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.     

Near-infrared downconversion in Ce<Superscript>3+</Superscript>–Yb<Superscript>3+</Superscript> co-doped YAG

The phosphors YAG co-doped with Ce³⁺–Yb³⁺ ion pair were successfully synthesized by solid state reaction method varying the concentration of Yb³⁺ ions from 1 to 15 % mol. The phosphors were characterized by powder X-ray powder diffraction and surface morphology was studied by scanning electronic microscope. The photoluminescence (PL) properties were studied by spectrophotometers in near infra red (NIR) and ultra violet visible region. The synthesized phosphors can convert a photon of blue region (469 nm) into photons of NIR region (979 and 992 nm). The co-operative energy transfer was studied by time decay curve and PL spectra. The theoretical value of quantum efficiency was calculated from steady time decay measurement and the maximum efficiency approached up to 145.19 %. Hence this phosphor could be used as a downconversion luminescent convertor in front of crystalline silicon solar cell (c-Si) panels to reduce thermalization loss due to spectral mismatch of the solar cells.     

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.     

Sol–gel combustion synthesis of nanocrystalline LaMnO<Subscript>3</Subscript> powders and photocatalystic properties

A novel LaMnO₃ photocatalyst with perovskite structure was prepared by sol–gel combustion method. The combustion reaction mechanisms of nanocrystalline LaMnO₃ powders were investigated by thermal analysis, infrared spectra, and X-ray diffraction technique. The results showed that the gels exhibited self-propagating behavior after ignition in air. Nanocrystalline LaMnO₃ powders can be synthesized in one step by using sol–gel combustion synthesis. The photocatalytic activity of the LaMnO₃ powders were evaluated by degradation of methyl orange (MO) in water under UV light irradiation. The results showed that the LaMnO₃ powders exhibit good photocatalytic activities under UV light irradiation. The degradation percentage after 36 h on LaMnO₃ powders was about 76%.     

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.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Photoluminescence of Eu<Superscript>3+</Superscript> ion in SnO<Subscript>2</Subscript> obtained by sol–gel

Photoluminescence data of Eu-doped SnO₂ xerogels are presented, yielding information on the symmetry of Eu³⁺ luminescent centers, which can be related to their location in the matrix: at lattice sites, substituting to Sn⁴⁺, or segregated at particles surface. Influence of doping concentration and/or particle size on the photoluminescence spectra obtained by energy transfer from the matrix to Eu³⁺ sites is investigated. Results show that a better efficiency in the energy transfer processes is obtained for high symmetry Eu³⁺ sites and low doping levels. Emission intensity from ⁵D₀→⁷F₁ transition increases as the temperature is raised from 10 to 240 K, under excitation at 266 nm laser line, because in this transition the multiphonon emission becomes significant only above 240 K. As an extension of this result, we predict high effectiveness for room temperature operation of Eu-based optical communication devices. X-ray diffraction data show that the impurity excess inhibits particle growth, which may influence the asymmetry ratio of luminescence spectra.     

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.     

Mechanism of grain growth and excellent polarization,dielectric relaxtion of La<Superscript>3+</Superscript>, Nd<Superscript>3+</Superscript> modified PZT nano-films prepared by sol–gel technique

Ferroelectric PbZr_0.52Ti_0.48O₃ film and its partial substitutions by rare earth ions La³⁺ and Nd³⁺ Pb_0.9(La/Nd)_0.1Zr_0.52Ti_0.48O₃, grown on Pt(111)/Ti/SiO₂/Si(100) substrates, were prepared via sol–gel and rapid thermal processes. Structural characterization by X-ray diffraction and scanning electron microscopy showed that Pb(Zr_0.52Ti_0.48)O₃ and Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ films are of (111) preferred orientation but Pb_0.9Nd_0.1(Zr_0.52Ti_0.48)O₃ is more inclined to (100) reflection though both are of tetragonal perovskite structure. The results indicate that the piezoelectric properties of PZT thin films can be improved by doping La³⁺ and Nd³⁺ substituted A-site. The d₃₃ can be dramatically improved by doping La³⁺. Moreover, Pr of Pb(Zr_0.52Ti_0.48)O₃ films reaches up to 120.53 µC/cm², while the doping samples present relatively inferior ferroelectric hysteresis loops (Pr_La?=?64.32, Pr_Nd?=?53.17 µC/cm²), greater dielectric constants, higher dielectric loss and lower leakage current than the undoped Pb(Zr_0.52Ti_0.48)O₃ sample. And meanwhile, the samples showed a typical non-Debye dielectric spectroscopy of multiple quantum relaxation time distribution observing from the Cole–Cole plot at room temperature.     

Sol–gel preparation and luminescence of RE<Subscript>3</Subscript>BO<Subscript>6</Subscript>: Dy<Superscript>3+</Superscript> (RE = La,Y, Gd) microparticles with hybrid precursors

Dysprosium ion activated RE₃BO₆ (RE = La, Y, Gd) polycrystalline phosphors have been prepared via a modified sol–gel process with urea as fuel and rare earth nitrates as precursors. The crystal phase and the morphology of the phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average particle size after heat treatment at 1,000 °C is around 5 μm by particle size determination technique. The characteristic transitions of Dy³⁺ due to ⁴F_9/2 → ⁶H_15/2 (blue) and ⁴F_9/2. → ⁶H_13/2 (yellow) can be observed in the emission spectra and the yellow-to-blue intensity ratio (Y/B) can be changed with the variety of the doped concentration of Dy³⁺ ion. Zeta potential shows the relationship between the surface charges to the pH value in suspension.     

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.     

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.     

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.     

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.     

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.     

Controllable synthesis and luminescence of YPO<Subscript>4</Subscript>:Ln<Superscript>3+</Superscript> (Ln = Eu and Sm) nanotubes

YPO₄:Ln³⁺ (Ln = Eu and Sm) nanotubes were synthesized by a precipitation process in the presence of SDS. The XRD results showed that all samples have a xenotime type tetragonal structure, indicating that doped rare earth ions have no influence on the phase. The SEM and TEM images showed that all samples are nanotubes. On basis of the morphology of samples and the properties of SDS, the possible formation mechanism was speculated. YPO₄:Eu³⁺ and YPO₄:Sm³⁺ nanotubes showed characteristic emission bands of Eu³⁺ and Sm³⁺ ions, respectively. For YPO₄:Eu³⁺/Sm³⁺ nanotubes, the codoping Sm³⁺ ions can enhance the emission intensity of Eu³⁺ ions.     

Luminous properties of skin–core structure new luminous fiber: SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>,Dy<Superscript>3+</Superscript>-PET/light conversion agent-PET

SrAl₂O₄:Eu²⁺,Dy³⁺-polyethylene terephthalate (PET)/light conversion agent-PET, which is a new skin–core structure luminous fiber that can emit red light in the darkness, was fabricated by melt spinning with the combination of light conversion agent-PET and SrAl₂O₄:Eu²⁺,Dy³⁺-PET. An energy transfer occurred between SrAl₂O₄:Eu²⁺,Dy³⁺ and light conversion agent, and the light conversion agent emitted red light absorbed from SrAl₂O₄:Eu²⁺,Dy³⁺. To investigate the effect of light conversion agent on the luminous properties of SrAl₂O₄:Eu²⁺,Dy³⁺-PET-light conversion agent, several kinds of luminous fiber that contained different light conversion agents were artificially manufactured and their luminous properties were investigated. Results showed that under near-ultraviolet excitation, the fluorescent color of luminous fiber was primarily located in the orange-red area, with more intense red color than the others.     

Effects of pH and concentration on ability of Cl<Superscript>−</Superscript> and NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> to intercalate into a hydrotalcite-like compound during its synthesis

In this study, we confirmed that the characteristics of anion intercalation into the interlayer of a hydrotalcite-like compound (HT) during synthesis are similar to those of the anion-exchange reaction of HTs as well as the reconstruction reaction of HTs from Mg-Al oxide. We demonstrated that (i) Cl⁻, which has a higher charge density than NO₃⁻, more easily reacted with Mg and Al species to form HT structure, resulting in greater intercalation of Cl⁻ into the HT interlayer; and (ii) for HTs with lower Mg: Al molar ratios, OH⁻, which has a higher charge density than Cl⁻ and NO₃⁻, was more likely to interact with Mg and Al species to form HT structure, blocking the intercalation of Cl⁻ and NO₃⁻. Furthermore, we showed that high concentrations of Cl⁻ and NO₃⁻ in solution regulated their intercalation into the HT interlayer. The high activity of Cl⁻ and NO₃⁻ in solution would facilitate the anions’ reactions with Mg and Al species to form HTs, resulting in a high degree of anion intercalation into the interlayer of HTs.     

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.