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.     

Formation-decomposition equilibrium of the NpO<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>·UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> complex in chloride melts

The absorption spectra of the NpO ₂ ⁺ (5f ²) ion were examined in the region of the 3H ₅ ← ³ H ₄ magnetic dipole transition (1530–1760 nm) for series of melts with the UO ₂ ²⁺ concentration varied in the opposite directions: (1) NaCl-2CsCl eutectic melt with growing additions of the Cs₂UO₂Cl₄ complex salt and (2) Cs₂UO₂Cl₄ melt with growing additions of the NaCl-2CsCl mixture. Measurements of the integrated intensities of the bands belonging to the NpO ₂ ⁺ ·UO ₂ ²⁺ complex and unbound NpO ₂ ⁺ throughout the UO ₂ ²⁺ concentration range examined (up to 4.4 M in neat Cs₂UO₂Cl₄ melt) and processing of the data obtained in terms of the mass action law showed that the formation-decomposition reaction of the cation-cation complex can be described adequately only using the equation of reaction in the form NpO₂Cl ₄ ^3? + UO₂Cl ₄ ^2? ? {Cl₄ONpO?UO₂Cl₃}^4? = Cl^? (with the equilibrium constant of 1.3±0.1). Thus, the formation of the cationcation complex should be treated as replacement of chloride ion in the equatorial plane of uranyl(VI) by neptunyl(V), rather than as simple addition of UO ₂ ²⁺ to NpO ₂ ⁺ . The reverse reaction, decomposition of the cation-cation complex, consists essentially in replacement of neptunyl(V) by chloride ion.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on the dynamics of Li<Superscript>+</Superscript> ions in Li<Subscript>2</Subscript>O·P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Lithium ion transport has been studied in bismuth lithium phosphate glasses in the frequency range 20 Hz–1 MHz and in the temperature range 423–573 K using impedance spectroscopy. The addition of Bi₂O₃ in Li₂O·P₂O₅ glass is related to the modification of the glass structure and facilitates the Li⁺ ions migration. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. Conductivity of the present glass system is found to be ionic in nature. The electrical response of the glasses has been studied using both conductivity and electric modulus formalisms. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Nearly identical values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions overcome same energy barrier while conducting and relaxing.     

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.     

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.     

Magnetic and Electrical Properties of Al<Superscript>3+</Superscript> Implanted Co–ZnO

Co-doped ZnO ceramic samples sintered at four different temperatures were prepared by solid-state reaction method and implanted by Al ions subsequently. The microstructural, defect, magnetic and electrical properties of the samples were systematically investigated by x-ray diffraction, micro-Raman spectroscope, vibrating sample magnetometer and Hall measurement, respectively. The results show that all the samples exhibit room-temperature ferromagnetism with a saturation magnetization of 0.02–0.03 emu g^?1, the value of which is affected by the sintering temperature. The origin of room-temperature ferromagnetism is considered as the formation of Co²⁺– V _O–Co²⁺ bound magnetic polarons. Even though the implantation of Al³⁺ slightly reduces the saturation magnetization because of the lattice damage, less V _O and larger lattice spacing, however, an appropriate amount of Al³⁺ implantation and a proper sintering temperature can remarkably improve the electrical properties with the mobility of 200 ～300 cm² Vs^?1 and the resistivity of 20 ～40 Ω cm. In general, samples sintered at 1200^°C present more excellent comprehensive performances.     

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.     

Estimating the effect of C<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and C<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> radicals and neutral clusters on the fullerene formation

The mass spectrum of the products of arc discharge in helium between graphite electrodes has been studied for various values of the gas flow rate. As the gas flow rate increases, the intensity of C₆₀^±, C₇₀^±, C₈₄^± and C₉₀^± fullerene peaks increases and that of the C₂⁻ and C₃⁺ cluster radicals decreases, but the total decay in radicals amounts to only 21% of the total growth of fullerenes. From this it follows that a contribution to the formation of fullerenes from the neutral clusters (which are taken into account for the first time) significantly exceeds the contribution due to small radical species.     

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.     

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.     

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.     

Synthesis,electronic state,and particle size stabilization of nanoparticulate [Co(OH)<Subscript>2</Subscript>(H<Subscript>3</Subscript>O)<Stack><Subscript>δ</Subscript><Superscript>+</Superscript></Stack>]<Superscript>δ+</Superscript>

We have synthesized nanoparticulate cobalt(II) hydroxide containing Co²⁺ in tetrahedral oxygen coordination (Co _Td ²⁺ ), atypical of such systems: nano- [Co(OH)₂(H₃O) _δ ⁺ ]^δ+. The (Co _Td ²⁺ ) coordination in the hydroxide is inferred from its electronic diffuse reflectance spectrum, which shows a multiplet of strong absorption bands at 14500, 15000, and 16000 cm^?1 (⁴ A ₂(F)-⁴ T ₁(P) transition). Nanoparticulate cobalt(II) hydroxide forms in a weakly acidic medium under essentially nonequilibrium conditions due to supersaturation (by three to four orders of magnitude) with the starting reagents (CoCl₂ and LiOH) at the instant of the formation of the poorly soluble phase Co(OH)₂. Presumably, colloidal particles of nanoparticulate cobalt(II) hydroxide in a weakly acidic aqueous medium have a positive surface charge, compensated by a counter-ion (Cl^?) layer: nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ · δCl^?. The XRD patterns of pastes (gels) containing this hydroxide show three broad-ened lines with d = 5.31 (2θ = 16.7°), 2.77 (2θ = 32.3°), and 2.32 Å (2θ = 38.8°). According to small-angle X-ray scattering data, nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ has a narrow particle size distribution (1.0–2.0 nm). Synthesis and storage conditions are identified which ensure stabilization of the electronic state and particle size of nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ for a long time.     

Excitation of the uranyl ion in oxidation of U(IV) with xenon difluoride in frozen aqueous solutions of sulfuric acid: IV. Effect of F<Superscript>−</Superscript> and UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> ions

A specific feature of U(IV) oxidation with xenon difluoride in aqueous H₂SO₄ solutions is low-temperature chemiluminescence (CL), which in the course of warming the sample quickly cooled to 77 K is recorded starting from 165 K and reaches a maximum at about 200 K. Exothermic phase transitions, crystallization of the ice + H₂SO₄·4H₂O and ice + H₂SO₄·6.5H₂O eutectics, occur in the same temperature range. The data (temperature dependences of the chemiluminescence intensity and simultaneously recorded DTA curves) obtained in experiments with variation of the rate of mixing and cooling the solutions and of the concentrations of H₂SO₄ and F^? and UO ₂ ²⁺ ions are well explicable by the catalytic activity of the juvenile surface of H₂SO₄ crystal hydrates toward low-temperature reaction of U(IV) with XeF₂.     

Mechanochemical synthesis of γ-LiAlO<Subscript>2</Subscript> studied by <Superscript>6</Superscript>Li and <Superscript>27</Superscript>Al NMR and synchrotron X-Ray diffraction

The structural transformations accompanying the mechanochemical synthesis of fine-particle γ-LiAlO₂ have been studied by ⁶Li and ²⁷Al NMR and in situ X-ray diffraction. Mechanical activation of a mixture of aluminum hydroxide and lithium carbonate in an AGO-2 planetary mill results not only in size reduction, intermixing, and partial amorphization of the starting materials but also in the mechanochemical synthesis of a carbonate form of aluminum lithium hydroxide. Subsequent heat treatment of the mechanically activated mixture leads to the release of water and carbon dioxide molecules and the formation of an X-ray amorphous phase containing aluminum in octahedral and tetrahedral oxygen coordination. The X-ray amorphous material converts to gamma lithium aluminate through an intermediate phase.     

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.     

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.     

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.     

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.