Local Structure Modulation Induced Highly Efficient Far-Red Luminescence of La1- xLu xAlO3:Mn4+ for Plant Cultivation.

Modulating the local environment around the emitting ions with component screening to increase the quantum yield and thermal stability is an effective and promising strategy for the design of high-performance fluorescence materials. In this work, smaller Lu3+ was introduced into the La3+ site in a Mn4+-activated LaAlO3 phosphor with the expectation of improving the luminescence properties via lattice contraction induced by cation substitution. Finally, a La1- xLu xAlO3:Mn4+ ( x = 0-0.04) perovskite phosphor with a high quantum yield of 86.0% and satisfactory thermal stability was achieved, and the emission peak at 729 nm well matches with the strongest absorption peak of the Phytochrome PFR. The favorable performances could be attributed to the suppressed cell volume and superior lattice rigidity after the substitution of Lu3+. This work not only obtains a highly efficient La1- xLu xAlO3:Mn4+ ( x = 0.02) phosphor, which holds great potential for application in plant-cultivation light-emitting diodes, but also provides an applicable strategy for further investigation of far-red-emitting phosphors.

Controlling the Electronic Structures of Perovskite Oxynitrides and their Solid Solutions for Photocatalysis.

Band-gap engineering of oxide materials is of great interest for optoelectronics, photovoltaics, and photocatalysis applications. In this study, electronic structures of perovskite oxynitrides, LaTiO2 N and SrNbO2 N, and solid solutions, (SrTiO3 )1-x (LaTiO2 N)x and (SrTiO3 )1-x (SrNbO2 N)x , are investigated using hybrid density functional calculations. Band gaps of LaTiO2 N and SrNbO2 N are much smaller than that of SrTiO3 owing to the formation of a N 2p band, which is higher in energy than the O 2p band. The valence- and conduction-band offsets of SrTiO3 /LaTiO2 N and SrTiO3 /SrNbO2 N are computed, and the adequacy for H2 evolution is analyzed by comparing the positions of the band edges with respect to the standard hydrogen electrode (SHE). The band gap of (SrTiO3 )1-x (LaTiO2 N)x and (SrTiO3 )1-x (SrNbO2 N)x solid solutions are also discussed.

Insights on the relaxation of liposomes encapsulating paramagnetic Ln-based complexes.

PURPOSE: To describe and quantify the different relaxation mechanisms operating in suspensions of liposomes that encapsulate paramagnetic lanthanide(III) complexes. THEORY AND METHODS: The transverse relaxation rate of lanthanide-loaded liposomes receives contribution from the exchange between intraliposomal and bulk water protons, and from magnetic susceptibility effects. Phospholipids vesicles encapsulating different Ln(III)-HPDO3A complexes (Ln = Eu, Gd, or Dy) were prepared using the conventional thin film rehydration method. Relaxation times (T1 , T2 , and T2*) were measured at 14 Tesla (T) and 25 °C. The effect of compartmentalization of the paramagnetic agent inside the liposomal cavity was evaluated by means of an IRON-modified MRI sequence. RESULTS: NMR measurements demonstrated that Curie spin relaxation is the dominant contribution (> 90%) to the observed transverse relaxation rate of paramagnetic liposomes. This was further confirmed by MRI that showed the ability of the liposome entrapped lanthanide complexes to generate IRON-MRI positive contrast in a size dependent manner. CONCLUSION: The Curie spin relaxation mechanism is by far the principal mechanism involved in the T2 shortening of the water protons in suspension of paramagnetic liposomes at 14T. The access to IRON contrast extends the potential of such nanosystems as MRI contrast agents.

Photocatalytic conversion of gaseous ethylbenzene on lanthanum-doped titanium dioxide nanotubes.

The photocatalytic properties of titanium dioxide (TiO2) make it an attractive material for environmental remediation. In the present study, lanthanum (La(3+))-doped TiO2 nanotubes with excellent photocatalytic activity were fabricated by a combination of sol-gel method and hydrothermal technique. The optimal preparation parameters were determined by the structural characterization using a range of methods and the photocatalytic degradation of gaseous ethylbenzene (EB). Compared with pure TiO2 nanoparticles, 1.2%-La(3+)-doped - titania nanotubes (1.2%-La(3+)-TNTs) exhibited higher activity under 254 nm UV for conversion of EB. The initial EB concentrations and relative humidity (RH) obviously influenced the photocatalytic activity of 1.2%-La(3+)-TNTs. Kinetic analysis showed that surface adsorption and surface reaction controlled the rate-determining step for RH of 40-50% and >80%, respectively. Gas chromatography and mass spectrometry were used to analyze the intermediates generated in the conversion of EB, allowing a tentative decomposition pathway to be proposed. The prepared photocatalyst exhibited enhanced EB conversion compared with undoped TiO2, and showed a promise for the decomposition of recalcitrant compounds before subsequent biopurification.

Imagen radiológica de carbonato de lantano / Radiology image of lanthanum carbonate

No disponible

Origin of the low frequency radiation emitted by radiative polaritons excited by infrared radiation in planar La2O3 films.

Upon excitation in thin oxide films by infrared radiation, radiative polaritons are formed with complex angular frequency ω, according to the theory of Kliewer and Fuchs (1966 Phys. Rev. 150 573). We show that radiative polaritons leak radiation with frequency ω(i) to the space surrounding the oxide film. The frequency ω(i) is the imaginary part of ω. The effects of the presence of the radiation leaked out at frequency ω(i) are observed experimentally and numerically in the infrared spectra of La(2)O(3) films on silicon upon excitation by infrared radiation of the 0TH type radiative polariton. The frequency ω(i) is found in the microwave to far infrared region, and depends on the oxide film chemistry and thickness. The presented results might aid in the interpretation of fine structures in infrared and, possibly, optical spectra, and suggest the study of other similar potential sources of electromagnetic radiation in different physical scenarios.

Sonocatalytic degradation of amaranth catalyzed by La3+ doped TiO2 under ultrasonic irradiation.

The relationship between the physicochemical properties and the activity of sonocatalysts is investigated and elucidated in the sonodegradation of amaranth. The sonocatalyts are composed of La(3+) doped TiO(2) synthesized via a sol-gel process. The sonocatalysts are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopic analysis, UV-Vis absorption spectroscopy, and X-ray photoelectron emission spectroscopy. The sonodegradation products of amaranth are analyzed by UV-Vis absorption spectroscopy. The presence of the La(3+) doped TiO(2) catalysts substantially enhances the sonocatalytic degradation of amaranth in aqueous suspensions. The possible sonocatalytic mechanisms for such are discussed.

Photocatalytic degradation of commercial methyl parathion in aqueous suspension containing La-doped TiO2 nanoparticles.

The photocatalytic degradation of a commercial methyl parathion (MP) under UV irradiation was investigated in aqueous suspension containing lanthanum-doped mesoporous TiO2 nanoparticles (La/m-TiO2) as photocatalyst. The rate of photodecomposition of MP was measured using UV-Vis spectrophotometry, and its mineralization was followed using ion chromatography (IC). The identification of possible intermediate products was carried out using several powerful analytical techniques such as gas chromatography-pulsed flame photometric detector (GC-PFPD) and high performance liquid chromatography-mass spectroscopy (HPLC-MS). Under our conditions, complete disappearance of 20 mg/L of MP occurred within 2 h of illumination, whereas complete mineralization of MP was not achieved through IC analysis. There was a single intermediate product found in the research, which was identified to be methyl paraoxon, owing to the substitution of S by the O atom in the MP molecule. Based on the experimental facts, it is concluded that MP was mainly attacked not by OH radicals but photo-generated holes (h+), resulting from the good adsorption of MP on the catalyst surfaces due to the enhanced adsorption by La doping.

LaBr(3):Ce and SiPMs for time-of-flight PET: achieving 100 ps coincidence resolving time.

The use of time-of-flight (TOF) information in positron emission tomography (PET) enables significant improvement in image noise properties and, therefore, lesion detection. Silicon photomultipliers (SiPMs) are solid-state photosensors that have several advantages over photomultiplier tubes (PMTs). SiPMs are small, essentially transparent to 511 keV gamma rays and insensitive to magnetic fields. This enables novel detector designs aimed at e.g. compactness, high resolution, depth-of-interaction (DOI) correction and MRI compatibility. The goal of the present work is to study the timing performance of SiPMs in combination with LaBr(3):Ce(5%), a relatively new scintillator with promising characteristics for TOF-PET. Measurements were performed with two, bare, 3 mm x 3 mm x 5 mm LaBr(3):Ce(5%) crystals, each coupled to a 3 mm x 3 mm SiPM. Using a (22)Na point source placed at various positions in between the two detectors, a coincidence resolving time (CRT) of approximately 100 ps FWHM for 511 keV annihilation photon pairs was achieved, corresponding to a TOF positioning resolution of approximately 15 mm FWHM. At the same time, pulse height spectra with well-resolved full-energy peaks were obtained. To our knowledge this is the best CRT reported for SiPM-based scintillation detectors to date. It is concluded that SiPM-based scintillation detectors can provide timing resolutions at least as good as detectors based on PMTs.

Synthesis and characterization of La2O3/TiO2-xFx and the visible light photocatalytic oxidation of 4-chlorophenol.

In this work, we investigated the synergetic effect of La and F on the visible light photocatalytic activity of TiO(2) catalysts. La(2)O(3)/TiO(2-x)F(x) photocatalysts were prepared by a simple sol-gel process using tetrabutyl titanate (TBT), La(NO(3))(3) and NH(4)F as precursors. XPS results revealed that La(2)O(3) accumulated on the surface of TiO(2), which enhanced the surface area of TiO(2) and inhibited the recombination of electron-hole pairs. It also showed that two kinds of fluorine species were formed and these increased the acid active sites and enhanced the oxidation potential of the photogenerated holes in the valance band. UV-vis diffuse reflection spectra of La(2)O(3)/TiO(2-x)F(x) showed that intraband gap states were present and these are probably responsible for its absorption of visible light while the intrinsic absorption band was shifted slightly to a longer wavelength. At molar ratios of La and F to Ti of 1.5:100 and 5:100 and after calcination at 500 degrees C, the degradation rate of 4-chlorophenol (4-CP) over the sample was about 1.2-3.0 times higher than that of the other doped samples and undoped TiO(2). The total organic carbon (TOC) removal rates of 4-CP showed that 4-CP was mineralized efficiently in the presence of the sample under visible light illumination.

Investigation of the PGNAA using the LaBr3 scintillation detector.

The Joint Research Centre of the European Commission develops instrumentation for detection of hazardous materials. In relation to this a new experimental facility was constructed for research into methods applying the detection of characteristic gamma rays subsequent to neutron irradiation. This includes the detection of prompt gamma rays from neutron inelastic scattering and neutron capture. For this purpose the device employs LaBr(3) scintillation detectors. The paper investigates the applicability of the LaBr(3) scintillation detector to PGNAA.

Facile fabrication of pomponlike microarchitectures of lanthanum molybdate via an ultrasound route.

Pomponlike La(2)(MoO(4))(3) microstructures assembled with single-crystalline nanoflakes have been facilely fabricated via a surfactant-assisted ultrasound route for the first time. Various synthesis conditions were examined, such as the surfactant concentration, the molecular structure of surfactants, and the pH value. The obtained pomponlike microstructures were characterized by X-ray diffraction (XRD), (field-emission) scanning electron microscopy [(FE)SEM], transmission electron microscopy (TEM), and nitrogen adsorption/desorption isotherms. It has been revealed that a minimum concentration of sodium dodecylsulfate (SDS) was required for the formation of pomponlike La(2)(MoO(4))(3) microstructures. When the SDS concentration is above 0.02 mol L(-1), the pomponlike microstructures become more perfect, and the size is also increased with the increasing SDS concentration. Under the same sonication, similar pomponlike microstructures were obtained when a cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used instead of the anionic surfactant SDS, indicating that the hydrophobic alkyl chains are an important factor for the formation of the pomponlike La(2)(MoO(4))(3) microstructures. It is also found that the pomponlike La(2)(MoO(4))(3) microstructures can only be obtained within an optimal pH range of 8.0-9.0 under sonication. Based on TEM, Fourier transform infrared spectroscopy (FT-IR) and solubilization experiment, a formation mechanism of pomponlike La(2)(MoO(4))(3) microstructures was proposed, in which the collaborative action of surfactants and sonication plays a key role. Furthermore, the porosity of the pomponlike La(2)(MoO(4))(3) microstructures were discussed.

Directionally controlled 3D ferroelectric single crystal growth in LaBGeO5 glass by femtosecond laser irradiation.

Laser-fabrication of complex, highly oriented three-dimensional ferroelectric single crystal architecture with straight lines and bends is demonstrated in lanthanum borogermanate model glass using a high repetition rate femtosecond laser. Scanning micro-Raman microscopy shows that the c-axis of the ferroelectric crystal is aligned with the writing direction even after bending. A gradual rather than an abrupt transition is observed for the changing lattice orientation through bends up to approximately 14 degrees. Thus the single crystal character of the line is preserved along the bend through lattice straining rather than formation of a grain boundary.

Correlation between the band positions of (SrTiO3)1-x.(LaTiO2N)x solid solutions and photocatalytic properties under visible light irradiation.

N-doped SrTiO3 and (SrTiO3)1-x.(LaTiO2N)x samples were prepared by the thermal ammonolysis method. The photocatalytic activities of the samples were investigated in a water suspension system. Aqueous methanol solution (50 mL CH3OH + 220 mL H2O) for H2 evolution and aqueous silver nitrate solution (270 mL, 0.01 mol L(-1)) for O2 evolution were used as sacrificial reagents. The oxynitrides showed photocatalytic activities under visible light irradiation. The maximum rates of photocatalytic hydrogen and oxygen evolution under visible light irradiation (lambda > 420 nm) were 10 and 8 micromol h(-1), respectively. The samples were characterized by X-ray diffractometry, UV-Vis spectrophotometry, Fourier transform infrared spectrometry, and laser Raman spectroscopy. The unit cell edge length of (SrTiO3)1-x.(LaTiO2N)x increased linearly and their band gaps reduced from 3.18 to 2.04 eV with increasing x from 0 to 0.30. Moreover, the calculation results of (SrTiO3)0.75.(LaTiO2N)0.25 by density functional theory suggested that the band gap narrowing of the solid solutions came from the hybridization of N2p and O2p orbital. The band positions of the solid solutions were further investigated by Mott-Schottky and the onset potential method. The results suggested that the conduction band of the solid solution was lowered, which led to decrement of the hydrogen evolution rate.

Decay time characteristics of La2O2S:Eu and La2O2S:Tb for use within an optical sensor for human skin temperature measurement.

We focus on the development of a remote temperature sensing technology, i.e., an optical laser-based sensor, using thermographic phosphors for medical applications, particularly within an electromagnetically hostile magnetic resonance imaging (MRI) environment. A MRI scanner uses a strong magnetic field and radio waves to generate images of the inside of the body. The quality of the image improves with increasing magnetic resonance; however, the drawback of applying a greater magnetic strength is the inducement of heat into the body tissue. Therefore, monitoring the patient's temperature inside MRI is vital, but until now, a practical solution for temperature measurement did not exist. We show europium doped lanthanum oxysulphide (La(2)O(2)S:Eu) and terbium doped lanthanum oxysulphide (La(2)O(2)S:Tb) are both temperature sensitive to a low temperature range of 10-50 degrees C when under ultraviolet (UV) excitation. The emission spectra and decay time characteristics of these phosphors were demonstrated. The results indicate that La(2)O(2)S:Eu has a quenching rate of 13.7 m degrees C(-1) and 4 m degrees C(-1) at 512 nm and 538 nm, respectively. In addition, La(2)O(2)S:Tb has a lower quenching rate of 4.19 m degrees C(-1) at 548 nm due to its faster decay time.

Applications of a polymeric microgel template/ultrasonic degradation method: preparation of poly(sodium acrylate)/La(OH)3 nano-composites.

A polymeric microgel template/ultrasonic degradation method for the preparation of organic-inorganic nano-composites is proposed and successfully used in the preparation of poly(sodium acrylate) (PAANa) and lanthanium hydroxide nano-composites (PAANa/La(OH)(3)). The nano-composites were prepared via three steps. La(NO(3))(3) was trapped within the PAANa microgels first, and then the metal ions within the microgels were hydrolyzed by slow introduction of ammonia. Finally, the composites of the micro-particles were degraded by ultrasonic treatment. The product was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The average diameter of the composites prepared in this way is about 50 nm and the size distribution of them is narrow. TGA analysis shows that the content of La(OH)(3) in the composites is about 20%.

Kinetic study of the thermoluminescence of KMgF3:LaF3 compounds employing the general one trap model.

The parameters characterising the trap centres involved in the thermoluminescence of KMgF3:LaF3 compounds have been found by deconvolving the glow curve with the General One Trap model (GOT). For the fitting procedure the Levenberg-Marquardt method has been employed. Tm-T(stop) measurements along with initial rise measurements were performed in order to estimate the number of peaks the glow curve is made up of, and the corresponding activation energies. Instead of the Runge-Kutta method, a novel algorithm has been employed to integrate the differential equation of the GOT model, which reduces the computational time nearly 30 times with respect to the former when the glow curve is recorded with a lineal heating rate profile. The strong computational time reduction makes feasible a large number of runs with different guess values. An interesting result is that the concentration of disconnected deep traps is much less than the concentration of trap centres.

Polyol-mediated synthesis and photoluminescent properties of Ce3+ and/or Tb3+-doped LaPO4 nanoparticles.

Rare-earth ion (Ce3+, Tb3+) doped LaPO4 nanoparticles were prepared by the polyol method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and lifetimes. The results of XRD indicate that the as-prepared nanoparticles are well-crystallized at 160 degrees C and assigned to the monoclinic monazite structure of the LaPO4 phase. The obtained LaPO4:Ce3+, Tb3+ nanoparticles are spherical with narrow size distribution and average size of 20 nm. The doped rare-earth ions show their characteristic emission in LaPO4 nanoparticles, i.e., Ce3+ 5d-4f and Tb3+ 5D4-7FJ (J = 6-3) transitions, respectively. The optimum doping concentration for Tb3+ in La(0.8-x)Ce0.2TbxPO4 nanoparticles is determined to be 15 mol% (x = 0.15). The luminescence decay curves of Ce3+ in LaPO4:Ce3+ and LaPO4:Ce3+, Tb3+ nanoparticles present a single-exponential behavior, and the lifetimes (tau) of Ce3+ decrease with increasing Tb3+ concentrations (at the constant Ce3+ concentration) in LaPO4:Ce3+, Tb3+ nanoparticles due to the energy transfer from Ce3+ to Tb3+. The energy-transfer efficiency from Ce3+ to Tb3+ was calculated, which depends on the doping concentrations of Tb3+ if the concentration of Ce3+ is fixed.

Observations on the background spectra of four LaCl 3 Ce scintillation detectors.

Our laboratory has purchased four LaCl (3)(Ce) scintillation crystals over the course of the last year for evaluation as part of an environmental management research and development project. In addition to the expected content of naturally radioactive (138)La, we have found that all four of these detectors are contaminated to various degrees with alpha particle emitting nuclides that we have determined to be (227)Ac and its daughters. The impact of these radionuclides on the background spectra and, thus, on the detection sensitivity of these detectors is presented and discussed.