Characterization of Fe<Superscript>3+</Superscript>-doped silver phosphate glasses

The relationship among the composition, structure and selected properties for five series of silver phosphate glasses containing 0, 5, 10, 15 and 20 wt% Fe₂O₃ has been investigated. The synthesized glasses have been characterized using different experimental techniques. X-ray diffraction studies revealed that the glasses are amorphous in nature. IR spectral studies have shown the presence of characteristic P–O–P linkages of linear phosphate chains, presence of O–P–O units in the phosphate tetrahedral and the formation of P–O–Fe bonds in the doped glass. It is also confirmed that due to doping of Fe₂O₃, loosening of glassy structure occurred and the glass became more disordered. Differential scanning calorimetric (DSC) studies revealed that glass transition temperature increased with Fe₂O₃ concentration. Scanning electron microscopic studies have shown that Fe₂O₃ doping modifies the microstructures of the glass and at lower concentration of dopant, a nanostructure is obtained. Electrical conductivity measurements from 303 to 373 K in a frequency range from 100 Hz to 5 MHz have indicated that all glasses are ionic conductors with Ag⁺ ions as the charge carrier. Fe₂O₃ doping in silver phosphate glass increased the electrical conductivities. Results have shown that dielectric constants increased with the increase of temperature at all the frequencies; a.c. and d.c. conductivities have been separated and a Cole–Cole plot is also drawn. Dielectric losses in all the glasses decreased with frequency at a particular temperature. It is found that Ag₂O–P₂O₅ glass doped with 5 wt% Fe₂O₃ gives high OCV value and the doped glass can be used as an electrolyte for solid-state batteries.     

Chitosan-encapsulated ZnS : M (M: Fe<Superscript>3+</Superscript> or Mn<Superscript>2+</Superscript>) quantum dots for fluorescent labelling of sulphate-reducing bacteria

Chitosan-encapsulated Mn²⁺ and Fe³⁺-doped ZnS colloidal quantum dots (QDs) were synthesized using chemical precipitation method. Though there are many reports on bio-imaging applications of ZnS QDs, the present study focussed on the new type of microbial-induced corrosive bacteria known as sulphate-reducing bacteria, Thiobacillus novellus. Sulphate-reducing bacteria can obtain energy by oxidizing organic compounds while reducing sulphates to hydrogen sulphide. This can create a problem in engineering industries. When metals are exposed to sulphate containing water, water and metal interacts and creates a layer of molecular hydrogen on the metal surface. Sulphate-reducing bacteria then oxidize the hydrogen while creating hydrogen sulphide, which contributes to corrosion for instance, in pipelines of oil and gas industries. In this study, detection and labelling of sulphate-reducing bacteria is demonstrated using fluorescent QDs. Chitosan capped ZnS QDs were synthesized using dopants at different doping concentrations. UV–Vis spectroscopy, XRD and FTIR characterizations were done to identify the optical band gap energy, crystal planes and determine the presence of capping agent, respectively. The morphology and the average particle size of 3.5 ± 0.2 nm were analysed using TEM which substantiated UV–Vis and XRD results. Photoluminescence spectroscopy detected the bacteria attachment to the QDs by showing significant blue shift in bacteria conjugated ZnS QDs. Fluorescence microscopy confirmed the fluorescent labelling of QDs to Thiobacillus novellus bacteria cells making them ideal for bio-labelling applications.     

Spectral parameters of Er<Superscript>3+</Superscript> ion in Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The spectral parameters of Er³⁺ in Yb³⁺/Er³⁺:KY(WO₄)₂ crystal with space group C2/c have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters are: ₂ = 6.33 × 10^–20 cm², ₄ = 1.35 × 10^–20 cm², ₆ = 1.90 × 10^–20 cm². The radiative lifetime and the fluorescence branch ratios were calculated. The emission cross section _e (at 1536 nm) is 2.0 × 10^–21 cm².     

Synthesis of polyacrylate/polyethylene glycol interpenetrating network hydrogel and its sorption for Fe<Superscript>3+</Superscript> ion

A simple two-step aqueous polymerization method was introduced to synthesize polyacrylate/polyethylene glycol (PAC/PEG) interpenetrating network (IPN) hydrogel. The sorption behaviors and mechanism were studied by the sorption of PAC/PEG IPN hydrogel to Fe³⁺ ion from aqueous solution. The experimental results revealed that the adsoption amount of Fe³⁺ ion using swollen hydrogels was much higher than that using the dried composite, they were 75.69 mg/g and 14.25 mg/g, respectively. The parameters, such as neutralization degree, acrylic acid (AA) dosages and temperature, on the sorption amount of PAC/PEG IPN hydrogel were detailedly investigated.     

Improvement of the Magnetization of Barium Hexaferrites Induced by Substitution of Nd<Superscript>3+</Superscript> Ions for Fe<Superscript>3+</Superscript> Ions

Barium hexagonal ferrites (BaNd _x Fe_12?x O ₁₉) have been synthesized by initial high-energy milling of the precursors and calcining subsequently. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD and SEM examinations reveal that a high-crystallized hexagonal BaNd _x Fe_12?x O ₁₉ with lamellar morphology is obtained when the precursor is calcined at 1200^°C in air for 3 h. The hexagonal crystalline structure of BaFe₁₂ O ₁₉ is not changed after doping Nd³⁺ ions in BaFe₁₂ O ₁₉. However, lattice parameters a and b values increase with an increase in Nd content at first, then decrease. Nd substitution may improve the magnetic properties of BaNd _x Fe_12?x O ₁₉. BaNd_0.1Fe_11.9 O ₁₉, obtained at 1050^°C, has the highest specific saturation magnetization value (80.81 emu/g) and magnetic moment (16.21 μ _B); BaNd_0.2Fe_11.8 O ₁₉, obtained at 950^°C, has the highest coercivity value, 4075.19 Oe.     

Photoluminescence and dielectric properties of Eu<Superscript>3+</Superscript> substituted microwave ceramics

Ln_0.9Eu_0.1TiNbO₆ (Ln = Pr, Nd, Sm, Dy and Y) ceramics have been prepared through the solid state ceramic route. The samples are calcined at about 1,250 °C and sintered between 1,370 and 1,425 °C for 4 hours. Structure of the samples is analyzed using X-ray diffraction method. Pr, Nd, Sm and Y based compounds form solid solutions while Dy based compound is a composite. The microstructure is analyzed using Scanning Electron Microscopy. All the compositions have strong photoluminescence in the visible region. The dielectric constant (ε _r ), the unloaded quality factor (Q _u ) and the temperature coefficient of resonant frequency (τ _f ) are measured in the microwave frequency region. The samples have relatively high ε _r , high Q _u  × f and good thermal stability. Hence these materials are suitable for optoelectronic and dielectric resonator applications.     

Flavonoid moiety-incorporated carbon dots for ultrasensitive and highly selective fluorescence detection and removal of Pb<Superscript>2+</Superscript>

A new type of self-targeting carbon dot (CD-Fla) for the detection of the toxic heavy metal ion Pb²⁺ was synthesized via a one-pot hydrothermal route using flavonoid extracts of Ginkgo biloba leaves as the starting material. As-prepared CD-Fla exhibited excellent biocompatibility and strong blue emission with a quantum yield of 16.1% and significant fluorescence quenching selectivity for Pb²⁺ without using any additional targeting molecules. CD-Fla could detect Pb²⁺ quantitatively within the range 0.1–20.0 nM, with an ultrahigh sensitivity of 55 pM. The selectivity of CD-Fla for Pb²⁺ was nearly one order of magnitude higher than that for other relevant metal ions. This was much better than ever reported CD-based metal ion sensors. The high sensitivity and selectivity were due to the incorporation of certain flavonoid-like moieties into CD-Fla. CD-Fla was also demonstrated to be a good probe for fluorescence tracing of intracellular Pb²⁺. The capability of CD-Fla was further improved when it was doped on agarose hydrogel. CD-Fla-doped agarose hydrogel (CD-AHG) allowed for visual fluorescence detection and removal of Pb²⁺ from water. This was confirmed by testing CD-AHG in actual water samples taken from the Jialing River (Chongqing, China). The Pb²⁺ adsorbed CD-AHG was regenerable in HCl solution. This study will open a new avenue for synthesizing intelligent materials capable of simultaneously targeting, detecting, and treating heavy metal ions.

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Diffusion coefficient of Fe<Superscript>2+</Superscript> in single-crystal ZnSe

The diffusion coefficient of Fe in single-crystal ZnSe has been measured in the temperature range 886–995°C. The 995°C diffusion coefficient is (47 ± 5) × 10⁻¹¹ cm²/s, and the average activation energy for Fe diffusion is 2.9 ± 0.3 eV.     

Influence of isovalent and heterovalent substitution for Bi<Superscript>3+</Superscript> and Fe<Superscript>3+</Superscript> on the properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript>-based solid solutions

Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi_2–хLa_хFe₄O₉ system, the limiting degree of La³⁺ substitution for Bi³⁺ ions in Bi₂Fe₄O₉ does not exceed 0.05 and that the limiting degree of substitution in the Bi₂Fe_4–2xTi_xCo_xO₉ system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La³⁺ for Bi³⁺ ions in Bi₂Fe₄O₉ and heterovalent substitution of Ti⁴⁺ and Co²⁺ ions for two Fe³⁺ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.     

Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Luminescence of GaS:Er<Superscript>3+</Superscript> and GaS:Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> layered crystals

Data are presented on the 300-K photoluminescence in GaS crystals doped with Er³⁺ or codoped with Er³⁺ and Yb³⁺. IR excitation (λ_ex = 976 nm) gives rise to anti-Stokes luminescence in GaS:Er³⁺ (0.1 at %) and GaS:Er³⁺,Yb³⁺ (0.1 + 0.1 at %) and leads to an increased intensity of the emission due to the ⁴ I _11/2 → ⁴ I _15/2 transitions. The anti-Stokes luminescence is shown to result from consecutive absorption of two photons by one Er³⁺ ion, and the increased intensity of Er³⁺ luminescence in GaS: Er³⁺,Yb³⁺ is due to energy transfer from Yb³⁺ to Er³⁺.     

Synthesis of Er<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> : Yb<Subscript>3+</Subscript> doped sol-gel derived silica glass and studies on their optical properties

Er₃₊ and Er₃₊ : Yb₃₊ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er₃₊ doped samples clearly revealed the absorption due to Er₃₊ ions. On the other hand Yb₃₊ : Er₃₊ doped samples showed enhanced absorption due to² F _7/2 →² F _5/2 transition. The absorption and emission cross-section for² F _7/2 ↔² F _5/2 of Yb³⁺ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm⁻¹. The 960 cm^-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.     

Luminescence of BaSiO<Subscript>3</Subscript> crystals doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript>

The Stokes and anti-Stokes luminescence of undoped and rare-earth-doped (Er³⁺ and Yb³⁺) BaSiO₃ has been studied in the temperature range 78–450 K under excitation at 10–1000 mV. The results indicate that the emission mechanism in BaSiO₃ crystals is hole recombination and that the anti-Stokes luminescence is due to consecutive sensitization; that is, the Yb³⁺ ions in the BaSiO₃ compound act as luminescence sensitizers, and the Er³⁺ ions, as activators.     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

Intense frequency upconversion luminescence in Yb<Superscript>3+</Superscript>/Tm<Superscript>3+</Superscript>-codoped oxychloride germanate glasses

Yb³⁺/Tm³⁺-codoped oxychloride germanate glasses for developing potential upconversion lasers have been fabricated and characterized. Structural properties were obtained based on the Raman spectra analysis, indicating that PbCl₂ plays an important role in the formation of glass network and has an important influence on the maximum phonon energies of host glasses. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions ¹G₄ → ³H₆ and ¹G₄ → ³H₄, respectively, were observed at room temperature. With increasing PbCl₂ content, the intensity of blue (477 nm) emission increases significantly, while the red (650 nm) emission increases slowly. The results indicate that PbCl₂ has more influence on the blue emissions than the red emission in oxychloride germanate glasses. The possible upconversion mechanisms are discussed and estimated. Intense blue upconversion luminescence indicates that these oxychloride germanate glasses can be used as potential host material for upconversion lasers.     

Synthesis of PANI/TiO<Subscript>2</Subscript>–Fe<Superscript>3+</Superscript> nanocomposite and its photocatalytic property

A convenient method for synthesizing highly photocatalytic activity PANI/TiO₂–Fe³⁺ nanocomposite was developed. The effect of calcination temperature on the phase composition of TiO₂ nanopowder was investigated. It was found that higher temperature could promote the formation of rutile phase. The nanocomposite was characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), infrared spectroscopy (IR) and X-ray diffraction (XRD). The results indicated that the nanohybrid was composed of TiO₂, Fe³⁺ and PANI. The photocatalytic property of the nanocomposite was evaluated by the degradation of methyl orange. In the presence of this catalyst, the degradation rate of methyl orange of 95.2% and 70.3% could be obtained under the UV and sunlight irradiation within 30 min, respectively. The apparent rate constant was 5.64 × 10⁻² which is better than that of the Degussa P25.     

Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> luminescence in calcium and strontium aluminates

Compound CaAl₄O₇ (CA4), SrAl₄O₇ (SA4), CaAl₁₂O₁₉ (CA12) and SrAl₁₂O₁₉ (SA12) have been synthesized by using single step combustion method. The phosphors have been characterized by XRD, SEM and PL techniques. Both CA4 and SA4 possess monoclinic crystal structure whereas CA12 and SA12 possess hexagonal structure. Effects of crystal symmetry on the emission spectrum have been studied by doping the samples with Ce³⁺ and Eu²⁺ ions. The luminescence properties of Ce³⁺ and Eu²⁺ in these hosts is discussed on the basis of their covalent character and the crystal field splitting of the d-orbital of dopant ions. The spectroscopic properties, crystal field splitting, centroid shift, red shift and stokes shift have been studied. Spectroscopic properties of Eu²⁺ ions have been accurately predicted from those of Ce³⁺ ions in the same host. Most importantly experimental results were matched excellently with the calculated results. The preferential substitution of Ce³⁺ and Eu²⁺ at different Ca²⁺, Sr²⁺ crystallographic sites have been discussed. The dependence of emission wavelengths of Ce³⁺ and Eu²⁺ on the local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Differences in the emission spectrum of these samples have been observed despite their similar crystal structures and space group. Possible reasons have been discussed.     

X-ray diffraction,optical absorption and emission studies on Er<Superscript>3+</Superscript>- and Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped Li<Subscript>3</Subscript>NbO<Subscript>4</Subscript> powder

Er³⁺(/Yb³⁺)-doped Li₃NbO₄ powder were prepared by thermally sintering mixtures of Er₂O₃ (0.5, 1.0 mol%), Yb₂O₃ (0, 0.5, 1.0 mol%), Li₂CO₃ (48–49 mol%) and Nb₂O₅ (50 mol%) at 1125, 1150 and 1450 °C over the durations of 8–22 h. The crystalline phases contained in these samples were determined by using X-ray diffraction and discussed in comparison with a vapor-transport-equilibration-treated (VTE-treated) Er(2.0 mol%):LiNbO₃ single crystal and ErNbO₄ powder previously reported. The results show that the X-ray patterns of the rare-earth-doped samples reveal little difference each other, but large differences with those of the VTE crystal and ErNbO₄ powder. The doped rare-earth ions Er³⁺ (and Yb³⁺) present in the powder as the ErNbO₄ (and YbNbO₄) phase(s). The possibility that the highly Er-doped LiNbO₃ crystal contains Li₃NbO₄ precipitates is small. Optical absorption and emission studies show that the only Er-doped Li₃NbO₄ powder shows similar absorption and emission characteristics with the pure ErNbO₄. The codopant Yb³⁺ ion enhances the 980-nm-upconversion emissions of Er³⁺ ions, results in remarkable spectral alterations at 0.98 μm region, and causes the alterations of relative absorbance and relative emission intensity of individual peaks or bands at 1.5 μm region. On the other hand, the Yb-codoping hardly affects the Er³⁺ energy structure and the lifetime of Er³⁺ ion at 1.5 μm. The measured lifetimes at 1.5 μm of Er³⁺ ions in the singly Er³⁺- and doubly Er³⁺/Yb³⁺-doped mixtures have a nearly same value of ∼ 1.5 ms. For the pure ErNbO₄ powder, the lifetime is prolonged to ∼2 ms perhaps due to radiation trapping effect.