Synthesis,structural and optical properties of Eu3+–doped Ca2V2O7 nanophosphors

Europium doped calcium pyrovanadate nanoparticles Ca₂V₂O₇:Eu³⁺, having a size of 57–63 nm, were synthesized using combustion process. Structure, morphological and optical properties of nanophosphors have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectrometry (PL) and Fourier transform infra-red (FT-IR) spectroscopy. X-ray studies shows that a pure triclinic Ca₂V₂O₇ phase was obtained at 900 °C temperature. The red emission observed at 620 nm upon excitation at 305 nm is due to hypersensitive transition ⁵D₀ → ⁷F₂ of luminescent activator Eu³⁺ location at a site with no inversion symmetry in Ca₂V₂O₇ crystal lattice. High luminescent intensity and easy synthesis technique make this red phosphor a promising candidate for application as luminescent materials.     

Synthesis and optical properties of Co3O4 porous nanoplates converted from α-Co(OH)2 nanoplates

A two-step strategy has been developed for the preparation of pure cubic phase Co₃O₄ porous nanoplates with visible light photoluminescence.

1. Download : Download high-res image (206KB)
2. Download : Download full-size image

     

Electronic and optical properties of Ti3+ doped α-Al2O3 crystals: First-principles calculations

Based on density functional theory, the geometric and electronic structures of the Ti doped α-Al₂O₃ system (Ti:α-Al₂O₃) are calculated by using a first-principles method. Due to the Ti-doping, both the lengths and angles of bonds in the local geometries are distorted, from which a trigonal–triclinic structural transition may be expected. With increasing Ti-doping, an insulator–semimetal transition is observed in the Ti:α-Al₂O₃ system, mainly due to a complete spin polarization of electrons at the Fermi level. The dielectric function and absorption edge are further calculated. It is found that the absorption edge is decreased, and is much lower than that of pure Al₂O₃ crystals, which is in good agreement with the experiment. The results indicate the potential applications of the Ti:α-Al₂O₃ optical system.     

Structural, spectroscopic and crystal field analyses of Ni2+ and?Co2+ doped Zn2SiO4 powders

In this paper we presented structural and spectroscopic study of zinc silicate powder samples doped with divalent nickel and cobalt ions. Results of the Rietveld structural refinement, combined with optical spectroscopic study and theoretical crystal field calculations, are presented and discussed. X-ray diffraction studies were performed to establish reliable structure of the doped samples; in this way the interionic distances and chemical bond angles in Zn₂SiO₄:Co²⁺ and Zn₂SiO₄:Ni²⁺ were calculated and are reported for the first time. The room temperature reflection spectra of the prepared samples were measured in a spectral region from 4000 to 50000 cm^?1. The exchange charge model of crystal field has been applied to analyze the experimental spectra and assign all observed details in the spectra to the corresponding electronic transitions between the Co²⁺ and Ni²⁺ crystal field energy levels. The only input information for the model calculation was the experimentally obtained structural data, which were used for the calculations of the crystal field parameters with subsequent diagonalization of the crystal field Hamiltonian for both ions. Agreement between the calculated and experimentally detected energy levels of impurity ions was good. On the basis of the crystallographic and crystal field studies it was established that there exists a systematic trend of preferential occupation of one out of two possible crystallographic sites (namely, Zn2) for both impurity ions.     

Theoretical investigation of electronic,magnetic, transport and optical properties of the pure and doped cuprate superconductor HgBa2CuO4+δ

We report detailed DFT calculations and Monte Carlo simulations on the pure and doped cuprate superconductor HgBa₂CuO_4+δ. For the pure compound (δ = 0), we have obtained an insulating behavior with strong antiferromagnetic copper spin correlations in the CuO₂ plane. The high value of the calculated Néel temperature T_N = 333 K reflects the large in-plane exchange interaction J = -145 meV. The obtained optical properties and critical exponents demonstrate the anisotropic quasi-2D character of this type of materials. As for the doped compound the electronic structure and the transport properties have been investigated for various values of doping. Based on these data, we suggest a prediction of the value of optimum doping for HgBa₂CuO_4+δ(δ_optimal = 0.125).     

Electrical and optical properties of pure and Pb2+ ion doped PVA???PEG polymer composite electrolyte films

Pb²⁺ ion conducting polymer composite electrolyte films, based on polyvinyl alcohol and polyethylene glycol doped with Pb(NO₃)₂ salt, were prepared using the solution cast technique. X-ray diffraction patterns of polymer composite with salt reveal the decrease in the degree of crystallinity with increasing concentration of the salt. The dielectric plots show an increase in dielectric permittivity at low frequency side with increasing salt concentration as well as temperature. The frequency dependence of ac conductivity obeys the Jonscher power law, and the maximum dc conductivity value is found to be 2.264×10^?7 S/m at 303?K for the polymer composite with 30?mol% Pb(NO₃)₂. The activation energy for the ion in polymer electrolyte has been calculated from the modulus plots, and is in good agreement with the activation energy calculated from the temperature-dependent dc conductivity plot. The modulus plots indicate the non-Debye nature of the sample. For pure and doped films at room temperature, the impedance plots exhibit only one semicircle, indicating the presence of one type of conduction mechanism, whereas for 30?mol% salt doped with electrolyte film at different temperatures, it demonstrated the existence of bulk and electrode?Celectrolyte interface properties. Optical absorption spectra show a broad peak for all complexes, while compared with pure polymer composite, due to the complex formation of polymer electrolyte with Pb(NO₃)₂ and their absorption edge, direct band gap and indirect band gap were calculated. It was found that the absorption edge and energy gap values decreased on doping with Pb(NO₃)₂ dopant.     

Effective conversion of copper-vapor laser emission in a β-BaB2O4 crystal

Our results lead to the following conclusions.

Electronic structures and optical properties of Zn-doped β-Ga2O3 with different doping sites

<正>The electronic structures and optical properties of intrinsicβ-Ga₂O₃ and Zn-dopedβ-Ga₂O₃ are investigated by first-principles calculations.The analysis about the thermal stability shows that Zn-dopedβ-Ga₂O₃ remains stable. The Zn doping does not change the basic electronic structure ofβ-Ga₂O₃,but only generates an empty energy level above the maximum of the valence band,which is shallow enough to make the Zn-dopedβ-Ga₂O₃ a typical p-type semiconductor.Because of Zn doping,absorption and reflectivity are enhanced in the near infrared region.The higher absorption and reflectivity of Zn_Ca（2） than those of Zn_Ca（1）are due to more empty energy states of Zn_Ca（2）than those of Zn_Ca（1） near E_f in the near infrared region.     

Synthesis by sol–gel process,structural and optical properties of nanoparticles of zinc oxide doped vanadium

We report the elaboration of vanadium-doped ZnO nanoparticles prepared by a sol–gel processing technique. In our approach, the water for hydrolysis was slowly released by esterification reaction followed by a supercritical drying in ethyl alcohol. Vanadium doping concentration of 10 at.% has been investigated. After treatment in air at different temperatures, the obtained nanopowder was characterised by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL). Analysis by scanning electron microscopy at high resolution shows that the grain size increases with increasing temperature. Thus, in the case of thermal treatment at 500 °C in air, the powder with an average particle size of 25 nm shows a strong luminescence band in the visible range. The intensity and energy position of the obtained PL band depends on the temperature measurement increase. The mechanism of this emission band is discussed.     

Characteristics of a new-type SHG crystala β-BaB2O4 in the femtosecond region

The optical characteristics of a new nonlinear crystal β-BaB₂O₄, including the group-velocity dispersion and the nonlinear coefficient in the femtosecond region, are investigated through the second-harmonic generation (SGH). The performances of β-BaB₂O₄ relative to KDP are evaluated from both calculations and measurements. From the measurements using the crystals with different thicknesses, the influence of the group-velocity mismatch of β-BaB₂O₄ on the broadening of the correlation width is revealed, and is found to be smaller than that of KDP. Overall performance of the SHG conversion efficiency of β-BaB₂O₄ including all affecting factors is evaluated to show higher values by a factor of 10 to 10² than that of KDP depending on operating conditions.     

Structural and optical properties of N-doped β-Ga2O3 films deposited by RF magnetron sputtering

The N-doped β-Ga₂O₃ ?lms were grown on Si and quartz substrates by RF magnetron sputtering in different ammonia partial pressure ratios (from 0% to 30%). The influence of ammonia partial pressure ratios and annealing treatment on the optical and structural properties were studied. The microstructure, optical transmittance, optical absorption and optical energy gap of the N-doped β-Ga₂O₃ films are significantly changed with the increasing of ammonia partial pressure. The green, blue and ultraviolet emission bands are observed and discussed.     

EPR Study of Nd3☎ Ions in β-BaB2O4 Single Crystals

An Electron Paramagnetic Resonance (EPR) study of Nd^3? ions in single crystals of the low-temperature phase of barium borate (β-BaB₂O₄ or BBO) is presented. The EPR spectra show the existence of a minimum of three different Nd^3? centres. The g-matrices for three of the centres have been determined from the analysis of the angular dependencies of the spectrum in two planes of the crystal. This study allows us to conclude that neodymium is incorporated in the low-symmetry Ba^2? site. Possible reasons for the appearance of various Nd^3? centres are discussed.     

Spin-spin interaction of Ni2+ ions in ZnSiF6·6H2O

The angular dependences of the electron spin resonance spectrum of 1% Ni²⁺ ions in a ZnSiF₆·6H₂O matrix are investigated experimentally at 36 GHz and 4.2 K. Besides the main spectrum of the isolated ion, we observed a spectrum due to interacting pairs of Ni²⁺ ions, located in the first (nn) and second (2n) coordination spheres and coupled by, besides the magnetic dipole-dipole interaction, isotropic exchange: J _nn = (−197±1)×10⁻⁴, J _2nα = (−5±1)×10⁻⁴, and J _2nβ = (3±2)×10⁻⁴ cm⁻¹. Lines due to other isolated Ni²⁺ ions, which have a different initial splitting D, are also present in the spectrum with intensity comparable to the pair spectrum. Low-symmetry distortions of the crystal field are observed, caused by a pair of impurity ions located close to one another. It is shown that the previously proposed interpretation is incorrect. Fiz. Tverd. Tela (St. Petersburg) 41, 1602–1608 (September 1999)     

Effects of heat treatment and TiO2 content on the optical properties of Eu3+ doped TiO2–SiO2 thin films

The photoluminescence properties of Eu³⁺-doped TiO₂–SiO₂ thin films were investigated. The films were deposited on silicon substrates by the sol–gel process using the dip-coating method. The molar ratio of TiO₂ content was varied from 25% to 100%, while Europium concentration was fixed to 1%. The obtained films were calcinated at various temperatures ranging from 400 °C to 1300 °C, which allowed determining the optimal conditions for the Eu³⁺ luminescence. Meanwhile, the structure of TiO₂–SiO₂ powders, prepared in the same conditions as the films, was also studied by Raman spectroscopy. It revealed the role of Europium and SiO₂ on the stabilization of the anatase phase and the importance of the silica matrix in the control of titania particle size.     

Spectral dispersion of linear optical properties for Sm2O3 doped B2O3–PbO–Al2O3 glasses

Glasses having composition (B₂O₃)₂₅ (PbO)₇₀ (Al₂O₃)₅ (Sm₂O₃)_x ,where x=0, 0.5, 1, 2, 3 and 5 g were prepared using the normal melt quench technique. Spectral reflectance and transmittance at normal incidence of the glass samples are recorded with a spectrophotometer in the spectral range 220–2200 nm. These measured values are introduced into analytical expressions to calculate the real and imaginary parts of the refractive indices. Wemple–DiDomenico single oscillator model and one-term Sellmeier dispersion relations are used to model the real refractive indices. Dispersion parameters such as: single oscillator energy, dispersion energy, lattice oscillating strength, average oscillator wavelength, average oscillator strength and Abbe's number are deduced and compared. Absorption dispersion parameters such as: Fermi energy, optical energy gap for direct and indirect transitions, Urbach energy and steepness parameter are calculated. Effects of doping Sm₂O₃ on these linear optical parameters are investigated and interpreted.     

Generation of continuous-wave coherent radiation tunable down to 190.8nm in β-BaB2O4

Continuous-wave coherent radiation tunable in the wavelength range 190.8–196.1 nm has been generated by sum-frequency generation in -BaB₂O₄. The fundamental beams were supplied by a Ti:Al₂O₃ laser and a frequency-doubled argon-ion laser.     

Synthesis and magnetic properties of Co–Zn magnetic fluid

Co_1−xZn_xFe₂O₄ (with x varying from 0 to 0.7) nanoparticles to be used for ferrofluid preparation were prepared by chemical co-precipitation method. The fine particles were suitably dispersed in transformer oil using oleic acid as the surfactant. The magnetization (M_s) and the size of the particles were measured at room temperature. The magnetization (M_s) was found to decrease with the increase in zinc substitution. The magnetic particle size (D_m) of the fluid was found to vary from 11.19 to 4.25 nm decreasing with the increase in zinc substitution.