated from the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. As Li⁺ ion content increases from 0 to 2 wt%, the photoluminescence (PL) brightness improved. The brightness of 2 wt% Li-doped YVO₄:Eu³⁺ ceramic was increased by a factor of 1.43 in comparison with that of YVO₄:Eu³⁺ ceramic. The enhanced luminescence resulted not only from the improved crystallinity but also from the enhanced surface roughness. The luminescent intensity and surface roughness exhibited similar behavior as a function of Li⁺ ion concentration.     

Luminescence and dielectric properties of nano-structured Eu3+:K2O–Nb2O5–SiO2 glass-ceramics

In the present study, results concerning luminescence and dielectric properties of Eu₂O₃ (0.5 wt% in excess) doped nano-crystallized KNbO₃ containing transparent glass-ceramics obtained from glass of composition 25K₂O–25Nb₂O₅–50SiO₂ (mol%) by varied heat-treatment duration at 800 °C have been analyzed and reported. The formed crystallization phase, crystallite size and morphology have been examined through XRD, FESEM, TEM and FTIRRS measurements. The observed steep increase in the dielectric constant (?) of glass-ceramics over the as-prepared glass is attributed to the formation of ferroelectric nano-crystalline KNbO₃ in glass matrix. The absorption spectra of all the samples have revealed the characteristic 4f–4f intraband absorption transitions of Eu³⁺ ions. The measured photoluminescence spectra have exhibited emission transitions ⁵D_{0, 1} → ⁷F_j (j = 0, 1, 2, 3 and 4) of Eu³⁺ ions. The excited level lifetimes have been determined from measured fluorescence decay curves. The rare earth ion site symmetry (nearly C_v) has been understood based on the nature of the Stark splittings of emission bands detected in both Eu³⁺: glass and Eu³⁺: glass-ceramics.     

Preparation and characterization of NiO(core)/Fe2O3(shell) composite particles

A novel hydrothermal coating process has been developed to deposit amorphous Ni(OH)₂·H₂O over octahedral α-Fe₂O₃ particles by treating aqueous dispersion of the preformed cores in Ni(NO₃)₂/CH₃COONa solution. NiO_(core)/Fe₂O_3(shell) composite particles were prepared by air sintering of the Ni(OH)₂·H₂O_(shell)/Fe₂O_3(core) particles at 200–500°C for 1–6 h. The changes of morphology, structure and weight of the hydrothermal and sintering products were studied by means of TEM, XRD, XPS, TG and IR analyzers. The nucleation and growth model was suggested for the non-isothermal decomposition of Ni(OH)₂·H₂O coatings and the kinetic equation was derived from the non-linear regression of the TG data. The activation in the thermal-decomposition process is 73.8 kJ mol⁻¹ and the pre-exponential factor is 1.95×10⁴ s⁻¹.     

Influence of the RE2O3 (RE = Y,Gd) and CaO nanoadditives on the electromagnetic properties of nanocrystalline Co0.2Ni0.3Zn0.5Fe2O4

The present work reports the influence of the nanoadditives Y₂O₃, Gd₂O₃, and CaO on the magnetic, electrical and dielectric properties of sintered nanoferrites Co_0.2Ni_0.3Zn_0.5Fe₂O₄. All powders were synthesized via the polyol method. XRD analysis showed that except the nanoferrite which was obtained by in an one-post procedure, subsequent calcinations of the as-produced additives were necessary to obtain nanocrystals of the desired phases. The mean particle size inferred from TEM images of the nanoadditives sintered at 1000 °C ranges from 87 nm for Y₂O₃ to 126 nm for CaO. IR spectroscopy provided useful information on the nature of the core and the surface chemistry of the as-produced additives and their associated annealed powders. Upon sintering, it was found that the incorporation of 5 wt.% additives remarkably increased the densification of the doped materials. The most important increase in densification was observed with CaO due to its larger particles. dc M-H hysteresis loops taken at 300 K revealed a superparamagnetic behavior of the produced ferrite/nanoadditives. Additionally, as expected, the ferrite/nanoadditives showed reasonable saturation magnetization and high Curie temperature. The electrical and dielectric properties, namely the resistivity, the loss factor, and the relation frequency were found to be clearly affected by doping. The resistivity decreased with increasing temperature indicating a semiconducting behavior. Further, at room temperature, the highest resistivity was observed with Y₂O₃. The major role was attributed to the high fraction of insulating Y₂O₃ owing to its smallest particles combined with the low Fe²⁺ concentration in the ferrite nanoparticles taking advantages of the moderate sintering temperature. In addition, the dc conductivity was found to follow the Arrhenius law with a slope change observed at the Curie temperature. Further, all the additives clearly affected the ac conductivities of the pure ferrite. The variation of the dielectric permittivity with frequency and temperature was explained on the basis of M-W type of interfacial polarization. Additionally, at high frequencies, the lower dielectric loss was found with Y₂O₃ doping. It was found to be of about 10 times lower than the undoped material and much larger than reported for similar undoped bulk ferrites.     

Embedding of Al nanoparticle in Al2O3 matrix by electron beam

Embedding structures of a metal nanoparticle in an oxide matrix were first achieved by electron beam irradiation. In the system of Al/α-Al₂O₃. Al nanoparticles derived from θ-Al₂O₃ migrated and embedded in α-Al₂O₃ matrix having epitaxy relation, {1 1 2̄ 0}α-Al₂O₃//{2 0 0} Al. The driving force of the embedding is momentum transfer from electrons or ions to Al atoms of nanoparticles in the pole piece of transmission electron microscopy.     

Enhanced frequency upconversion of Sm3+ ions by elliptical Au nanoparticles in dichroic Sm3+: Au-antimony glass nanocomposites

Dichroic Sm³⁺: Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K₂O–B₂O₃–Sb₂O₃ (KBS) by a single-step melt-quench technique involving selective thermochemical reduction. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results indicate that Au⁰ nanoparticles are grown along the (2 0 0) plane direction. The transmission electron microscopic (TEM) image reveals the elliptical Au⁰ nanoparticles having major axis range 12–17 nm. Dichroic behavior is due to elliptical shape of Au⁰ nanoparticles of aspect ratio ～1.2. Au⁰ NPs of concentration of 0.03 wt% (4.1 × 10¹⁸ atoms/cm³) drastically enhances the intensity (～7-folds) of electric dipole ⁴G_5/2 → ⁶H_9/2 red transition (636 nm) of Sm³⁺ ions and then attenuates with further increase in Au⁰ concentration. The magnetic dipole ⁴G_5/2 → ⁶H_5/2 green (566 nm) and ⁴G_5/2 → ⁶H_7/2 orange (602 nm) transitions remain almost unaffected by presence of nano Au⁰. Local field enhancement (LFE) induced by Au⁰ SPR and energy transfer (ET) from fluorescent Au⁰ → Sm³⁺ ions are found to be responsible for the enhancement while reverse ET from Sm³⁺ → Au⁰ and optical re-absorption due to Au⁰ SPR for attenuation.     

Iron (III) nanocomposites for enzyme-less biomimetic cathode: A promising material for use in biofuel cells

In this paper, we discuss the synthesis and electrochemical properties of a new material based on iron oxide nanoparticles stabilized with poly(diallyldimethylammonium chloride) (PDAC); this material can be used as a biomimetic cathode material for the reduction of H₂O₂ in biofuel cells. A metastable phase of iron oxide and iron hydroxide nanoparticles (PDAC–FeOOH/Fe₂O₃-NPs) was synthesized through a single procedure. On the basis of the Stokes–Einstein equation, colloidal particles (diameter: 20 nm) diffused at a considerably slow rate (D = 0.9 × 10^? 11 m s^? 1) as compared to conventional molecular redox systems. The quasi-reversible electrochemical process was attributed to the oxidation and reduction of Fe³⁺/Fe²⁺ from PDAC–FeOOH/Fe₂O₃-NPs; in a manner similar to redox enzymes, it acted as a pseudo-prosthetic group. Further, PDAC–FeOOH/Fe₂O₃-NPs was observed to have high electrocatalytic activity for H₂O₂ reduction along with a significant overpotential shift, ΔE = 0.68 V from ? 0.29 to 0.39 V, in the presence and absence of PDAC–FeOOH/Fe₂O₃-NPs. The abovementioned iron oxide nanoparticles are very promising as candidates for further research on biomimetic biofuel cells, suggesting two applications: the preparation of modified electrodes for direct use as cathodes and use as a supporting electrolyte together with H₂O₂.     

Chrysanthemum-like Co3O4 architectures: Hydrothermal synthesis and lithium storage performances

Three-dimensional chrysanthemum-like Co₃O₄ was prepared via a facile hydrothermal route without any template, and a subsequent calcination process. With a controlled concentration of the homogeneous precipitation agent, urea, a chrysanthemum-like precursor was hydrothermally obtained at 120 °C for 20 h, and the morphology was kept for Co₃O₄ after a subsequent calcination at 300 °C for 2 h. Co₃O₄ chrysanthemum-like architectures are assemblies of nanorods radiating from a common centre, and the nanorods consisted of interconnected nanoparticles with the size of about 30 nm. When tested as an anode material of Li-ion batteries, chrysanthemum-like Co₃O₄ presented a discharge capacity of ∼450 mA h/g after 50 discharge/charge cycles.     

Synthesis,characterizations of silica-coated gold nanorods and its applications in electroanalysis of hemoglobin

Gold nanorods (GNRs) were synthesized by a seed–mediated growth approach followed by TEOS polymerization leading to the formation of silica layer surrounding the gold nanorod core. TEM images showed that the silica-coated gold nanorods (GNRs@SiO₂) were dispersed with an average aspect ratio of 3.1 for the GNRs cores and a uniform thickness of the silica shell. The core/shell nanocomposites were further used as efficient supports for the immobilization of hemoglobin (Hb) to fabricate a novel biosensor. The immobilized Hb showed an enhanced electron transfer for its heme Fe(III) to Fe(II) redox couple. This biosensor showed an excellent bioelectrocatalytic activity towards H₂O₂ with a linear range from 8.0 × 10⁻⁷ to 6.1 × 10⁻⁵ M, and the detection limit was 6.0 × 10⁻⁸ M at 3σ. The apparent Michaelis–Menten constant of the immobilized hemoglobin was calculated to be 0.13 mM.     

Mesoporous TiO2 nano networks: Anode for high power lithium battery applications

Anatase phase mesoporous TiO₂ with I41/amd space group was synthesized via the urea assisted hydrothermal method. The existence of mono phasic TiO₂ sub-microspheres of uniform particle size (ca. 400 nm) encompassing an average crystallite size of 14 nm was demonstrated using the XRD, FE-SEM and TEM analysis. Surface area of ca. 116.49 m²/g along with a pore size of 7 nm was calculated using the BET and adsorption isotherm measurements which authenticated the mesoporous nature of the synthesized material. Suitable calcination temperature for the better electrochemical property was established via the optimization process. Accordingly, the mesoporous TiO₂ calcined at 400 °C displayed improved cycleability with excellent rate capability ever reported, even at 20 C-rate of discharge. The reason for the superior rate capability is corroborated to the highly mesoporous nature of the TiO₂ sub-microspheres that has imparted desirable surface area apposite for enhanced ionic and electronic diffusion.     

Selected‐Control Fabrication of Multifunctional Fluorescent–Magnetic Core–Shell and Yolk–Shell Hybrid Nanostructures

The selected‐control preparation of uniform core–shell and yolk–shell architectures, which combine the multiple functions of a superparamagnetic iron oxide (SPIO) core and europium‐doped yttrium oxide (Y₂O₃:Eu) shell in a single material with tunable fluorescence and magnetic properties, has been successfully achieved by controlling the heat‐treatment conditions. Furthermore, the shell thickness and interior cavity of SPIO@Y₂O₃:Eu core–shell and yolk–shell nanostructures can be precisely tuned. Importantly, as‐prepared SPIO@Y₂O₃:Eu yolk–shell nanocapsules (NCs) modified with amino groups as cancer‐cell fluorescence imaging agents are also demonstrated. To the best of our knowledge, this is the first report on the selected‐control fabrication of uniform SPIO@Y₂O₃:Eu core–shell nanoparticles and yolk–shell NCs. The combined magnetic manipulation and optical monitoring of magnetic–fluorescent SPIO@Y₂O₃:Eu yolk–shell NCs will open up many exciting opportunities in dual imaging for targeted delivery and thermal therapy.     

The enthalpies of formation of BaCe1−xRExO3−δ (RE = Eu,Tb, Gd)

The preparation of BaCeO₃ doped by gadolinium, europium, and terbium oxides (BaCe_0.8Eu_0.1Tb_0.1O_2.9 and BaCe_0.8Gd_0.2O_2.9) has been performed by solid-state reaction from BaCO₃, CeO₂, Gd₂O₃, Eu₂O₃, Tb₄O₇. The X-ray measurements have showed that BaCe_0.8RE_0.2O_2.9 (RE = Gd, Eu, Tb) was orthorhombic structure (space group Pnma). The standard formation enthalpies of BaCe_0.8Eu_0.1Tb_0.1O_2.9 and BaCe_0.8Gd_0.2O_2.9 have been determined by solution calorimetry combining the solution enthalpies of BaCe_0.8Gd_0.2O_2.9 (BaCe_0.8Eu_0.1Tb_0.1O_2.9) and BaCl₂ + 0.8CeCl₃ + 0.2GdCl₃ (BaCl₂ + 0.8CeCl₃ + 0.1EuCl₃ + 0.1TbCl₃) mixtures in 1 M HCl with 0.1 M KI at T = 298.15 K and literature data.