Dynamic properties of P4O6S and P4O7:31P spin-echo and 31P MAS-NMR investigations.

The rotational dynamics of P₄O₆S and P₄O₇ in the solid state were studied by means of ³¹P NMR spectra of spinning and static powder samples in the temperature range of 153–295 K and 295–388 K, respectively. All spectra were simulated to confirm the type of the motion and to extract the time scales as a function of the temperature. Good agreement between experimental and theoretical data was obtained on the basis of a three-site jump model. For P₄O₆S, the activation energy and the pre-exponential factor derived from the lineshape simulations amount to 51(2) kJ/mol and 6(3)·10¹⁵ s⁻¹. For P₄O₇, the spectral analysis yields an activation energy of 67(1) kJ/mol and a pre-exponential factor of 6(2)·10¹⁴ s⁻¹. The dynamic behavior was checked independently by lineshape analyses under both MAS and static conditions. Activation energies are consistent within the errors for the lineshape analyses. Additionally, we have analyzed spin–lattice relaxation measurements, which show the correct trends for the activation energies.     

H NMR study of N(CH3)4H(ClF2CCOO)2

The proton spin–lattice relaxation times and ¹H NMR second moments were measured over a wide range of temperature. The results were compared with those of the ¹⁹F NMR relaxation that we obtained earlier. For both nuclear species, the evolution of the longitudinal magnetizations with time is observed to be strongly bi-exponential and were in good quantitative agreement with the cross-relaxation theory.     

Correlation between P chemical shift tensor and local structure in lithium cyclohexaphosphates Li6P6O18·3H2O and Li6P6O18

To understand the surprising behavior between the variations of the P′–P–P″ angles and the correlated variations of the O′–P–O″ ones, two lithium cyclohexaphosphate compounds Li₆P₆O₁₈·3H₂O and Li₆P₆O₁₈ are studied by solid state nuclear magnetic resonance (NMR) spectroscopy. The two compounds exhibit the same [P₆O₁₈]⁶⁻ ring anions but with 3m or internal symmetry, respectively. Such symmetries induce local distortions that are exhibited by NMR spectroscopy. One-dimensional (1D) NMR gives information on structural sites of ⁷Li and ³¹P ions and the crystallographic non-equivalencies are observed. Nevertheless, in the anhydrous compound, X-ray diffraction and NMR results do not completely agree and some discrepancy exists between the number of sites observed with the first technique and the number of lines exhibited in the NMR spectra either for ⁷Li or ³¹P nuclei. This problem is elucidated by using 2D double quantum NMR spectroscopy coupled with theoretical considerations. We find that the ³¹P chemical shift tensor is dependent on the deviations of the O–P–O angles from those in the regular tetrahedron. Within the same empirical model, we suggest that the surprising behavior between the variations of the P′–P–P″ and the ones of the O′–P–O″ is related to the overall charge on the PO₄ group. We also find the positions of the isotropic lines for ⁷Li essentially depend on the site co-ordination of this nuclei.     

Synthesis and luminescent properties of nanoparticles LaSrAl3O7:Eu, Tb

Phosphors of nanoparticles LaSrAl₃O₇:RE³⁺(REEu, Tb) have been prepared by a sol–gel method. The structure and luminescent properties of LaSrAl₃O₇:Eu³⁺ and LaSrAl₃O₇:Tb³⁺ phosphors were characterized by X-ray diffraction and atomic force microscopy (AFM), photoluminescence excitation and emission spectra were utilized. From X-ray diffraction (XRD) patterns, it is indicated that the phosphor LaSrAl₃O₇ forms without impurity phase at 900 °C. From atomic force microscopy (AFM) images, it is shown that the crystal size of the phosphores are about 60–80 nm. Upon excitation with UV irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀–⁷F₂ transition of Eu³⁺, and at around 545 nm corresponding to the ⁵D₄–⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺(or Tb³⁺) concentration and annealing temperature were also studied in detail.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between luminescent centre and Eu³⁺ ions.     

Synthesis and magnetic properties of Sm–Y3Fe5O12 nanoparticles

Garnet nanoparticles Y_3−xSm_xFe₅O₁₂ were fabricated by a sol–gel method. The XRD patterns of all the samples have only peaks of the garnet structure and the sizes range from 34 to 67 nm. Results of VSM show that the saturation magnetization of Y_3−xSm_xFe₅O₁₂ (0<x3) decreases on increasing the Sm concentration x evidently. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the nanoparticle size is increased.     

Synthesis and properties of colloidal ternary ZnGa2O4:Eu nanocrystals

A nonhydrolytic hot solution synthesis technique was used to grow monodisperse ternary oxide nanocrystals of ZnGa₂O₄:Eu³⁺. The shape of ZnGa₂O₄:Eu³⁺ nanocrystals was a function of the type of precursor, and their size was controlled by changing the concentration ratio of Zn precursor to surfactant. The crystal structure of synthesized ZnGa₂O₄ nanocrystals was a cubic spinel with no detectable secondary phases. Photoluminescence of red-emitting ZnGa₂O₄:Eu³⁺ nanocrystals resulted in a high (⁵D₀-⁷F₂)/(⁵D₀-⁷F₁) intensity ratio, suggesting that the Eu³⁺ ions occupy tetrahedral Zn²⁺ sites or distorted octahedral Ga³⁺ sites with no inversion symmetry in ZnGa₂O₄ nanocrystals.     

Polarizing Microscopic and 31P NMR Studies of Decylammonium Chloride/Potassium Chloride/Water System. Containing Phosphoric Acid Monodecyl Ester and H3PO4

The decylammonium chloride (DACl), KCl and D₂O system forms two phases(N_c+N_d) in the nematic range. The N_d phase was ca. 15% by volume and exhibited extinct appearance. From conoscopic measurements it was inferred that the optical axis of the N_d phase was tilted. The lamellar phase of the DACl-KCl-D₂O system as well as the lamellar phase obtained by adding phosphoric acid decylester/phosphoric acid (PDE/H₃PO₄) showed the following phase sequence: L_α + N_d 35°C H_α + N_d 40°C N_c + N_d 45°C N_c 50°C isotropic The line shapes of ³¹P NMR of PDE/H₃PO₄ were found to be sensitive to micelle size and dynamics occuring in the lyotropic system, but they do not differentiate between different micelle shapes.     

Synthesis and luminescent properties of Y6W2O15:Eu phosphors

In this paper, a novel phosphor, Y₆W₂O₁₅:Eu³⁺ was synthesized by thermal decomposition and phase transition of its decatungstate gel precursor. With stepwise increase of temperature to 750 °C, a crystalline phase of Y₆W₂O₁₅:Eu³⁺forms that gives intense red emission when excited at 466 nm, the emission is attributed to the Eu³⁺ ions transitions from ⁵D₀ excited states to ⁷F_J (J=0-4) ground states. The long excitation wavelength proves the Eu³⁺ transition follows the photoexcitation of the oxygen-metal (O→W lmct) charge transfer bands in yttrium tungstate. Some structural information regarding Y₆W₂O₁₅ provided by luminescence is in accord with that characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The long-wavelength excitation properties of this material may find application in the production of red phosphors for white light-emitting diodes (LEDs).     

Photoluminescence properties and effects of dopant concentration in Bi2ZnB2O7:Tb phosphor

A novel green phosphor, Tb³⁺ doped Bi₂ZnB₂O₇ was synthesized by conventional solid state reaction method. The phase of synthesized materials was determined using the XRD, DTA/TG and FTIR. The photoluminescence characteristics were investigated using spectrofluorometer at room temperature. Bi₂ZnB₂O₇:Tb³⁺ phosphors excited by 270 nm and 485 nm wavelengths. The emission spectra were composed of three bands, in which the dominated emission of green luminescence Bi₂ZnB₂O₇:Tb³⁺ attributed to the transition ⁵D₄ → ⁷F₅ is centered at 546 nm. The dependence of the emission intensity on the Tb³⁺ concentration for the Bi_2−xTb_xZnB₂O₇ (0.01 ≤ x ≤ 0.15) was studied and observed that the optimum concentration of Tb³⁺ in phosphor was 13 mol% for the highest emission intensity at 546 nm.     

Thermoluminescent and stuctural properties of BaAl2O4:Eu,Nd,Gdphosphors prepared by combustion method

BaAl₂O₄:Eu²⁺,Nd³⁺,Gd³⁺ phosphors were prepared by a combustion method at different initiating temperatures (400–1200 °C), using urea as a comburent. The powders were annealed at different temperatures in the range of 400–1100 °C for 3 h. X-ray diffraction data show that the crystallinity of the BaAl₂O₄ structure greatly improved with increasing annealing temperature. Blue-green photoluminescence, with persistent/long afterglow, was observed at 498 nm. This emission was attributed to the 4f⁶5d¹–4f⁷ transitions of Eu²⁺ ions. The phosphorescence decay curves were obtained by irradiating the samples with a 365 nm UV light. The glow curves of the as-prepared and the annealed samples were investigated in this study. The thermoluminescent (TL) glow peaks of the samples prepared at 600 °C and 1200 °C were both stable at ∼72 °C suggesting that the traps responsible for the bands were fixed at this position irrespective of annealing temperature. These bands are at a similar position, which suggests that the traps responsible for these bands are similar. The rate of decay of the sample annealed at 600 °C was faster than that of the sample prepared at 1200 °C.     

Surface characterization and luminescent properties of SrAl2O4:Eu,Dy nano thin films

SrAl₂O₄:Eu²⁺, Dy³⁺ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O₂ atmospheres was most probably responsible for the quenching of the PL intensity after annealing.     

Synthesis of Gd2Ti2O7:Eu, V phosphors by sol-gel process and its luminescent properties

A red-emitting phosphor material, Gd₂Ti₂O₇:Eu³⁺, V⁴⁺, by added vanadium ions is synthesized using the sol-gel method. Phosphor characterization by high-resolution transmission electron microscopy shows that the phosphor possesses a good crystalline structure, while scanning electron microscopy reveals a uniform phosphor particle size in the range of 230-270 nm. X-ray photon electron spectrum analysis demonstrates that the V⁴⁺ ion promotes an electron dipole transition of Gd₂Ti₂O₇:Eu³⁺ phosphors, causing a new red-emitting phenomenon, and CIE value shifts to x=0.63, y=0.34 (a purer red region) from x=0.57, y=0.33 (CIE of Gd₂Ti₂O₇:Eu³⁺). The optimal composition of the novel red-emitting phosphor is about 26% of V⁴⁺ ions while the material is calcinated at 800  °C. The results of electroluminescent property of the material by field emission experiment by CNT-contained cathode agreed well with that of photoluminescent analysis.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Preparation and optical properties of ZnGa2O4:Cr thin films derived by sol-gel process

ZnGa₂O₄:Cr³⁺ thin films with bright red emission were synthesized using a sol-gel process, characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Auger electron spectroscopy (AES) and UV-vis and fluorescence spectrophotometry measurements. Effects of calcining temperature, film thickness, calcining duration and substrates on the crystal structure and photoluminescent property have been investigated. It is found that the crystallinity, Ga/Zn ratio and band gap energy (E_g) are significant factors influencing optical characteristics, while the nature of substrates affect the surface morphologies of ZnGa₂O₄:Cr³⁺ thin films.     

Phosphorescent and thermoluminescent properties of SrAl2O4:Eu,Dy phosphors prepared by solid state reaction method

Long persistent SrAl₂O₄:Eu²⁺ phosphors co-doped with Dy³⁺ were prepared by the solid state reaction method. The main diffraction peaks of the monoclinic structure of SrAl₂O₄ were observed in all the samples. The broad band emission spectra at 497 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ were observed and the emission is attributed to the 4f⁶5d¹ to 4f⁷ transition of Eu²⁺ ions. The samples annealed at 1100–1200 °C showed similar broad TL glow curves centered at 120 °C. The similar TL glow curves suggest that the traps responsible for them are similar. The long afterglow displayed by the phosphors annealed at different temperatures, may be attributed to the Dy³⁺ ions acting as the hole trap levels, which play an important role in prolonging the duration of luminescence.     

Optical properties of γ-Fe2O3 nanoparticles dispersed on sol–gel silica spheres

Two types of γ-Fe₂O₃ nanoparticles, pure γ-Fe₂O₃ and γ-Fe₂O₃ dispersed on sol–gel silica spheres (γ-Fe₂O₃/SiO₂) in thin film form were prepared by the sol–gel technique. Transmission electron microscopy, X-ray diffraction, optical transmittance and FTIR studies along with photoluminescence measurements were carried out for characterizing the samples. The X-ray diffraction patterns of both γ-Fe₂O₃ nanoparticles and γ-Fe₂O₃/SiO₂ indicated their phase-pure forms which were supported by the FTIR spectra. The average sizes of the nanoparticles obtained from transmission electron microscopy studies were 4 nm for both types of samples. Optical transmittance studies indicated direct allowed transitions with two band gaps at 2.43 and 3.07 eV. Although both types of samples showed excitonic luminescence at 2.38 eV (at room temperature), the luminescence intensity of the γ-Fe₂O₃/SiO₂ was higher than that of pure γ-Fe₂O₃.     

Synthesis and luminescent properties of nanoparticles GdCaAl3O7:RE (RE=Eu, Tb) via the sol-gel method

By using metal nitrates as starting materials and citric acid as complexing agent, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ powder phosphors were prepared by a citrate-gel method. Thermal analysis (TG-DTG), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results of the XRD indicated the precursor samples began to crystallize at 800 °C and the crystallinity increased with elevation the annealing temperature. TEM images showed that the phosphor particles were basically of spherical shape, with good dispersion about a particle size of around 40-70 nm. Upon excitation with UV irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole ⁵D₀-⁷F₂ transition of Eu³⁺, and at around 543 nm corresponding to the ⁵D₄-⁷F₅ transition of Tb³⁺. The dependence of photoluminescence intensity on Eu³⁺ (or Tb³⁺) concentration and annealing temperature were also studied in detail.     

The 2D {P} Spin-Echo-Difference Constant-Time [C, H]-HMQC Experiment for Simultaneous Determination of JH3′P and JC4′P in C-Labeled Nucleic Acids and Their Protein Complexes

A two-dimensional {³¹P} spin-echo-difference constant-time [¹³C, ¹H]-HMQC experiment (2D {³¹P}-sedct-[¹³C, ¹H]-HMQC) is introduced for measurements of ³J_C4′P and ³J_H3′P scalar couplings in large ¹³C-labeled nucleic acids and in DNA–protein complexes. This experiment makes use of the fact that ¹H–¹³C multiple-quantum coherences in macromolecules relax more slowly than the corresponding ¹³C single-quantum coherences. ³J_C4′P and ³J_H3′P are related via Karplus-type functions with the phosphodiester torsion angles β and ε, respectively, and their experimental assessment therefore contributes to further improved quality of NMR solution structures. Data are presented for a uniformly ¹³C, ¹⁵N-labeled 14-base-pair DNA duplex, both free in solution and in a 17-kDa protein–DNA complex.