Ce Powder Research Articles

Ultrasound assisted synthesis of Gd and Nd doped ceria electrolyte for solid oxide fuel cells

Abstract In this study, the ceramic powders of Ce 1− x Gd x O 2− x /2 and Ce 1− x Nd x O 2− x /2 ( x =0.05, 0.10, 0.15, 0.20 and 0.25) were synthesized by ultrasound assisted co-precipitation method. The ionic conductivity was studied as a function of dopant concentration over the temperature range of 300–800 °C in air, using the impedance spectroscopy. The maximum ionic conductivity, σ 800 °C =4.01×10 −2 Scm −1 with the activation energy, E a =0.828 kJmol −1 and σ 800 °C =3.80×10 −2 Scm −1 with the activation energy, E a =0.838 kJmol −1 were obtained for Ce 0.90 Gd 0.10 O 1.95 and Ce 0.85 Nd 0.15 O 1.925 electrolytes, respectively. The average grain size was found to be in the range of 0.3–0.6 μm for gadolinium doped ceria and 0.2–0.4 μm for neodymium doped ceria. The uniformly fine crystallite sizes (average 12–13 nm) of the ultrasound assisted prepared powders enabled sintering of the samples into highly dense (over 95%) ceramic pellets at 1200 °C (5 °C min −1 ) for 6 h.

Luminescence properties and decay kinetics of nano ZnO powder doped with cerium ions

ZnO nanopowders doped with cerium ions (1.2 and 1.5 at. wt.%) were synthesized through soft solution route using ultrasound. Sonication has been found to be an effective way for doping rare earth ions like cerium into ZnO. This was confirmed from energy dispersive analysis of X-rays (EDAX) measurement. Further, optical absorption and photoluminescence (PL) measurements corroborate this finding. X-ray diffraction (XRD) studies show the increase of crystallite size and unit cell volume with doping of cerium ions. Formation of fibrous structure of ZnO:Ce was observed from the transmission electron microscopy (TEM) measurements. Although the structural measurements indicate Ce4+ ion occupying substitutional site in ZnO, PL and absorption studies confirmed the presence of Ce3+ ion in the powder. The coexistence of Ce3+ and Ce4+ ions has been explained on the basis of conversion of Ce3+ to Ce4+ in the oxidizing environment. Thermoluminescence (TL) and photo-stimulated decay of luminescence (PSDL) decay studies give an idea of various trapping levels present in the band gap of ZnO. These traps release electrons during optical stimulation to give bimolecular kinetics in nano ZnO:Ce powders.

Granulation of Fe–Al–Ce trimetal hydroxide as a fluoride adsorbent using the extrusion method

Iron–aluminum–cerium hydroxide (Fe–Al–Ce), which has high fluoride (F) adsorption capacity, was granulated via extrusion with cross-linked poly (vinyl alcohol) (PVA) as the binder. The optimum granulation conditions for acquiring an adsorbent with a high F adsorption capacity and compression strength were: binder/Fe–Al–Ce powder ratio, 1.4; average cylinder diameter of granules, 1.6mm; and drying temperature, 65°C. The granulated Fe–Al–Ce (GFAC) exhibited a Langmuir maximum adsorption capacity of 51.3mgg−1 at pH 7.0±0.2. The GFAC in columns exhibited an accumulated F adsorption capacity of 5.7mgg−1 and 3.2mgg−1 at the breakthrough point (1.0mgFl−1) for treatment of F-spiked tap water (pH 7.8±0.2) and F-bearing groundwater (pH 8.2±0.2), respectively, which is several times higher than most reported F adsorbents under the same conditions. Energy dispersive X-ray micro analysis (EDX) showed that F was distributed evenly in the cross-section of the used GAFC, suggesting that most active sites inside the GFAC were available for F removal. A regeneration method using NaAlO2 solution to desorb F from the used GFAC was developed, permitting the GFAC to keep over 60% of its F adsorption capacity even after four adsorption–regeneration cycles. The results demonstrated that GFAC was superior in F adsorption performance to conventional adsorbents such as activated alumina.

Dependence of Crystal Structures and Scintillation Properties on Cerium Concentration in Gd2Si2O7:Ce Powder Synthesized by Solid State Reaction

Dependence of Crystal Structures and Scintillation Properties on Cerium Concentration in Gd2Si2O7:Ce Powder Synthesized by Solid State Reaction

Novel Solution Synthesis of White LED Phosphors by Microreaction Method

A rare earth ion activated phosphor material has been successfully synthesized for the first time using a newly developed microreaction system. Control of the particle size of Y3Al5O12:Ce3+ (YAG:Ce) yellow phosphor powder has been attempted by changing the reaction space. The size can be varied between 400-1000 nm by maintaining almost the same photoluminescent performance. An internal quantum efficiency of 85% has been achieved for the YAG:Ce powder sample having an average particle size of 400 nm.

Study on the cerium oxidation state in a Lu0.8Sc0.2BO3 host

Lu0.8Sc0.2BO3:Ce powders doped with different forms of cerium [CeF3, CeO2 or Ce(NO3)3] were synthesized by solid-state methods under different conditions (carbon powders, nitrogen or air) and studied by a combination of X-ray excited luminescence spectra, optical diffuse reflectance spectra, fluorescence decay curves and X-ray absorption near edge spectroscopy. The optical diffuse reflectance spectra and fluorescence decay curves confirmed the different Ce3+/Ce4+ ratios in the samples of interest. Based on the Ce LIII-edge XANES spectra, we finally concluded that the differences in the scintillation intensities of the samples of interest originate from the varied Ce3+/Ce4+ ratios, which explains why the sample doped with CeF3 and synthesized under carbon powder conditions shows an optimal scintillation emission. The specific Ce3+/Ce4+ ratio was also qualitatively determined by fitting the Ce LIII-edge XANES spectra. More importantly, this study further demonstrates the effectiveness of using XANES spectroscopy to investigate the cerium oxidation state in cerium-doped scintillators.

Mn–Ce oxide as a high-capacity adsorbent for fluoride removal from water

A novel Mn–Ce oxide adsorbent with high sorption capacity for fluoride was prepared via co-precipitation method in this study, and the granular adsorbent was successfully prepared by calcining the mixture of the Mn–Ce powder and pseudo-boehmite. High-resolution transmission electron microscopy (TEM) image showed that the Mn–Ce adsorbent consisted of about 4.5nm crystals, and X-ray diffraction (XRD) analysis indicated the formation of solid solution by Mn species entering CeO2 lattices. The surface hydroxyl group density on the Mn–Ce adsorbent was determined to be as high as 15.3mmolg−1, mainly responsible for its high sorption capacity for fluoride. Sorption isotherms showed that the sorption capacities of fluoride on the powdered and granular adsorbent were 79.5 and 45.5mgg−1 respectively at the equilibrium fluoride concentration of 1mgL−1, much higher than all reported adsorbents. Additionally, the adsorption was fast within the initial 1h. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that the hydroxyl groups on the adsorbent surface were involved in the sorption of fluoride. Both anion exchange and electrostatic interaction were involved in the sorption of fluoride on the Mn–Ce oxide adsorbent.

Optically stimulated luminescence (OSL) of Lu 2SiO 5:Ce powder: A preliminary study

Optically stimulated luminescence (OSL) of Lu 2SiO 5:Ce powder (Phosphor Technology Ltd., UK) has been measured by Risø TL/OSL Reader (TL-DA-15). Upon blue photon stimulation ( λ ex ∼470 nm) the material shows strong OSL signal that can detect β-irradiation right up to the dose of ∼0.2 Gy. A brief discussion on this finding is presented by comparing the thermoluminescence of the system with and without optical stimulation. The two key important parameters namely, trap-depth ( E) and frequency factor ( s) of the main peaks that occur at 85 and 232 °C are determined.

Synthesis of Pb 1− xR xZr 0.65Ti 0.35O 3 ( x = 0.05, 0.10 and 0.15; R = Ce, Pr and Nd) powders by Gel Entrapment Technique and study on their thermo-physical and electrical properties

Rare earth doped lead zirconate titanate of composition (Pb 1− x R x Zr 0.65Ti 0.35)O 3 where x = 0, 0.10 and 0.15 and R = Ce, Pr and Nd was prepared by Gel Entrapment Technique (GET). The gel was suitably calcined at 1073 K and the resultant product was characterized by XRD, SEM, BET surface area analysis and Dynamic Light Scattering. The dielectric constants of PZT were found to decrease with Ce doping where as it increased with Pr doping. The pyrochlore phase in Nd doped samples was found to be responsible for lower conductivity and dielectric constant values. The redox behaviour of the compounds was studied by TPR–TPO measurements.

Luminescence characteristics of YAP:Ce scintillator powders and composites

Cerium doped yttrium aluminate perovskite YAlO 3 (YAP) powders are pursued as interesting alternatives to bulk crystals for application in scintillating devices. The emissions of these materials in the near-UV and visible spectral regions originate from electric dipole transitions between 4f and 5d energy levels of Ce 3+ and largely depend on the environment occupied by the ion. In search for improved synthesis conditions that can lead to phase pure powders with optimized structural and spectroscopic characteristics, in this work we have employed the polymeric precursor (Pechini) method to prepare crystalline and amorphous YAP:Ce powders doped with 1–10 mol% Ce 3+. Interesting composite materials were also obtained by dispersing some of the YAP:Ce powders in silica xerogels. A comparative structural and spectroscopic study of all the samples was done by XRD, FT–IR, emission, excitation and excited state lifetime measurements. In agreement with previous reports, excitation at 296 nm results in intense emission in the range 315–425 nm with an average decay time of 30 ns.

Evaluation of the Luminescence Efficiency of YAG:Ce Powder Scintillating Screens for Use in Digital Mammography Detectors

In the present study scintillating screens prepared from Y3Al5O12:Ce (YAG:Ce) powder phosphor were evaluated for use in digital mammography. YAG:Ce has never previously been used in X-ray medical imaging, however since it emits green light (i.e peak at 550 nm), it is expected to match well the spectral sensitivities of most photodetectors (photodiodes, CCDs and amorphous silicon sensors) incorporated in various digital mammography detectors. YAG:Ce was purchased in powder form and was used in order to prepare test screens in the laboratory. Screens were evaluated by determining the quantum detection efficiency (QDE), the energy absorption efficiency (EAE), the absolute luminescence efficiency, the X-ray luminescence efficiency (XLE), the light emission spectrum, the X-ray to light intrinsic conversion efficiency and the spectral compatibility with various photodetectors. Results were compared with phosphor materials commercially employed in X-ray imaging such as CsI:Tl and Gd2O2 S:Tb. Maximum YAG:Ce emission efficiency was observed for the 63 mg/cm2 screen at 49 kVp. The spectral compatibility with amorphous silicon photodiodes (0.93) and CCDs (0.95) was found to be very high, better than the corresponding compatibility of the CsI:Tl screen, mostly used in current digital radiography detectors. Taking into account the YAG:Ce overall performance, its short decay time as well as its spectral compatibility with amorphous silicon detectors and CCDs, YAG:Ce could be of interest for further investigation for applications in digital mammography.

Electrochemical oxidation of Ce(III) to Ce(IV) and deposition of copper powder in an electrolytic membrane reactor

The electrolytic oxidation of Ce(III) to Ce(IV) at the anode and the simultaneous deposition of copper powder at the cathode were investigated in an electrolytic membrane reactor in sulfuric acid media. The performance of the electrolytic reactor for the oxidation of Ce(III) and copper powder production was optimized by studying the effects of current density, copper(II) and acid concentrations in the catholyte; and various combinations of current density on current efficiency and cell voltage. Experimental results show that copper deposition at the cathode improves the anode current efficiency for the oxidation of Ce(III). Under the optimized conditions, a maximum Ce(III) conversion ratio of 99% was achieved with a current efficiency of 80%. In addition, ∼ 95% Cu was deposited in the form of powder with a current efficiency of 91%. The oxidation of Ce(III) and simultaneous deposition of copper powder can reduce the cell voltage and increase anodic current efficiency.

Gamma Ray Scintillators via BaF2:Ce Nanopowders

Nano-scale BaF2:Ce phosphor powders (“nanophosphors”) show great potential for improving the functioning of inorganic scintillators for gamma ray detectors. These particles may offer greater ef ciency and ease of manufacture than most state-of-the-art single crystal scintillators currently in use. Chemical precipitation similar to that of LaF3: Ce synthesis was used to prepare the BaF2:Ce powders, while care was taken to optimize doping levels to prevent internal absorption while maximizing photon production. Select particle samples were then encapsulated in a polymer matrix in an attempt to improve mechanical robustness while maintaining photon yield. Results from photoluminescence excitation and emission measurements of samples of BaF2: Ce powders doped from 1-30mol% suggest that the BaF2:15mol%Ce sample exhibited the greatest photon production, but that a more UV transparent polymer must be found in order to maximize light transmission when the powder is encapsulated in a polymer matrix.

Synthesis of LnCuS<SUB>2</SUB> (Ln=Ce, Pr, Nd, Sm, Gd, and Tb) Powder by Polymerized Complex Method and CS<SUB>2</SUB> Gas Sulfurization

Rare earth copper sulfides, 2 (Ln = Ce, Pr, Nd, Sm, Gd and Tb), powders were synthesized by the following procedure: (1) complex oxide was synthesized using the polymerized complex method, and (2) LnCuO 2 was sulfurized by the CS 2 gas. CS 2 gas sulfurization combined with a polymerized complex method can reduce a reaction temperature and a duration time. TG-DTA and XRD results indicated that Ln'-Cu polymerized complex (Ln = Pr, Nd, Sm and Gd) was decomposed into Ln'203 (via Ln' 2 OCO 3 ) and Cu/CuO. Ln' 2 0 3 reacted with CuO to form Ln' 2 CuO 4 complex oxide. In the case of Ce and Tb (Ln), a Ln-Cu polymerized complex was decomposed into (LnO 2 and Cu/CuO. Ln 2 CuO 4 phase was not observed in these cases. In sulfurization reaction, XRD indicates that Ln'CuS 2 was formed via a formation of Ln'OCuS. On the other hand, LnCuS 2 is considered to be formed via a solid state reaction between Ln 2 S 3 and Cu 2 S. The contents of oxygen and carbon impurities in the products depend on the sulfurization reaction conditions. For example, the PrCuS 2 powder was obtained with low impurity contents of 0.07 mass% C and 0.073 mass% O by sulfurization at 1223 K.

Hydrothermal synthesis of Ce: Lu 2SiO 5 scintillator powders

The synthesis of cerium-doped lutetium oxyorthosilicate (LSO) polycrystalline powders was investigated by a hydrothermal process. The precursor was obtained by the hydrothermal reaction of Lu(NO 3) 3 with Na 2SiO 3 at 200 °C for 10 h by using urea as precipitator, followed by a calcination under proper temperatures. The results of XRD indicated that the precursor was crystallized into A-type LSO phase at 1000 °C, and transferred to B-type LSO phase when temperature was raised above 1050 °C. After being heated at 1250 °C for 2 h, single phase of B-type LSO powder was synthesized with homogeneous distribution of particle size ranging from 200 to 300 nm. The photoluminescence spectrum of as-synthesized LSO: Ce powders showed a typical broad emission peak centered at 404 nm, corresponding to the 5d 1–4f transition of Ce 3+.

Imaging performance and light emission efficiency of Lu2 SiO5:Ce (LSO:Ce) powder scintillator under X-ray mammographic conditions

The aim of the present study was to measure the imaging transfer characteristics and the luminescence efficiency (XLE) of a Lu2SiO5:Ce (LSO:Ce) powder scintillator for use in X-ray mammography detectors. An LSO:Ce powder scintillating screen, with a coating thickness of 25 mg/cm2, was prepared in our laboratory. The imaging performance of the screen was assessed by experimental determination of the modulation transfer function (MTF) and the detective quantum efficiency (DQE) as well as single index image quality parameters such as noise equivalent pass band (Ne) and informational efficiency (n I). A theoretical model, describing radiation and light transfer, was fitted to experimental MTF values in order to estimate optical properties of the scintillator. Screen irradiation was performed under exposure conditions employed in mammographic applications (27 kVp, 63 mAs). MTF was determined by the square wave response function (SWRF) method. Results showed that LSO:Ce exhibits high MTF and DQE values, which are comparable to those of the commercially used Gd2O2S:Tb. Considering our image quality parameters and luminescence efficiency results as well as the fast response of the LSO:Ce scintillator screen (40 ns), this material can be considered for use in X-ray mammographic detectors.

Co-precipitation Synthesis and Photoluminescence of YAG:Ce Phosphors

Ce-doped YAG (Y3−x Al5O12:xCe, YAG:Ce) phosphor were prepared by co-precipitation method using ammonium hydrogen carbonate as a precipitant. The influence of precipitation condition such as pH on the powder properties and the optimum Ce content in YAG:Ce were investigated. Throughout the experiment, phase pure YAG:Ce powders with 50 ∼ 70 nm particle sizes were obtained. The luminescence intensity and particle size increased as calcination temperature increased in the range of 900 ∼ 1300°C. The maximum luminescent intensity was observed at 2 mol % of Ce concentration in the YAG:Ce phosphor. The luminescent intensity the YAG:Ce particles was significantly affected by the pH of the precipitation condition. Within the scope of this study (pH 5–8), the lower pH was favored for the higher emission intensity. The phosphors prepared had maximum excitation band at 467 nm and a maximum emission band at 525 ∼ 530 nm.

Synthesis Study of Lu<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB>(Ce) Nanoscaled Powder by Co-precipitation

Ce3+-doped Lutetium aluminum garnet Lu3Al5O12 phosphors were prepared by an anti co-precipitation from mixing solution of lutetium,aluminum and cerium nitrates using the ammonium hydrogen carbonate as precipitate,followed by the calcination at low temperatures.TG-DTA,FTIR,XRD,TEM and Photoluminescence were used to characterize the as-prepared phosphors.The calcining temperature has distinctly influence on the particle size and the photoluminescence of the prepared Lu3Al5O12(Ce) powders.The resulted Lu3Al5O12(Ce) powder calcined at 1000℃ for 2h has an average particle size of 30nm.And its photoluminescence is the strongest among the powders calcined in the range from 850℃ to 1200℃.

Oxygen Nonstoichiometry and Defect Chemistry Modelling of Ce0.8PrxTb0.2-xO2-δ

Powders of Ce_{0.8}Pr_{x}Tb_{0.2-x}O_{2-δ} solid solutions (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized by co-precipitation. After sintering at 1500^{o}C in Air for 12h and subsequent annealing in either reducing or oxidizing conditions, the powders were observed by XRD to be single phase fluorites. The oxygen nonstoichiometry was determined over a wide PO2 range at 600/700/800/900^{o}C by coulometric titration and validated for the x = 0.20 composition by thermogravimetry. XANES measurements were performed at the Ce/Pr/Tb L3 and L2 edges. The valence state of each dopant was found to be affected by the presence of the co-dopant. The total 4-valent dopant fraction obtained from XANES, matches well the one determined by coulometric titration. A defect model was developed that accounts well for the determined oxygen nonstoichiometry Ce_{0.8}Pr_{x}Tb_{0.2-x}O_{2-δ} over the entire P_{O2} range.

Investigation of Luminescence Properties of Lu$_{2}$SiO$_{5}$:Ce (LSO) Powder Scintillator in the X-Ray Radiography Energy Range

This paper investigates the light emission efficiency of Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> :Ce (LSO) powder scintillator under conditions employed in projection X-ray imaging. Although single-crystal LSO has been thoroughly studied in medical imaging energies, the efficiency of powder LSO has not been previously investigated experimentally under X-ray medical radiography conditions. For this purpose, three scintillating screens with a coating thickness of 63.4, 108.4, and 172.5 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were prepared by sedimentation of LSO powder. Measurements of luminescence efficiency (emitted light energy flux over incident X-ray energy flux) were performed in the radiographic X-ray tube voltages range (40-140 kVp). Parameters related to X-ray detection, i.e., quantum detection efficiency, energy absorption efficiency and probability of K-fluorescence reabsorption were calculated. A theoretical model, describing radiation and light transfer, was employed to fit luminescence experimental data and to estimate values of the intrinsic conversion efficiency and of the light attenuation coefficients of the scintillating screens. The spectral compatibility of the LSO powder scintillator to various optical detectors used in digital radiography was also determined by performing light emission spectrum measurements and by taking into account the spectral sensitivity of electronic optical detectors. Maximum values of LSO luminescence efficiency were observed within the range from 40 to 60 kVp. The 172.5 mg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> thick screen was found more efficient than the two thinner screens examined in our experiments. The intrinsic conversion efficiency of LSO (0.10) was found close to that of currently employed phosphors. Spectral compatibility data of LSO screens indicates that LSO may be efficiently coupled to optical detectors used in digital radiography imaging systems.