Sol–gel synthesis of 2D and 3D nanostructured YSZ:Yb<Superscript>3+</Superscript> ceramics

This paper presents results of a detailed study of fundamental aspects of the formation of 2D and 3D nanostructured YSZ:Yb³⁺ ceramics with a cubic structure through a key synthesis step in aqueous solutions of zirconium-containing hydroxy nanoparticles (1–2 nm) modified by Y³⁺ and Yb³⁺ ions, with the use of a sol–gel method and subsequent calcination of the resultant xerogels at temperatures above 350°C. As starting chemicals for the synthesis of ceramic powders, we used zirconyl, yttrium, and ytterbium nitrates and chlorides and aqueous ammonia. Using mixed solutions of these salts and a procedure developed by us, we synthesized sols, gels, and xerogels. To examine the effect of temperature on solid-state transformations, the xerogels were calcined according to a predetermined program in a muffle furnace at temperatures in the range from 350 to 1350°C (rarely, up to 1650°C). We focused primarily on ceramic powders close in composition to 0.86ZrO₂ · 0.10Y₂O₃ · 0.04Yb₂O₃. The ceramics were characterized by high-resolution transmission electron microscopy, electron microdiffraction, electronic diffuse reflectance spectroscopy, energy dispersive X-ray microanalysis, and X-ray fluorescence analysis.     

Sol–gel combustion synthesis of nanocrystalline LaMnO<Subscript>3</Subscript> powders and photocatalystic properties

A novel LaMnO₃ photocatalyst with perovskite structure was prepared by sol–gel combustion method. The combustion reaction mechanisms of nanocrystalline LaMnO₃ powders were investigated by thermal analysis, infrared spectra, and X-ray diffraction technique. The results showed that the gels exhibited self-propagating behavior after ignition in air. Nanocrystalline LaMnO₃ powders can be synthesized in one step by using sol–gel combustion synthesis. The photocatalytic activity of the LaMnO₃ powders were evaluated by degradation of methyl orange (MO) in water under UV light irradiation. The results showed that the LaMnO₃ powders exhibit good photocatalytic activities under UV light irradiation. The degradation percentage after 36 h on LaMnO₃ powders was about 76%.     

Cathodoluminescence properties of SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript>and ZnO·SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript> phosphor nanopowders

The successful incorporation of ZnO nanoparticles in Pr³⁺-doped SiO₂ using a sol–gel process is reported. SiO₂:Pr³⁺ gels, with or without ZnO nanoparticles, were dried at room temperature and annealed at 600 °C. On the basis of the X-ray Diffraction (XRD) results, the SiO₂ was amorphous regardless of the incorporation of Pr³⁺ and nanocrystalline ZnO or annealing at 600 °C. The particles were mostly spherical and agglomerated as confirmed by Field Emission Scanning Electron Microscopy. Thermogravimetric analysis of dried gels performed in an N₂ atmosphere indicated that stable phases were formed at ≥900 °C. Absorption bands ascribed to ³H₄-³P_{(J = 0,1,2)}, ¹I₆ and ¹D₂ in the UV–VIS region were observed from SiO₂:Pr³⁺ colloids. The red cathodoluminescent (CL) emission corresponding to the ³P₀ → ³H₆ transition of Pr³⁺ was observed at 614 nm from dried and annealed SiO₂:Pr³⁺ powder samples. This emission was increased considerably when ZnO nanoparticles were incorporated. The CL intensity was measured at an accelerating voltage of 1-5 keV and a fixed beam current of 8.5 μA. The effects of accelerating voltage on the CL intensity and the CL degradation of SiO₂:Pr³⁺ and ZnO·SiO₂:Pr³⁺ were also investigated using Auger electron spectroscopy coupled with an Ocean Optics S2000 spectrometer.     

Synthesis and luminescence properties of RMgPO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript> (R = Li,Na, and K) red phosphor

RMgPO₄:Mn²⁺ (R?=?Li, Na, and K) phosphors are synthesized by a solid-state reaction method in air. The crystal structures and luminescence properties are investigated. A broad emission band peaking at 638 nm of RMgPO₄:Mn²⁺ (R?=?Li and Na) phosphors with excitation 408 nm is observed in the range of 550–800 nm owing to the ⁴T₁(G) → ⁶A₁ transition of the Mn²⁺ ion. KMgPO₄:Mn²⁺ phosphor with excitation 416 nm shows a broad emission band peaking at 658 nm in the range of 550–800 nm owing to the ⁴T₁(G) → ⁶A₁ transition of the Mn²⁺ ion. The optimal Mn²⁺ ion concentration in RMgPO₄:Mn²⁺ (R?=?Li, Na, and K) phosphors is about 5 mol%. The lifetimes of RMg_0.95PO₄:0.05Mn²⁺ (R?=?Li, Na, and K) phosphors is ~6.21, 6.03, and 6.28 ms, respectively. The luminous mechanism is explained by Tanabe-Sugano diagram of Mn²⁺ ion.     

Cost-effective electrostatic-sprayed SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2 + </Superscript> phosphor coatings by using salted sol–gel derived solution

3 Mol% of europium doped strontium aluminate (SrAl₂O₄:Eu^2 +) coatings on silicon substrates were prepared by electrostatic spray deposition method using a salted sol–gel derived solution as a starting material. As-deposited films at 100°C for 5 h were heated at 1100°C for 2 h under a reducing ambient atmosphere of 95%N₂ + 5%H₂. Nanocrystalline SrAl₂O₄ film was confirmed by surface morphological and crystallographic analyses. Monitored at 520 nm, the excitation spectrum showed a broad band from 300 ~ 500 nm and the emission intensity showed a maximum yellow peak intensity at 512 nm with a broad band from 460 ~ 610 nm.     

Controllable synthesis and luminescence of YPO<Subscript>4</Subscript>:Ln<Superscript>3+</Superscript> (Ln = Eu and Sm) nanotubes

YPO₄:Ln³⁺ (Ln = Eu and Sm) nanotubes were synthesized by a precipitation process in the presence of SDS. The XRD results showed that all samples have a xenotime type tetragonal structure, indicating that doped rare earth ions have no influence on the phase. The SEM and TEM images showed that all samples are nanotubes. On basis of the morphology of samples and the properties of SDS, the possible formation mechanism was speculated. YPO₄:Eu³⁺ and YPO₄:Sm³⁺ nanotubes showed characteristic emission bands of Eu³⁺ and Sm³⁺ ions, respectively. For YPO₄:Eu³⁺/Sm³⁺ nanotubes, the codoping Sm³⁺ ions can enhance the emission intensity of Eu³⁺ ions.     

Sol–gel synthesis of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> composites from tantalum(V) chloride and tetraethyl orthosilicate in ethanol

Ta₂O₅–SiO₂ composites containing 10, 50, and 90 wt % SiO₂ have been prepared by a sol–gel process in ethanolic solutions of tantalum(V) chloride with tetraethyl orthosilicate. The physicochemical aspects of their formation have been studied by IR spectroscopy, X-ray diffraction, X-ray microanalysis, and thermal analysis in combination with mass spectrometry. The results demonstrate that the SiO₂ content of the Ta₂O₅–SiO₂ composites influences the uniformity of the tantalum and oxygen distributions on the surface of the materials and that heat-treatment conditions influence their crystallinity.     

Effect of Zn<Superscript>2+</Superscript> doping on the structural,magnetic and dielectric properties of MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by the sol–gel method

Mn_1?xZn_xFe₂O₄ (x?=?0.2–0.8) ferrite samples were successfully prepared by the sol–gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn_1?xZn_xFe₂O₄ samples. The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn²⁺ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C for 8 h is found to show the largest M _s value (77.30 emu/g) in this work. These results indicate that Zn²⁺ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn_1?xZn_xFe₂O₄ ferrites.     

Synthesis of Yb<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> co-doped β-NaYF<Subscript>4</Subscript> nanoparticles by sol–gel method and the multi-color upconversion luminescence properties

Well-crystalline β-NaYF₄:Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles were synthesized by sol–gel method using isopropyl alcohol [(CH₃)₂CHOH] as a complexing agent. The samples were characterized by X-ray diffraction, scanning electron microscopic analysis and fluorescence spectrum analysis methods. Under the excitation of 980 nm laser diode (LD), the samples displayed bright upconversion luminescence (UCL), which was generated from the energy level transition of Ho³⁺ and Tm³⁺ ions. With the increase of Tm³⁺, Ho³⁺ and Yb³⁺-doping concentration, the UCL intensity of blue, green and red light emission of the samples varied. Calculation of the CIE color coordinate of the β-NaYF₄:Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles revealed that with the adjustment of Tm³⁺, Ho³⁺ and Yb³⁺ doping concentration and the excitation power of 980 nm LD, the multi-color UCL can be realized. Approximately single red light output with the CIE color coordinate of x?=?0.545, y?=?0.306 and white light output with the CIE color coordinate of x?=?0.325, y?=?0.320 can be obtained in the synthesized β-NaYF₄: Yb³⁺, Ho³⁺, Tm³⁺ nanoparticles.     

Effect of Zn<Superscript>2+</Superscript>, Ti<Superscript>2+</Superscript> dopants on structural,optical and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoparticles synthesized via non-aqueous sol–gel route

Transition divalent metal cations (Zn²⁺, Ti²⁺) doped V₂O₅ nanoparticles were synthesized via non-aqueous sol–gel route. The influence of dopant materials on the characteristics of V₂O₅ nanoparticles was studied. XRD studies ensure that all the prepared samples possess phase pure orthorhombic structure. From the FESEM images, it was noted that the products possess uniform particle size around 20–30 nm. The presence of functional groups and dopants was confirmed by FTIR, Raman, and elemental analysis respectively. From UV–Vis spectra, the significant blue shift was observed for doped samples compared to pure V₂O₅ nanoparticles, which is attributed to the quantum confinement effect. The high capacity retention of the intercalation compound was measured by using C–V study and implies that the prepared samples are very promising electrode materials for supercapacitor.     

Lewis and Brønsted acids in super-acid catalyst SO<Subscript>4</Subscript><Superscript>2−</Superscript>/ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>

Super-acid catalyst, SO₄ ^2?/ZrO₂–SiO₂, with high zirconium loading was synthesized and the nature of the surface acid was investigated by FT-IR of pyridine adsorption. With the increasing ZrO₂ content, the Lewis and Brønsted acid sites increased and reached the maximum when Zr/Si (molar ratio) = 1.3. The sample with Zr/Si = 1.3 showed the strongest IR adsorption band in the S=O stretching region (1,300–1,400 cm^?1). Pyrosulfate and monosulfate species existed on the surface of the catalysts and the acidic strength could be enhanced by induction effect of their S=O groups. And there were two kinds of Brønsted acid sites on the surface of the catalysts.     

<Superscript>210</Superscript>Ро in black and green teas

The ²¹⁰Ро content in various grades of tea sold in St. Petersburg shops was determined, and the effective annual dose of internal irradiation from ²¹⁰Ро at daily tea drinking was estimated. As shown by α-ray spectrometry, the activity concentration of ²¹⁰Ро in tea leaves varies from 1.1 to 25 Bq kg^–1. The ²¹⁰Po content in black teas is, on the average, 1.7 times higher than in green teas. This difference is accounted for by specific features of processes for the production of black and green teas. From 1.5 to 56% of ²¹⁰Ро passes into aqueous extracts. Despite higher polonium content in black teas, the amount of ²¹⁰Po extracted from green teas is, on the average, 6.3 times higher than that extracted from black teas. This effect may be associated with the formation of water-soluble organic polonium compounds on the surface of tea leaves in the course of tea processing. The effective annual dose of internal irradiation from polonium at daily use of 10 g of dry tea is estimated at 0.8–9.5 μSv year^–1 depending on the tea grade, or 0.5–5.8% of the average annual dose of irradiation of the Russian Federation population from the sum of the nuclides (²¹⁰Pb, ²¹⁰Po, ²²⁸Rа, ²²⁶Rа, etc., except ⁴⁰K) getting into a human body with food and water.     

Photoluminescence and thermal stability of yellow-emitting Sr-α-SiAlON:Eu<Superscript>2+</Superscript> phosphor

Novel α-SiAlON:Eu²⁺-based yellow oxynitride phosphors with the formula Sr_0.375−x Eu _x ²⁺Si_12−m−n Al _m+n O _n N_16−n (m = 0.75, n = x = 0.004–0.04) have been prepared by firing the powder mixture of SrSi₂, α-Si₃N₄, AlN, and Eu₂O₃ at 2,000 °C for 2 h under 1 MPa nitrogen atmosphere. The luminescence properties, the dependence of the activator concentration of Eu²⁺ and the thermal stability of Sr-α-SiAlON:Eu²⁺ phosphor have been investigated in comparison with Ca-α-SiAlON:Eu²⁺ phosphor. Similar to Ca-α-SiAlON:Eu²⁺ phosphor, Sr-α-SiAlON:Eu²⁺ phosphor has the excitation wavelength ranging from the ultraviolet region to 500 nm, and exhibit intense yellow light. The strongest luminescence was achieved at about x = 0.02 with the emission peak at 578 nm, slightly shorter than that of Ca-α-SiAlON:Eu²⁺ phosphor at 581 nm. Temperature-dependent emission intensity of Sr-α-SiAlON:Eu²⁺ phosphor is comparable to that of Ca-α-SiAlON:Eu²⁺ phosphor. The results suggest that the different position of the emission peak for Sr- and Ca-α-SiAlON:Eu²⁺ depends on the composition and the Stokes shift, and the thermal stability is nearly independent of Sr and Ca or fixed by the network of (Si, Al)–(O, N) in α-SiAlON at the same Eu²⁺ concentration.     

The role of Sr<Superscript>2+</Superscript> on the structure and reactivity of SrO–CaO–ZnO–SiO<Subscript>2</Subscript> ionomer glasses

The suitability of Glass Polyalkenoate Cements (GPCs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. To further improve their potential, and given that Strontium (Sr) based drugs have had success in the treatment of osteoporosis, the authors have substituted Calcium (Ca) with Sr in the glass phase of a series of aluminium free GPCs. However to date little data exists on the effect SrO has on the structure and reactivity of SrO–CaO–ZnO–SiO₂ glasses. The objective of this work was to characterise the effect of the Ca/Sr substitution on the structure of such glasses, and evaluate the subsequent reactivity of these glasses with an aqueous solution of Polyacrylic acid (PAA). To this end ²⁹Si MAS-NMR, differential scanning calorimetry (DSC), X-ray diffraction, and network connectivity calculations, were used to characterize the structure of four strontium calcium zinc silicate glasses. Following glass characterization, GPCs were produced from each glass using a 40 wt% solution of PAA (powder:liquid = 2:1.5). The working times and setting times of the GPCs were recorded as per International standard ISO9917. The results acquired as part of this research indicate that the substitution of Ca for Sr in the glasses examined did not appear to significantly affect the structure of the glasses investigated. However it was noted that increasing the amount of Ca substituted for Sr did result in a concomitant increase in setting times, a feature that may be attributable to the higher basicity of SrO over CaO.     

Effect of additional Zn<Superscript>2+</Superscript> dopant on the ferromagnetic properties of Co-doped CeO<Subscript>2</Subscript> nanoparticles prepared by sol–gel method

Effect of additional Zn²⁺ dopant on the ferromagnetism (FM) of Co doped CeO₂ nanoparticles was studied. The Zn and Co co-doped CeO₂ nanoparticles (Ce_0.97?xZn _x Co_0.03O₂: where x?=?0, 0.01, 0.03, 0.05) were prepared by sol–gel technique. The crystal structure, morphology, and magnetic properties were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (Raman) and physical property measurement system (PPMS). XRD and Raman studied showed that certain amount of Zn²⁺ can readily be incorporated into the lattice of Co doped CeO₂ with single-phase of CeO₂ original cubic fluorite crystal structure, and no ferromagnetic secondary phase was observed. SEM images show Zn and Co co-doped CeO₂ nanoparticles were spherical and uniform size. The PPMS studied indicate that the room-temperature FM of Co doped CeO₂ nanoparticles increase with additional Zn²⁺ dopant. This result is helpful in understanding the origin of FM in diluted magnetic oxides (DMO) as well as improving the magnetic property of DMO.     

Sol–gel preparation and luminescence of RE<Subscript>3</Subscript>BO<Subscript>6</Subscript>: Dy<Superscript>3+</Superscript> (RE = La,Y, Gd) microparticles with hybrid precursors

Dysprosium ion activated RE₃BO₆ (RE = La, Y, Gd) polycrystalline phosphors have been prepared via a modified sol–gel process with urea as fuel and rare earth nitrates as precursors. The crystal phase and the morphology of the phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average particle size after heat treatment at 1,000 °C is around 5 μm by particle size determination technique. The characteristic transitions of Dy³⁺ due to ⁴F_9/2 → ⁶H_15/2 (blue) and ⁴F_9/2. → ⁶H_13/2 (yellow) can be observed in the emission spectra and the yellow-to-blue intensity ratio (Y/B) can be changed with the variety of the doped concentration of Dy³⁺ ion. Zeta potential shows the relationship between the surface charges to the pH value in suspension.     

Role of Mg<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, and F<Superscript>–</Superscript> ions in octacalcium phosphate crystallization

We have synthesized octacalcium phosphate (OCP) in the presence of inorganic additives (magnesium, strontium, and fluoride ions) and studied the composition, morphology, thermal stability, and dynamic dissolution of the samples thus obtained. It has been shown that, in addition to OCP, magnesium and strontium ions favor the formation of brushite and hydroxyapatite (HA), whereas fluoride ions favor the formation of HA and fluorohydroxyapatite (FHA). We have proposed a process for the preparation of powder materials whose resorption kinetics in corrosive liquid media are corrected by adding dopants capable of activating the dissolution process.     

Synthesis and luminescent properties of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript> blue–green emitting phosphor for white light-emitting diodes (LEDs)

An efficient blue–green emitting phosphor, Sr₄Al₁₄O₂₅:Eu²⁺, was prepared by solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Sr₄Al₁₄O₂₅:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 8–10 μm. Photoluminescence measurements showed a broad absorption band between 300 and 450 nm which was efficiently excited by near-ultraviolet (NUV) LEDs (350–410 nm) and a strong emission band peaking at 491 nm. A bright blue–green LED with chromatic coordination (0.176, 0.412) was fabricated by incorporating the phosphor with an InGaN-based NUV chip, which indicates that Sr₄Al₁₄O₂₅:Eu²⁺ is a good candidate phosphor for application in white LEDs.     

Geometric and Disorder-Type Magnetic Frustration in Ferrimagnetic “114” Ferrites: Role of Diamagnetic Li<Superscript>+</Superscript> and Zn<Superscript>2+</Superscript> Cation Substitution

The comparative study of the substitution of zinc and lithium for iron in the “114” ferrites, YBaFe₄O₇ and CaBaFe₄O₇, shows that these diamagnetic cations play a major role in tuning the competition between ferrimagnetism and magnetic frustration in these oxides. The substitution of Li or Zn for Fe in the cubic phase YBaFe₄O₇ leads to a structural transition to a hexagonal phase YBaFe_4−x M _x O₇, for M = Li (0.30≤x≤0.75) and for M = Zn (0.40≤x≤1.50). It is seen that for low doping values, i.e. x=0.30 (for Li) and x=0.40 (for Zn), these diamagnetic cations induce a strong ferrimagnetic component in the samples, in contrast to the spin-glass behavior of the cubic phase. In all the hexagonal phases, YBaFe_4−x M _x O₇ and CaBaFe_4−x M _x O₇ with M = Li and Zn, it is seen that in the low-doping regime (x∼0.3 to 0.5), the competition between ferrimagnetism and 2D magnetic frustration is dominated by the average valency of iron. In contrast, in the high-doping regime (x∼1.5), the emergence of a spin glass is controlled by the high degree of cationic disorder, irrespective of the iron valency.     

Syntheses and proton conductivity of mesoporous Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> and NdOCl–SiO<Subscript>2</Subscript> composites

Two mesoporous oxide composites of Nd₂O₃–SiO₂ and NdOCl–SiO₂ were synthesized using SBA-15 as a template and neodymium nitrate or neodymium chloride as a precursor. The porous Nd₂O₃–SiO₂ with a SBA-15-like structure has amorphous walls and the porous NdOCl–SiO₂ with a replicated structure of SBA-15 has crystalline walls. These porous materials were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption. They exhibited significant proton conductivities in the presence of moisture at low temperatures and the highest conductivity observed was 4.55 × 10⁻⁴ S/cm at 47 °C in wet air (RH = 28.6%).