Pure Monoclinic Phase Research Articles

Luminescence of Tb-doped Ca 3Y 2(Si 3O 9) 2 oxide upon UV and VUV synchrotron radiation excitation

Powders of calcium yttrium silicate, Ca 3Y 2(Si 3O 9) 2, containing 0.1–3% Tb 3+ were prepared using a sol-gel method and characterized with XRD, IR, UV–vis and UV–VUV spectroscopies at room temperature and 10 K. Structural analysis revealed pure monoclinic phase of Ca 3Y 2(Si 3O 9) 2 after heat-treatment at 1000 °C. Infrared spectroscopy showed that between 800 and 900 °C a short-range structural organization of the components proceeded, yet without crystallization. A strong emission of Tb 3+ had been observed both in the green part of the spectrum due to the 5 D 4→ 7 F J transitions and in the blue-violet region owing to the 5 D 3→ 7 F J radiative relaxation. The color of the light could be tuned from yellowish-green to bluish-white both by means of the dopant content and the temperature of synthesis. Efficient luminescence of Tb 3+-doped Ca 3Y 2(Si 3O 9) 2 phosphors could also be obtained upon stimulation with vacuum ultraviolet synchrotron radiation demonstrating that an energy transfer from the host to the Tb 3+ ions takes place.

Synthesis and Characterization of SrAl2O4:Eu2+, Dy3+ Nanocrystalline Phosphorescent Pigments

In this research, the Eu2+ and Dy3+ co-doped strontium aluminate (SrAl2O4) nanocrystalline phosphorescent pigments with high brightness and long afterglow was successfully synthesized by urea-nitrate solution combustion method (SCS) at 600°C, followed by heating the resultant combustion ash at 1200°C in an atmosphere which was weak reducing (5%H2 + 95%N2). The pure SrAl2O4 monoclinic phase as host structure could be formed by combustion method in which the temperature is very much lower than solid-state method. A broad-band UV-excited luminescence of the SrAl2O4:Eu2+, Dy3+ phosphorescent pigments was observed at λmax = 517 nm due to transitions from 4f65d1 to 4f7 configuration of the emission center (Eu2+ ions). The excitation spectra showed two main peaks at 240 and 256 nm. Eventually, the average grain size of the combustion ash powder and SrAl2O4:Eu2+, Dy3+ phosphor particles were obtained as 40 and 62 nm, respectively via Scherrer’s formula and these particles were in thin flake form.

Soft Synthesis Route and Characterization of Superparamagnetic Mn1/2Fe1/2(H2PO4)2·2H2O and Its Decomposed Product

The superparamagnetic Mn1/2Fe1/2(H2PO4)2·2H2O was synthesized by a soft synthesis method using a Mn(c)−Fe(c)−H3PO4 system in water−acetone medium at ambient temperature. The synthesized Mn1/2Fe1/2(H2PO4)2·2H2O decomposed through the dehydration and the phosphate condensation reactions at high temperature and yielded binary manganese iron cyclotetraphosphate MnFeP4O12. The XRD and FTIR results of the synthesized Mn1/2Fe1/2(H2PO4)2·2H2O and the decomposed MnFeP4O12 indicate the pure monoclinic phase with space group P21/n and C2/c, respectively. The thermal behaviors and superparamagnetic properties of Mn1/2Fe1/2(H2PO4)2·2H2O and MnFeP4O12 in this work differed from the single compounds (M(H2PO4)2·2H2O and M2P4O12, where M = Mn, Fe) and the binary compounds (Mn0.5Fe0.5(H2PO4)2·xH2O) reported in previous works. The kinetic and thermodynamic functions for thermal decomposition of Mn1/2Fe1/2(H2PO4)2·2H2O were studied and confirmed as reaction mechanisms. Vibrational frequencies of breaking bonds in two thermal...

Luminescent Properties of Ba2(Mg, Zn)Si2O7:Eu2+ Particles as Potential Blue-Green Phosphors For Ultraviolet Light-Emitting Diodes

Ba2−xMg1−yZnySi2O7:Eux2+ blue–green phosphor particles were prepared by combustion-assisted synthesis method as the fluorescent material for ultraviolet light-emitting diodes (UV-LEDs), performing as a light source. The luminescent properties were investigated by changing the postannealing temperature, the concentration of the activator, and the ratio of Zn to Mg. The crystallinity and luminescence were investigated by using an X-ray diffractometer and a luminescence spectrometer. The pure monoclinic Ba2MgSi2O7 and Ba2ZnSi2O7 phases were formed when the posttreatment temperature was 1000°C. It was found that the introduction of Zn2+ into Ba2MgSi2O7:Eu2+ effectively increased its emission. The emission spectra presented an emission position red shift of up to 5 nm from Ba2Mg Si2O7:Eu2+ to Ba2ZnSi2O7:Eu2+, which is correlated with the effect of Zn2+ substituting for Mg2+ sites. The excitation spectrum of Ba2ZnSi2O7:Eu2+ was a broad-band extending from 260 to 465 nm, which matches the emission of UV-LEDs.

A simple synthesis and characterization of binary Co 0.5Fe 0.5(H 2PO 4) 2·2H 2O and its final decomposition product CoFeP 4O 12

This paper reports the synthesis of binary Co 0.5Fe 0.5(H 2PO 4) 2·2H 2O by a simple, rapid and cost-effective method using CoCO 3–Fe(c)–H 3PO 4 system in water–acetone media at ambient temperature. Thermal transformation of the synthesized powder was investigated by TG/DTG/DTA and DSC techniques, which indicate that its final decomposed product was a binary cobalt iron cyclotetraphosphate CoFeP 4O 12. The FTIR and XRD results of the synthesized Co 0.5Fe 0.5(H 2PO 4) 2·2H 2O and the decomposed CoFeP 4O 12 indicate the pure monoclinic phases with space group P2 1/n and C2/c, respectively. The morphologies of Co 0.5Fe 0.5(H 2PO 4) 2·2H 2O and CoFeP 4O 12 powders appear non-uniform particle shapes and high agglomerates, which are different from the cases of the single compounds M(H 2PO 4) 2·2H 2O and M 2P 4O 12 (where M = Co, Fe). The magnetic properties of the studied compounds are superparamagnetic behaviors, which are important for specific applications. The physical properties of the studied powders are comparable with those reported in our previous study, affected by medium and condition of preparation method.

Hydrothermal Synthesis, Microstructure and Photoluminescence of Eu-Doped Mixed Rare Earth Nano-Orthophosphates.

Eu3+-doped mixed rare earth orthophosphates (rare earth = La, Y, Gd) have been prepared by hydrothermal technology, whose crystal phase and microstructure both vary with the molar ratio of the mixed rare earth ions. For LaxY1–xPO4: Eu3+, the ion radius distinction between the La3+ and Y3+ is so large that only La0.9Y0.1PO4: Eu3+ shows the pure monoclinic phase. For LaxGd1–xPO4: Eu3+ system, with the increase in the La content, the crystal phase structure of the product changes from the hexagonal phase to the monoclinic phase and the microstructure of them changes from the nanorods to nanowires. Similarly, YxGd1–xPO4: Eu3+, Y0.1Gd0.9PO4: Eu3+ and Y0.5Gd0.5PO4: Eu3+ samples present the pure hexagonal phase and nanorods microstructure, while Y0.9Gd0.1PO4: Eu3+ exhibits the tetragonal phase and nanocubic micromorphology. The photoluminescence behaviors of Eu3+ in these hosts are strongly related to the nature of the host (composition, crystal phase and microstructure).

Grass blade-like microparticle MnPO 4·H 2O prepared by a simple precipitation at room temperature

Grass blade-like microparticle MnPO 4·H 2O was synthesized by a simple precipitation at room temperature using a mixture of manganese sulphate monohydrate, phosphoric acid and water at pH = 7. The thermogravimetric study indicates that the synthesized compound is stable below 500 °C and its final decomposed product is Mn 2P 2O 7. The pure monoclinic phases of the synthesized MnPO 4·H 2O and its final decomposed product Mn 2P 2O 7 are verified by XRD data. FTIR spectra indicate the presences of the PO 4 3− ion and water molecules in the MnPO 4·H 2O structure and the P 2O 7 4− ion in the Mn 2P 2O 7 structure. The thermal stability, crystallite size, and grass blade-like microparticle of MnPO 4·H 2O in this work are different from previous reports, which may be caused by the starting reagents and reaction condition for the precipitation.

Atmospheric pressure chemical vapour deposition and characterisation of crystalline InTaO4, InNbO4 and InVO4 coatings

Abstract The possibilities to grow crystalline complex InTaO 4 , InNbO 4 and InVO 4 coatings as well as single oxide layers In 2 O 3 , Ta 2 O 5 , Nb 2 O 5 , and VO x were investigated using aerosol assisted atmospheric pressure chemical vapour deposition technique. Indium(III) and niobium(IV) tetramethylheptanedionates, tantalum(V) tetraethoxyacethylacetonate and vanadium(III) acethylacetonate were used as precursors, monoglyme and toluene as solvents. The influence of deposition conditions and solution composition on elemental and phase compositions of layers was studied. Indium tantalate layers containing pure monoclinic InTaO 4 phase were obtained ex-situ, i.e., after high-temperature (800 °C) annealing of layers grown at lower temperature (500 °C). Films containing pure orthorhombic indium vanadate or monoclinic indium niobate phase may be prepared using both in-situ (600 °C) or ex-situ (deposition at 400 °C, annealing at 800 °C) approaches. Under optimised deposition conditions and solution compositions, Ni-doped InVO 4 and InTaO 4 films were also deposited and their photocatalytic activity was tested.

Synthesis and CO2 Adsorption Characteristics of Lithium Zirconates with High Lithia Content

Pure monoclinic phase Li6Zr2O7 and rhombohedral phase Li8ZrO6 that coexisted with a fraction of Li6Zr2O7, are synthesized by a liquid phase coprecipitation method and characterized by X‐ray diffraction, scanning electron microscopy, and thermo‐gravimetric analysis. The high‐temperature CO2 uptake properties of both samples are systematically investigated. The temperature effect tests indicate that, in the case of low temperature (<973 K), both of the adsorbents exhibit slow CO2 uptake rates because of the inhibited diffusion of CO2 in the solid carbonate shell; while at the temperature above the melting point of Li2CO3 (about 983 K), the CO2 uptake rates are enhanced dramatically for both Li6Zr2O7 and Li8ZrO6, and achieved about 12.3% weight gain and 35.0% weight gain within 15 min at 1073 K, respectively. The thermal stability tests indicate that both samples exhibit gradually reduced capacities during the multicycle processes. The analysis of the crystalline structure reveals that the reduced capacities are resulted from the loss of lithia under high temperatures. Finally, the possible adsorption pathways for both monoclinic phase Li6Zr2O7 and rhombohedral phase Li8ZrO6 are suggested as well.

Photoluminescence of cubic and monoclinic Gd 2O 3:Eu phosphors prepared by flame spray pyrolysis

In this paper, europium-doped gadolinium phosphor, which is a potentially bifunctional material with both fluorescent and magnetic properties, has been prepared in a one-step procedure via flame spray pyrolysis, and its crystal structure, morphology, and PL intensity were investigated. All the prepared phosphors were submicron-sized with spherical shapes and either a pure cubic or pure monoclinic phase. In order to observe the effects of temperature on the crystal phases of the prepared phosphors, we applied a H 2 vs. N 2/O 2 diffusion flame, with the maximum flame temperature ranging from T max=1375 to 2050 K. The temperature profiles under various flame conditions are also reported herein to further elucidate the rapid synthesis process. The PL intensity in the cubic phase improved linearly with increasing flame temperature until the transition to a monoclinic phase. The peak of the photoluminescence(PL) spectrum from the phosphors prepared at T max=1733 K in the cubic phase was narrower and twice as strong as the peak of the PL spectrum from the phosphors prepared at T max=2050 K in the monoclinic phase. This paper provides important data showing the relationship between the synthesis temperature and the phase transition in Gd 2O 3:Eu in the continuous one-step use of flame spray pyrolysis.

Sol–gel preparation and photoluminescence enhancement of Li + and Eu 3+ co-doped YPO 4 nanophosphors

YPO 4 nanoparticles with pure monoclinic phase were successfully synthesized by a simple sol–gel method using both citric acid (CA) and ethylene diamine tetraacetic acid (EDTA) as complexing agent. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as high-resolution transmission electron microscopy (HRTEM) have been employed to characterize the as-synthesized nanoparticles. Furthermore, the photoluminescence (PL) characterization of the Li + and Eu 3+ co-doped YPO 4 nanocrystals was carried out and the effects of the doping concentration of Li + and Eu 3+ active center concentration as well as calcination temperature on the PL properties have been studied in details. The results show that the incorporation of Li + ions into the YPO 4:Eu 3+ lattice could induce a remarkable improvement of the PL intensity. The highest emission intensity was observed with the compound of 5%Li + and 5%Eu 3+ co-doped YPO 4, whose brightness was increased by a factor of more than 2.5 in comparison with that of the YPO 4:5%Eu.

Selective Growth of Monoclinic and Tetragonal Zirconia Nanocrystals

The growth of metal oxide nanocrystals with a well-organized crystalline phase is of fundamental and technological interest because in this way it is possible to tune their size-dependent unique properties. In this communication, we demonstrate the selective growth of monoclinic and tetragonal ZrO(2) nanocrystals of <10 nm diameter driven by controlling the surface energy, with and without capping by N(CH(3))(4)(+). The nanocrystals were grown in aqueous solution at 150 degrees C. It was revealed, by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and optical absorption studies, that the nanocrystals capped by N(CH(3))(4)(+) have a less defective pure monoclinic phase, while those without capping have a pure tetragonal phase with highly disordered oxygen vacancies. The N(CH(3))(4)(+) capping on the surface oxygen site can reduce the surface energy low enough to stabilize the monoclinic phase. By contrast, the bare surface oxygen site has higher energy; thereby, the lower surface energy tetragonal phase is formed spontaneously. The present concept is a promising universal approach to control the crystal phases of technologically important oxide nanocrystals.

Large Scale Synthesis of Shuttle like CuO Nanocrystals by Microwave Irradiation

Nanocrystalline CuO with shuttle-morphology has been prepared conventionally by a microwave irradiation heating technique from an aqueous system in the presence of Cu(CH3COO)2• H2O and NaOH at room temperature. The X-ray powder diffraction pattern indicates that the product is indicated that the product was pure monoclinic phase of CuO. Further characterized by transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy and Raman spectra, the component of the products were confirmed.

One-step thermal synthesis of binary manganese iron cyclotetraphosphate MnFeP4O12

The manganese iron cyclotetraphosphate (MnFeP4O12) was synthesized through one-step thermal synthesis at 700 °C using the mixing of manganese and iron metals and phosphoric acid in the presence of water–acetone media. Both FTIR and XRD results indicate the cyclotetraphosphate (P4O124−) structure and a pure monoclinic phase with space group C2/c (Z = 4). The morphology and crystallite size for the MnFeP4O12 obtained from SEM data and X-ray line broadening show non-uniform particles and 30 ± 9 nm, respectively. The magnetic study of the synthesized MnFeP4O12 shows superparamagnetic behavior, which is important for specific application. Some physical properties of the synthesized MnFeP4O12 powder presented for the first time are comparable with those from individual M2P4O12 (M = Mn and Fe) and a binary metal compound as CoFeP4O12.

Synthesis and ferromagnetic property of new binary copper iron pyrophosphate CuFeP 2O 7

The pyrophosphate of CuFeP 2O 7 was synthesized through one step-thermal synthesis at 500 °C using the mixing of copper carbonate, iron metals and phosphoric acid. FTIR and XRD results indicate the dominant feature of pyrophosphate (P 2O 7 4−) anion and a pure monoclinic phase with space group C 2h 6 ( Z = 4), respectively. The crystallite size of 25 ± 9 nm for the CuFeP 2O 7 was estimated by X-ray line broadening. Room temperature magnetization result shows ferromagnetic behavior of the CuFeP 2O 7 powder, having hysteresis loop in the range of ± 10,000 Oe with the specific magnetization value of 1.57 emu g − 1 . This property is important for specific application and is presented for the first time.

Floral-like microarchitectures of cobalt iron cyclotetraphosphate obtained by solid state synthesis

Abstract Floral-like microparticle of a binary cobalt iron cyclotetraphosphate CoFeP 4 O 12 was synthesized through solid phase reaction using cobalt carbonate, iron metal and phosphoric acid with further calcinations at the temperature of 500 °C. The XRD and FTIR results indicate that the prepared CoFeP 4 O 12 has a pure monoclinic phase without the presence of any phase impurities. The floral-like microparticle and superparamagnetic behavior of the synthesized CoFeP 4 O 12 are important properties for specific applications, which were revealed by SEM and VSM techniques, respectively. The dominant features of the synthesized CoFeP 4 O 12 in this work are compared with M 2 P 4 O 12 (M = Co and Fe) and CoFeP 4 O 12 reported in our previous works.

Ferroelectric properties of highly (1 1 1)-oriented Pb(Zr 1− x, Ti x)O 3 thin films with different Zr/Ti ratios

Pb(Zr 1− x , Ti x )O 3 thin films with different Zr/Ti ratios (0.45 ≤ x ≤ 0.49) were prepared by a sol–gel method using nitrate zirconium as starting material and 2-methoxyethanol as solvent. The films were deposited on Pt (1 1 1)/Ti/SiO 2/Si (1 0 0) substrates by spin-coating process and annealed at 650 °C for 3 min by rapid thermal annealing (RTA). X-ray diffraction (XRD) revealed that the films crystallized in perovskite phase and were all (1 1 1)-oriented. The effect of Zr/Ti ratios on the phase components and ferroelectric properties of the thin films was investigated. The result suggests that monoclinic phase and tetragonal phase coexists for the films with 0.47 ≤ x ≤ 0.49 and there is a pure monoclinic phase for the films with x ≤ 0.46. The films with x ≤ 0.46 exhibit higher remnant polarizations ( 2 P r max = 44.9 μ C/c m 2 ) compared with the other films, as is explained by more monoclinic phase content and higher (1 1 1) orientation degree.

Controlled Hydrothermal Synthesis of Zirconium Oxide Nanostructures and Their Optical Properties

Zirconium oxide (ZrO2 or zirconia) nanostructures were synthesized by a hydrothermal route. Surface morphology analysis depicts the formation of various zirconia nanostructures at different synthesis conditions. X-ray diffraction examination demonstrates that the as-synthesized zirconia is of pure monoclinic phase (m-ZrO2). High resolution transmission electron microscopy (HRTEM) further confirms the high crystalline feature of the m-ZrO2 nanostructures. X-ray photoelectron spectroscopy (XPS) core-level spectra of Zr 3d and O 1s for the ZrO2 nanostructures have been studied to understand further the electronic states and chemical environment of the Zr and O atoms in ZrO2 for different synthesis conditions. XPS results also indicate the existence of oxygen defects and zirconia suboxides which affect the structural and optical properties of zirconia nanostructures. The nanostructures show UV−vis absorption band around 290 nm at room temperature. The band gap energy is determined, in the range of 2.5−3.8 eV for zirconia nanostructures synthesized at various conditions. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of zirconia nanostructures at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancy in the material.

Low-temperature molten salt synthesis and characterization of CoWO 4 nano-particles

CoWO 4 nano-particles were successfully synthesized at a low temperature of 270 °C by a molten salt method, and effects of such processing parameters as holding time and salt quantity on the crystallization and development of CoWO 4 crystallites were initially studied. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescent spectra techniques (PL), respectively. Experimental results showed that the well-crystallized CoWO 4 nano-particles with ca. 45 nm in diameter could be obtained at 270 °C for a holding time of 8 h with 6:1 mass ratio of the salt to CoWO 4 precursor, and XRD analysis evidenced that the as-prepared sample was a pure monoclinic phase of CoWO 4 with wolframite structure. Their PL spectra revealed that the CoWO 4 nano-particles displayed a very strong PL peak at 453 nm with the excitation wavelength of 230 nm, and PL properties of CoWO 4 crystallites relied on their crystalline state, especially on their particle size.

Structure dependence of near-infrared stimulated blue emission in polycrystalline Ln 2(WO 4) 3 (Ln=Gd and Lu) doped with Tm and Yb

Tm- and Yb-doped gadolinium tungstate, (Gd x Tm y Yb 1− x − y ) 2(WO 4) 3 ( x=0.7–0.9; y=0.001–0.01), have been prepared by the polymerized complex method to achieve a homogeneous dispersion of dopants and to stabilize the host structure. Decomposition (900 °C 5 h) of the precursors with x=0.8–0.9 yielded a pure monoclinic phase, while that of x=0.7 resulted in formation of an orthorhombic impurity. The monoclinic phase exhibits bright up-converted blue emission due to the 1G 4→ 3H 6 transition of Tm 3+ (472 nm) upon excitation into the Yb 3+: 2F 7/2→ 2F 5/2 absorption band as a result of energy transfer from Yb to Tm. The orthorhombic impurity acts as a strong quencher of emission, and the quenching mechanism has been discussed on the basis of structural and spectroscopic properties of orthorhombic Lu 2(WO 4) 3:Tm,Yb prepared by the same method.