Polymer Complex Solution Method Research Articles

Photoluminescence of europium(III)-doped (YxSc1−x)2O3 nanoparticles: Linear relationship between structural and emission properties

Europium (III)-doped (YxSc1−x)2O3 nanocrystalline powders of different compositions (x=0, 0.25, 0.5, 0.75 and 1) are synthesized using a polymer complex solution method. Comparative structural and optical characterization is carried out with powder X-ray diffraction and photoluminescence excitation, emission and emission decay measurements. Detailed information about unit cell parameter and energy levels of europium (III) ions are presented for all powder compositions. The second rank crystal field parameters (B02) and (B22) and crystal field strength (Nv) are calculated from the energies of Stark components of the 7F1 manifold of the europium (III) emissions. It has been shown that the crystal field parameter changes with the powder composition and shows a linear relationship with the average ionic radii of cations in the solid solutions. A similar dependence is also found for the magnitude of splitting of 7F1 manifold vs. unit cell parameter values. Moreover, this linear relationship is demonstrated for the whole family of europium (III)-doped mixed rare-earth sesquioxide hosts (RR’O3; R, R′=rare earth ions) by taking into consideration results published in the literature so far. A simple, semi-empirical equation which relates structural properties (unit cell parameters, ionic radii) of the sesquioxide host material and the emission properties of europium (III) ions (energy splitting of the 7F1 manifold, crystal field parameters and crystal field strength) are presented.

Europium-doped nanocrystalline Y2O3−La2O3 solid solutions with bixbyite structure

Nanocrystals of Y2O3 and La2O3 solid solutions were synthesized with a cubic bixbyite structure containing La2O3 content of up to 50mol%. This is comparatively higher than that in bulk materials of the same structure, where La2O3 content of only 20mol% can be obtained. A set of europium-doped (Y1−xLax)2O3 (x=0.1, 0.2, 0.3, 0.4) cubic bixbyite solid solutions with crystallites of approximately 10nm in size was prepared using the polymer complex solution method. Structural analysis was performed using X-ray diffraction measurements, Rietveld full profile refinement, and from Eu3+ luminescence emission. The energy levels of the Eu3+ ion, second order crystal field parameters, and crystal field strength were obtained for all compositions of solid solutions. We show that the crystal field parameters linearly depend on unit cell parameter and that these dependencies may be considered as part of an overall dependence for the entire sesquioxide family.

Structural and spectroscopic studies of Eu3+ doped Lu2O3–Gd2O3 solid solutions

A series of europium doped (LuxGd1−x)2O3 (x=1, 0.75, 0.5, 0.25 and 0) nanocrystalline powders were prepared using a polymer complex solution method based on a polyethylene glycol (PEG) as fuel. The samples were systematically characterized by powder X-ray diffraction, scanning and transmission electron microscopies and luminescence spectroscopy. The powders consisted of well-crystalline, cubic phase nanoparticles of 20–50nm in size, which unit cell parameter increased with Gd content complying with Vegard’s law. Upon blue light excitation all samples exhibited strong red luminescence typical of trivalent europium ion. The maximum splitting of the 7F1 manifold changed linearly with the composition change and decreased with lowering of the crystal field strength. Relatively long lifetime values were obtained for 5D0 (∼1.4ms) and 5D1 (∼120μs) levels. For all samples we estimated theoretical densities, refractive index coefficients, optical filling factors and Zeff, in order to estimate the Judd–Ofelt intensity parameters and branching ratios. The calculated lifetime of 5D0 level was in line with experimentally obtained luminescence lifetime values. Relative integrated emissions were measured on all samples and Gd2O3 sample proved to have a maximum amount of the characteristic Eu3+ luminescence.

Comparative structural and photoluminescent study of Eu3+-doped La2O3 and La(OH)3 nanocrystalline powders

Eu3+-doped La2O3 nanocrystalline powder was prepared by polymer complex solution method and further used for preparation of Eu3+-doped La(OH)3. Structural and optical characterization was carried out by powder X-ray diffraction and photoluminescent spectroscopy. XRD measurements confirmed the formation of hexagonal La2O3 and its recrystallization into La(OH)3 in a humid atmosphere. Excitation spectra show redshift of host lattice and charge transfer emission bands in La(OH)3 while bands that correspond to Eu3+f–f transitions are placed at same wavelengths in both samples. Photoluminescence spectra recorded over the temperature range from 10K to 300K show that intensities of emission lines in Eu3+-doped La2O3 do not depend on temperature as much as in La(OH)3 sample. Observed dominant 5D0→7F2 and markedly visible 5D0→7F0 emissions in doped La2O3 indicate that Eu3+ ion is located in a structural site without an inversion center. On the other hand, in Eu3+-doped La(OH)35D0→7F0 transition is barely visible while 5D0→7F2 is not prominent, and with temperature drop three 5D0→7FJ (J=1, 2, 4) transitions become almost of the same intensity. In both La2O3 and La(OH)3 structures Eu3+ ion replaces La3+ in non-centrosymmetric C3v and C3h crystallographic sites, respectively, and difference in symmetry of the crystal field around europium ion is explained by comparing shape and volume of these sites. Decay times of the 5D0- level recorded over the temperature range 10−300K revealed that emission lifetime values in La2O3 (~0.7ms) are almost two times higher than in La(OH)3 (~0.4ms), and unlike in La2O3, lifetime in La(OH)3 is temperature dependent.

Strong emission via up-conversion of Gd2O3:Yb3+, Ho3+ nanopowders co-doped with alkali metals ions

Gadolinium-oxide nanopowders doped with Yb3+ and Ho3+ ions and co-doped with alkali metal ions (Li+ and Na+) were synthesized via the polymer complex solution method and their up-conversion emission properties are analyzed. Prepared powders were well crystallized in cubic bixbyite structure, without any impurity phases and with an average crystallite size of about 25nm, as shown by X-ray powder diffraction analysis. No adsorbed species on the surface of nanoparticles were detected by infrared measurements. The particle morphology was analyzed by transmission electron microscopy, which revealed agglomerated crystalline nanoparticles with irregular, polygonal-like shapes, having a size in the range from 30 to 50nm. Up-conversion emission properties of Gd2O3:Ho3+,Yb3+ nanopowders were evaluated from photoluminescence emission and decay measurements using 980nm excitation. Two-photon up-conversion processes produced emissions in visible – near infrared spectral range, with the strongest green emission from 5F4,5S2→5I8 Ho3+ electronic transition, and weak red and near infrared from 5F5→5I8 and 5F4, 5S2→5I7 transitions, respectively. In addition, three-photon up-conversion emission was detected in ultra-violet–blue spectral region (5G4→5I8, 3D3→5I6 and 5G5→5I8 transitions). Luminescence measurements were performed on samples with different Ho3+ (0.5 and 1at%) and Yb3+ (2, 4 and 6at%) concentrations to find that 0.5at% of Ho3+ and 2at% of Yb3+ provides the most intense up-conversion emission. The influence of alkali metal (Li+ and Na+) ion co-doping is studied on the sample that showed the most intense up-conversion emission. Increase in the intensity of up-conversion emission is observed for both Li+ and Na+ co-doping. The effect is more pronounced with Li+, where addition of 5at% of Li+ led to more than one order of magnitude emission enhancement. Alkali metal ion co-doping also significantly improved up-conversion color purity through considerably larger increase of green emission compared to red and near infrared.

Color-tunable up-conversion emission in Y2O3:Yb3+, Er3+ nanoparticles prepared by polymer complex solution method

Powders of Y2O3 co-doped with Yb3+ and Er3+ composed of well-crystallized nanoparticles (30 to 50 nm in diameter) with no adsorbed ligand species on their surface are prepared by polymer complex solution method. These powders exhibit up-conversion emission upon 978-nm excitation with a color that can be tuned from green to red by changing the Yb3+/Er3+ concentration ratio. The mechanism underlying up-conversion color changes is presented along with material structural and optical properties.PACS42.70.-a, 78.55.Hx, 78.60.-b

Structural and optical investigation of gadolinia-doped ceria powders prepared by polymer complex solution method

Abstract We present a polymer complex solution method using a modified combustion synthesis procedure, for the production of well crystalline, sub-micron gadolinia-doped ceria powders of Ce0.9Gd0.1O1.95 composition. Polyethylene glycol of two different molecular weights (200 and 20000) was used as both fuel for the combustion and nucleating agent for the crystallization process. The synthesized materials were characterized using X-ray diffraction, thermal analysis, scanning electron microscopy, and optical and photoluminescence spectroscopy. The powders are quite similar, fully crystallized in a cubic fluorite-type phase with average crystallite size of about 70 nm and average particle size in the range 220–240 nm. UV-vis absorption spectra show the absorption edge at 3.26 eV. The presence of oxygen vacancies, confirmed indirectly by clear violet emission observed at 428 nm, originated from the 5D1 → 4F1 transition of Ce3+ions.

Dynamic mechanical and thermal properties of the composites of thermoplastic starch and lanthanum hydroxide nanoparticles

AbstractNanostructured lanthanum (III)‐oxide (La2O3) particles were prepared by a polymer complex solution method and further used for the preparation of lanthanum hydroxide (La(OH)3) nanoparticles. The La(OH)3 nanopowder was mixed with glycerol‐plasticized maize starch and the effect of the filler on the thermal, mechanical, and viscoelastic properties of the matrix was investigated. It was expected that this nanofiller, which shows an affinity toward OH groups, would strongly affect the physical properties of thermoplastic starch (TPS). The pure TPS and the TPS‐La(OH)3 nanocomposite films (with 1, 2, and 3 wt % filler) were conditioned at various relative humidities (RHs) (35, 57, 75, and 99% RH). After conditioning at 99% RH, the pure TPS films exhibited higher affinity toward water than the nanocomposites. Differential scanning calorimetric measurements showed that, due to retrogradation effects, the melting enthalpies of the films increased with increasing RH. Dynamic mechanical analysis revealed that the mechanical properties in the linear range strongly depend on both the humidity conditions and the concentration of the filler. The results also show that La(OH)3 nanoparticles are good reinforcement for TPS films. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Thermographic properties of Eu3+ and Sm3+ doped Lu2O3 nanophosphor

The samples, Lu2O3:Eu3+ (3at.% Eu) and Lu2O3:Sm3+ (1at.% Sm), were prepared via polymer complex solution method using polyethlylene-glyocol as the fuel and as nucleation agent for crystallization process. Knowing that lutetium oxide has high chemical stability and temperature resistance, in this paper we investigated possibility for its application in high-temperature phosphor thermometry. It is a non-contact technique that uses the thermal dependence of phosphor fluorescence to measure temperature remotely. The structural and morphological properties were performed through X-ray powder diffraction (XRPD) and transmission electron microscopy (TEM) investigations. The obtained results confirmed that this synthesis yields desired crystalline structure with particle size in the range from 30 to 50 nm. Photoluminescence emission measurements were recorded in the temperature range from room up to 873 K. The accomplished results demonstrate the performance of Eu3+ and Sm3+ doped Lu2O3 as high temperature thermographic phosphors of very good sensitivity.

Fabrication of polycrystalline (Y 0.7Gd 0.3) 2O 3:Eu 3+ ceramics: The influence of initial pressure and sintering temperature on its morphology and photoluminescence activity

Nanocrystalline (Y 0.7Gd 0.3) 2O 3 powder, synthetised via polymer complex solution method, was compacted into 25 pellets applying high pressures (173–867 MPa) for 30 s that were subsequently sintered at different temperatures (800–1400 °C) for 18 h. The morphology and optical characteristics of the starting powder and prepared ceramic samples were monitored and discussed in order to identify the changes induced with the variations of initial compacting pressure, which influence is often neglected, and with sintering temperature. The grain size tends to decrease significantly with increasing pressure, even when elevated temperatures are used for annealing, while low compacting pressure resulted in grain coarsening and, in some cases, even in anomalous morphology of ceramic samples. Luminescence emission in ceramic samples decays faster than in nanopowders, that is in complete agreement with the grain formation and gradual transformation to the bulk material. Judd–Ofelt intensity parameters and branching ratios were calculated taking into account the difference in effective refractive index for nanopowder and ceramic samples.

Preparation of Y 2O 3:Eu 3+ nanopowders via polymer complex solution method and luminescence properties of the sintered ceramics

Herein we presented polymer complex solution method for production of well crystalline europium doped Y 2O 3 nanopowders. Polyethylene glycol (PEG) of five different molecular weights is used both as a fuel and as a nucleation agent for the crystallization. Powders were cold-pressed and sintered to obtain ceramics. SEM images taken from ceramic pellets indicate formation of a dense structure, with a pronounced grain growth and low pore concentration. Luminescence emission spectra of powders and ceramics are similar, and in good agreement with theoretical data. Lifetimes of Eu 3+ 5D 0 level in nanocrystalline powders are higher compared to one observed in bulk, confirming in this case theory of lifetime lengthening in nanophosphors due to the change of effective refraction index. As expected, lifetime values in ceramic samples decrease toward the value in bulk Y 2O 3. The optical filling factor is calculated from observed decay times, providing a measure of discrepancy between powder and bulk state regarding their luminescent properties.

Synthesis and characterization of N-doped TiO 2/ZrO 2 visible light photocatalysts

Zirconia and nitrogen-doped TiO 2 powder was synthesized using a polymer complex solution method for the preparation of an enhanced visible light photocatalyst. The produced catalysts were characterized via the Brunauer, Emmett, and Teller method (BET), X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, and UV–Vis spectrophotometry analyses. The N-doped TiO 2/ZrO 2 photocatalyst showed a high specific surface area and small crystal sizes. The XPS spectra of the N-doped TiO 2/ZrO 2 sample indicated that nitrogen was doped into the TiO 2 lattice and enhanced the photocatalytic activity. The UV–Vis absorption spectra of the N-doped TiO 2/ZrO 2 sample noticeably shifted to the visible light region compared to that of the TiO 2. The photocatalytic activities of the prepared catalysts were evaluated for the decomposition of gaseous NO x under UV and visible light irradiations. The photocatalytic activities of N-doped TiO 2/ZrO 2 were much greater than those of commercial Degussa P25 in both the UV and visible light regions. The high photocatalytic activity can be attributed to stronger absorption in the visible light region, a greater specific surface area, smaller crystal sizes, more surface OH groups, and to the effect of N-doping, which resulted in a lower band gap energy.

Characterization of rare-earth doped Lu 2O 3 nanopowders prepared with polymer complex solution synthesis

We explored a synthesis route based on the polymer complex solution method for the production of the rare-earth doped Lu 2O 3 crystalline nanopowders. In this type of synthesis polyethylene glycol is used both as fuel for the combustion reaction, and as nucleation agent for the crystallization process. Synthesized materials were characterized with X-ray diffraction technique, scanning and transmission electron microscopy, EDX technique and photoluminescence spectroscopy with steady state and time domain measurements. X-ray diffraction and electron diffraction analysis showed that presented synthesis procedure yields pure-phase, well crystallized Lu 2O 3 nanopowders with the particles dimensions in the 30–50 nm range, as observed from TEM images. Luminescence properties of Sm 3+ and Tb 3+ doped Lu 2O 3 exhibited characteristic red and pseudo-white emissions from these rare-earth ions, with an average emission lifetime of 0.8 and 0.6 ms, respectively.

Effects of ZrO 2 addition on phase stability and photocatalytic activity of ZrO 2/TiO 2 nanoparticles

ZrO 2/TiO 2 nanoparticles with various Zr/Ti ratios (0–0.9) were prepared by a polymer complex solution method (PCSM). The prepared samples were characterized using transmission electron microscopy (TEM), the Brunauer, Emmett & Teller (BET) method, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The ZrO 2/TiO 2 photocatalyst showed a high specific area and small crystal size. The XRD pattern for the Zr/Ti = 0.1 sample indicated that the addition of ZrO 2 stabilized the anatase phase of TiO 2 up to 800 °C. The photocatalytic activity of Zr/Ti = 0.1 sample was higher than that of the TiO 2 sample and commercially available Degussa P25. The high photocatalytic activity can be attributed to stronger adsorption in the visible light region, higher specific area, smaller crystal size and increased surface OH groups.

복합고분자용액법에 의한 가시광에 반응하는 TiO2:Zr, N 광촉매의 제조 및 NO 광분해 특성

복합고분자용액법에 의한 가시광에 반응하는 TiO₂:Zr, N 광촉매의 제조 및 NO 광분해 특성

Polymer complex solution synthesis of (YxGd1−x)2O3:Eu3+ nanopowders

Yttrium–gadolinium–europium oxide phosphors are regarded promising for many important optical applications, for example in computed tomography medical imaging and plasma displays. In this work, we investigated procedure for (YxGd1−x)2O3:Eu3+ (x= 0, 0.25, 0.5, 0.75 and 1) nanopowder synthesis using polymer complex solution method (PCS) based on polyethylene glycol fuel (PEG). Structural and emission properties of nanopowders are investigated by X-ray diffraction, electron microscopy and photoluminescence measurements. We obtained particles of about 40nm having excellent structural ordering in cubic bixbyte type of structure – space group Ia3 for all mixed oxide compositions. Luminescence emission measurements exposed characteristic transition of the trivalent europium ion incorporated into insulating host. 5D1 and 5D0 decay time values are measured to obtain information on different kinetic processes occurring for these two emitting levels.

복합고분자 용액법을 이용한 TiO2광촉매 제조 및 특성 평가

Titanium dioxide was prepared by Polymer Complex Solution Method(PCSM) according to the mole ratio of Titanium (IV) isopropoxide(TTIP)/solvent and polymer(Poly Ethylene Glycol). Polymer electrolytes were usually made by dispersing preproduced ceramic nanoparticles in a polymer matrix. Using this method, pure and nano-sized <TEX>$TiO_2$</TEX> powder was synthesized through a simple procedure and polymer entrapment route. At the optimum amount of the polymer, the titanium ions are dispersed in solution and a homogeneous polymeric network is formed. The maximum intensity of anatase phase of <TEX>$TiO_2$</TEX> was achieved by calcining at <TEX>$500^{\circ}C$</TEX> for 2h. The synthesized <TEX>$TiO_2$</TEX> powders were nano-sized and the average size was about 50nm. Anatase/Rutile ratio of the synthesized <TEX>$TiO_2$</TEX> was 70%/30%.

Sintering behaviour of Y 2O 3 powders prepared by the polymer complex solution method

High purity fine Y 2O 3 powder has been prepared by a polymer complex solution method using polyethylene glycol as the complexant of Y 3+ cations. Powder morphology and compacts prepared from three different powder characteristics have been studied. SEM observations were used to know the agglomeration degree of the powders, and the uniformity of powder compacts, and the Hg-porosimetry results to investigate the pore size and microstructure evolution during sintering of the green compacts. The compacts made with the powders calcined at the lower temperatures showed an almost single-peaked pore-size distribution and a more homogeneous microstructure, whereas the pore-size distributions of the compacts made with powders calcined at higher temperatures were double or triple peaked. The sintering behaviour of the low temperature calcined powders exhibited significantly better sinterability and higher densification rate/grain growth rate ratio than the high-temperature calcined powder compacts. Complex rearrangement phenomena relating the pore coordination numbers-grain size-grain morphology appear to occur in the initial and intermediate stages of sintering. In the final stage of sintering, grain growth modified the thermodynamic stability of remaining pores permitting its disappearance although kinetics impeded its complete elimination limiting, thus, the final density to values near theoretical density (≈99.5%).

A polymer complex solution route to the low-temperature synthesis of tetragonal Zr0.88Ce0.12O2 with a reduced amount of organic substance

Abstract Powders of composition Zr0.88Ce0.12O2 were synthesized at reduced temperatures (600–800°C) by a polymer complex solution (PCS) method using polyvinylalcohol (PVA) and by the Pechini-type in situ polymerizable complex (IPC) method. Both methods produced transparent organic polymer complex gels without any precipitation, which after heat treatments at temperatures above 600°C converted to a compositionally homogeneous tetragonal form of Zr0.88Ce0.12O2. It was demonstrated that the PVA-based PCS method overcame a weakness of the IPC method; i.e., the amount of organic substance required for the PVA-based PCS method is less than that required for the IPC method by a factor of about 20.

Synthesis and Characteristics of Complex Multicomponent Oxides Prepared by Polymer Complex Method

Abstract This account focuses on the synthesis and characteristics of ceramics prepared by the Pechini-type in-situ polymerizable complex (IPC) method. The current status of the IPC method is reviewed, and the principle and underlying chemistry of the IPC method is illustrated with a special emphasis on its intrinsic advantage over other solution-based technologies. The method has the ability to prepare complex multicomponent oxides with good homogeneity through mixing at the molecular level. The importance of “polymerization” itself in the IPC route is demonstrated by comparing with the non-polymerizable so-called amorphous citrate method, which affords less compositional homogeneity. The use of heterometallic complexes in the IPC processing is shown to be one of the most promising techniques to synthesize ceramics with exceptionally good homogeneity. It is one function of this account to describe how Raman and 13C NMR spectroscopies can be effectively used for characterizing precursors in the IPC processing. Finally, it is demonstrated that another type of polymer complex solution (PCS) method overcomes the serious drawback of the IPC method; i.e. the amount of organics required for the PCS method is less than that required for the IPC method by a factor of about 20.