Spectroscopic properties of Nd<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript>-doped and Nd<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript>-codoped high silica glass

The Nd³⁺, Yb³⁺-doped and Nd³⁺–Yb³⁺-codoped high silica glasses (HSGs) were fabricated by sintering porous glasses impregnated with Nd³⁺ and Yb³⁺ ions solutions. The Judd–Ofelt theory was used to study the spectroscopic properties of Nd³⁺-doped HSGs. Large parameter Ω₂ of Nd³⁺-doped HSGs suggests a lower centrosymmetric coordination environment around the Nd³⁺ in HSG. The spontaneous emission probability and emission cross-section (σ_em) of Yb³⁺-doped HSGs are obtained. A broad emission band from 950 to 1,100 nm was detected when the Nd³⁺–Yb³⁺-codoped HSG was excited by 808 nm LD. The energy transfer process from Nd³⁺ to Yb³⁺ in HSG was described in this paper.     

High-temperature tensile-hold crack-growth behavior of HASTELLOY<Superscript>®</Superscript> X alloy compared to HAYNES<Superscript>®</Superscript> 188 and HAYNES<Superscript>®</Superscript> 230<Superscript>®</Superscript> alloys

The creep–fatigue crack-growth tests of HASTELLOY^® X alloy were carried out at the temperatures of 649°C, 816°C, and 927°C in laboratory air. The experiments were conducted under a constant stress-intensity-factor-range (ΔK) control mode with a R-ratio of 0.05. In the constant ΔK tests, a ΔK of 27.5 MPa\(\sqrt{\mathrm{m}}\) and a triangular waveform with a frequency of 0.333 Hz were used. Various tensile hold times at the maximum load were imposed to study fatigue and creep–fatigue interactions. Crack lengths were measured by a direct current potential drop method. In this paper, effects of hold time and temperature on the crack-growth rates are discussed. Furthermore, the crack-growth rates of the HASTELLOY^® X alloy are compared to those of the HAYNES^® 188 and HAYNES^® 230^® superalloys.     

Crystal structure of compounds CsA<Superscript>V</Superscript>A′<Superscript>VI</Superscript>O<Subscript>6</Subscript> (A<Superscript>V</Superscript> = Sb,Ta; A′<Superscript>VI</Superscript> = W,U)

Compounds CsA^VA′^VIO₆ (A^V = Sb, Ta; A′^VI = W, U) were synthesized by high-temperature solidphase reactions. The crystal structures of the compounds were refined by the Rietveld method (space group Fd \(\bar 3\) m).     

Comparison of an experimental bone cement with surgical Simplex<Superscript>®</Superscript> P,Spineplex<Superscript>®</Superscript> and Cortoss<Superscript>®</Superscript>

Conventional polymethylmethacrylate (PMMA) cements and more recently Bisphenol-a-glycidyl dimethacrylate (BIS-GMA) composite cements are employed in procedures such as vertebroplasty. Unfortunately, such materials have inherent drawbacks including, a high curing exotherm, the incorporation of toxic components in their formulations, and critically, exhibit a modulus mismatch between cement and bone. The literature suggests that aluminium free, zinc based glass polyalkenoate cements (Zn-GPC) may be suitable alternative materials for consideration in such applications as vertebroplasty. This paper, examines one formulation of Zn-GPC and compares its strengths, modulus, and biocompatibility with three commercially available bone cements, Spineplex, Simplex P and Cortoss. The setting times indicate that the current formulation of Zn-GPC sets in a time unsuitable for clinical deployment. However during setting, the peak exotherm was recorded to be 33 degrees C, the lowest of all cements examined, and well below the threshold level for tissue necrosis to occur. The data obtained from mechanical testing shows the Zn-GPC has strengths of 63 MPa in compression and 30 MPa in biaxial flexure. Importantly these strengths remain stable with maturation; similar long term stability was exhibited by both Spineplex and Simplex P. Conversely, the strengths of Cortoss were observed to rapidly diminish with time, a cause for clinical concern. In addition to strengths, the modulus of each material was determined. Only the Zn-GPC exhibited a modulus similar to vertebral trabecular bone, with all commercial materials exhibiting excessively high moduli. Such data indicates that the use of Zn-GPC may reduce adjacent fractures. The final investigation used the well established simulated body fluid (SBF) method to examine the ability of each material to bond with bone. The results indicate that the Zn-GPC is capable of producing a bone like apatite layer at its surface within 24 h which increased in coverage and density up to 7 days. Conversely, Spineplex, and Simplex P exhibit no apatite layer formation, while Cortoss exhibits only minimal formation of an apatite layer after 7 days incubation in SBF. This paper shows that Zn-GPC, with optimised setting times, are suitable candidate materials for further development as bone cements.     

<Superscript>172</Superscript>Hf → <Superscript>172</Superscript>Lu Radionuclide Generator Based on a Reverse-Tandem Separation Scheme

The distribution coefficients of Hf(IV) and Lu(III) between Dowex 50W×8 cation exchanger or Dowex 1×8 anion exchanger and mixed HCl–H₂C₂O₄ solutions and between Dowex 50W×8 cation exchanger or Dowex 1×8 anion exchanger and citric acid solutions were determined. A number of modifications of the ¹⁷²Hf → ¹⁷²Lu generator, based on reverse separation schemes, were examined. Systems consisting of an anion-exchange resin and a solution of appropriate organic acid were taken as a chemical basis of the generator. Irreversible sorption of ¹⁷²Lu in generator columns was studied. The optimum operation mode of the ¹⁷²Hf → ¹⁷²Lu generator based on the reverse-tandem scheme with periodic transfer of the parent radionuclide into the liquid phase was determined.     

Use of a nanostructured material for separation of <Superscript>238</Superscript>U and <Superscript>237</Superscript>U produced by the photonuclear reaction <Superscript>238</Superscript>U(γ, <Emphasis Type="Italic">n</Emphasis>)<Superscript>237</Superscript>U

²³⁷U was produced by the reaction ²³⁸U(γ, n) on an electron accelerator, MT-25 microtron, at the Flerov Laboratory of Nuclear Reactions. For the separation of ²³⁷U and [²³⁸U, the recoil nuclei were collected by a nanostructured material, hydrated manganese dioxide (of the cryptomelane type), in the solid-solid system. From fission products, ²³⁷U was separated by ion exchange. The specific activity of the resulting ²³⁷U was 4.5 × 10⁹ Bq (mg ²³⁸U)^-1, with the content of radioactive impurities of ≤10^-6 Bq Bq^-1. The chemical yield of ²³⁷U was 80%.     

The effect of temperature instability on the threshold sensitivity of photodetectors based on A<Superscript>III</Superscript>–B<Superscript>V</Superscript> photodiodes

The dependence of the sensitivity of photodetectors based on A^III–B^V photodiodes on accidental variations of the temperature of its elements is analyzed. It is shown that the temperature drift of the bias level in input circuits of op-amps strongly contributes to the resulting photodetector noise up to frequencies on the order of 1 MHz. To reach the limiting sensitivities of the sensors, it is necessary to stabilize the temperature of not only the photodiode chip, but also the integrated circuit of the first amplifier stage. For most of applications, the required stabilization accuracy does not exceed ±0.1°C. As a result of the analysis, prototype high-sensitivity medium-wavelength (2–5 μm) sensors were developed that operate without forced cooling and have a detection threshold of tens of nanowatts at a detection bandwidth of 0–1 MHz.     

Controllable white light emission from Dy<Superscript>3+</Superscript>–Eu<Superscript>3+</Superscript> co-doped KCaBO<Subscript>3</Subscript> phosphor

Potassium calcium borate, KCaBO₃:Eu³⁺ phosphors with various Dy³⁺ concentrations (0–3 wt%) were synthesized by solid state reaction and studied for the first time. Under various UV–violet excitations, the obtained single monoclinic phased Dy³⁺–Eu³⁺ co-doped KCaBO₃ polycrystalline phosphors emit a combination of yellow–blue and red–orange wavelength giving intense white light, which can easily be controlled by varying the concentration of Dy³⁺. The increase in white light emission with the increase of Dy³⁺ concentration indicates the efficient energy inter-ion transfer from Dy³⁺ to Eu³⁺ ions. Furthermore, the observed emission lifetimes and the intense white light emission are suggestive exploration for the present phosphor for potential optoelectronic applications such as white light-emitting phosphor for blue LEDs chips.     

Characterization of <Superscript>4</Superscript>I<Subscript>9/2</Subscript> ↔ <Superscript>4</Superscript>F<Subscript>3/2</Subscript> optical transitions in trivalent Nd<Superscript>3+</Superscript> ions in GaLaS glass

The positions of Stark levels have been determined, using a step-by-step procedure, in the ⁴I_9/2 and ⁴F_3/2 manifolds of Nd³⁺ ions from absorption and photoluminescence measurements in the 12–293 K temperature range. This data has been used to calculate the emission cross-section for which the maximum value turns out to be ～2.3 × 10^?20 cm². The radiative recombination time, calculated using Judd–Ofelt analysis, of the ⁴F_3/2 manifold is in close vicinity to the experimentally determined times that were measured by the conventional decay of PL after interruption of excitation and by QFRS. Moreover, the peak time defined by QFRS is independent of temperature. Therefore, the dominant relaxation mechanism from the ⁴F_3/2 excited manifold of Nd³⁺ ions in GaLaS glass is believed to be by radiative emission.     

Distribution of <Superscript>210</Superscript>Ро in lichen thalli

Distribution of ²¹⁰Po in thalli of soil and wood (epiphytic) lichens was studied. Four fractions containing the corresponding ²¹⁰Ро forms were obtained by sequential extraction: (1) intercellular, (2) extracellular, (3) intracellular, and (4) insoluble thallus residue. The ²¹⁰Ро uptake by lichens is mainly passive, as the total content of the radionuclide in fractions 1, 2, and 4 reaches 88–97%. From 3 to 12% of ²¹⁰Ро is taken up actively (fraction 3), and for soil lichens this parameter is approximately 2.75 times higher than for epiphytic lichens. Presumably, ²¹⁰Ро is supplied into soil and epiphytic lichens in the form of different chemical compounds and is therefore characterized by different bioavailability.     

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.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

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.     

Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Er<Superscript>3+</Superscript>,Ce<Superscript>3+</Superscript>—A new “invisible” IR phosphor

Ce³⁺ doping of Y₂O₂S:Er³⁺ can be used to suppress the visible anti-Stokes luminescence of the phosphor under excitation in the range 0.90–0.98 μm. We take advantage of this effect to create a new, efficient “invisible” IR phosphor emitting in the range 1.5–1.6 μm.     

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.     

Stability of the LaCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> and LuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> Ions Studied by Mass Spectrometry

The enthalpy stability of the LaCl ₄ ^? and LuCl ₄ ^? ions is assessed using high-temperature mass spectrometry. The enthalpy of Cl^? detachment is determined to be Δ_rH⁰(298.15 K) = 332 ± 10 kJ/mol for LaCl ₄ ^? and 359 ± 10 kJ/mol for LuCl ₄ ^? .     

Cyclic loading and fracture mechanics of Ductal<Superscript>®</Superscript> concrete

Reactive Powder Concrete (RPC) is a special type of ultra high strength, superplasticized, silica fume concrete, often fibre-reinforced, with improved homogeneity because the traditional coarse and fine aggregate are replaced by fine sand with particle sizes in the range of 100–400 μm [4–16 thousandths of an inch]. RPC properties are attractive because compressive strengths up to 800 MPa [116 ksi] have been recorded, but more typically in excess of 200 MPa [29 ksi]. Flexural strengths up to 141 MPa [20.4 ksi] and fracture energy of 40 kJ/m²[kJ/in.²] have been reported—the latter achieved when steel or stainless steel fibres were included in the mix (Baché (1998) Proceedings of the 2nd international conference on superplasticizers in concrete, Ottawa, pp 35–41; Coppola et al. L’Industria Ital Cemento 707:112–125 (1996); Blais and Couture PCI J 44(5):60–71 (1999); Richard and Cheyrezy (1994) Proceedings of V. Mohan Malhotra symposium on concrete technology: past, present, and future (SP 144). American Concrete Institute, Detroit, pp 507–518; Richard and Cheyrezy Cement Concrete Res 25(7):1501–1511 (1995)). Ductal^®, a commercial RPC, has a compressive strength of approximately 150 MPa [22 ksi] with metallic or organic fibres. All tests described here were performed on 40 × 40 × 160 mm [1.6 × 1.6 × 6.3 in.] (Width (b) × Depth (d) × length (L)) prisms with Poly Vinyl Alcohol (PVA) fibres. Ductal^® is a family of RPC and micro-defect-free concretes containing micro silica, silica fume, cement, Quartz sand, superplasticizer, and PVA fibres. Mechanical and fracture parameters were investigated using four point bending. Low and high cyclic fatigue tests were conducted in three stages, starting from low to high strain cycles. Cracks generated by cyclic fatigue tests were monitored periodically in order to evaluate the rate of crack propagation. Cracks were also investigated using a high magnification microscope. Three pairs of specimens were tested, notched and un-notched to evaluate fracture parameters. Four point bending was used again because determination of the J-Integral (J _IC ) requires the application of pure bending over a portion of the beam. Load was applied at the third points over a span (S) of 120 mm [4.7 in.], providing a span to depth ratio (S/d) of 3.0. Specimens were notched using a 1 mm [0.04 in.] thick diamond saw. The crack tip generated was circular and the crack length (s) was approximately 10 mm [0.4 in.]. Tests on the notched specimens included measurement of the crack mouth opening displacement (CMOD). Closed-loop testing was developed using a feed back signal from the (CMOD) clip gauge attached to the notched specimens and from strain gauges attached to the un-notched specimens. The weight (w) of each specimen was obtained prior to testing. Fracture parameters were calculated from the load–deflection curves obtained from the notched and un-notched specimens.     

Characterization of CBD–CdS nanocrystals doped with Co<Superscript>2+</Superscript>

Co-doped CdS nanofilms are synthesised by chemical bath deposition growth technique at the temperature of 60?±?2 °C. The cobalt molar fraction was ranged from 0 ≤ x ≤ 5.47, which was determined by energy-dispersive X-ray spectroscopy. The X-ray diffraction shows that the nanofilms are of CoS–CdS nanocomposites with individual CdS and CoS crystalline planes. The Co-doped CdS crystalline phase was zinc-blende that was determined by X-ray diffraction and confirmed by Raman spectroscopy. The average grain size of the CdS films was ranged from 2.56 to 1.67 nm that was determined by Debye–Scherrer equation from ZB (111) direction and it was confirmed by Wang equation and high resolution transmission electron microscopy (HRTEM). Raman scattering shows that the CdS lattice dynamics is characteristic of a bimodal behaviour, in which the first optical longitudinal mode denotes the characteristic peak at 305 cm^?1 of the CdS nanocrystals that is associated with the cobalt incorporation. Nanofilms present two main bandgaps at ~?2.56 and 3.80 eV, which are attributed to single CdS and quantum-confinement due to nanocrystals size. The increase in band gap with increase in cobalt concentration suggests intermetallic compound of CoS (E_g = 1.60 eV) with CdS (E_g = 2.44 eV). The CdS nanocrystals size was ranged from 2.46 to 1.81 nm that was determined from ZB (111) direction by Debye–Scherrer equation and confirmed by the Wang equation. The room-temperature photoluminescence of the Co-doped CdS presents well-resolved radiative bands associated to structural defects and with the quantum-confinement. For the Co-doped CdS the photoluminescence intensity increases indicate a high-passivation of the nanocrystals.     

Refinement of the energy characteristics of <Superscript>213</Superscript>Bi α-radiation

Results of experiments on determination of the energy of ²¹³Bi α-particles for the existing lines with the intensities of 1.94 and 0.15% per decay are reported. The results were obtained by semiconductor α-ray spectrometry by comparison with the α-particle energies for the major lines of ²²¹Fr and ²¹³Po, known with a lower uncertainty. The experiments were designed so as to minimize and, at the same time, take into account factors affecting the deviations of the peak maxima from the true values. Special emphasis is made on the decay of recoil nuclei on the detector surface. To eliminate this effect, samples containing highly nonequilibrium systems ²¹³Bi + ²²¹Fr and ²¹³Bi + ²²⁵Ac were prepared. For the measurement conditions used, the equilibrium spectra of ²²⁵Ac with daughter decay products were found to be unsuitable for accurate determination of the energy of the ²¹³Bi major peak and can be used only for tentative estimations. The actual energies of ²¹³Bi α-radiation do not coincide with the assessed reference data used today and are in the region of the upper limit of the uncertainty range for these data. The results show that the presently used energy characteristics of ²¹³Bi α-radiation require refinement.