To improve its light conversion efficiency, NaYF4:(Yb3+, Er3+) upconversion (UC) phosphor, which generates one visible photon by absorbing two or more near-infrared photons, was coated with SiO2 nanoparticles. The surface modification of phosphor was performed by using a modified sol–gel method as a function of the concentration of colloidal silica employed as the surface coating precursor. It was found that the PL intensities depend on the concentration of colloidal silica. When a 2.7 wt% concentration of colloidal silica was used, the NaYF4:(Yb3+, Er3+) phosphor exhibited a homogeneous coating with silica and an approximately 9% increase in the PL intensity, as compared with that of the non-coated sample of NaYF4:(Yb3+, Er3+) phosphor. This increase in the PL intensity can be explained by the suppression of the nonradiative recombination of electron–hole pairs via surface defects. The experimental results suggest that the surface modification of upconversion phosphors with a silica coating of the appropriate concentration is a simple and effective solution to improve the light conversion efficiency of upconversion phosphors used in optoelectronic devices.

We have developed a real-time dose monitoring system for a low-energy ion-beam facility. Before we developed the monitoring system, the system had given a substantial error of ±23% when we irradiated an ion beam with a dose as much as 3.0 × 1016 cm−2 on the Si substrate. Moreover, a low irradiation dose as small as 1013 cm−2 was scarcely able to be controlled because of a too short irradiation time of several seconds, producing a greater dose error. To develop a real-time dose monitoring system, in this work, we employed a current integrator in conjunction with a beam stopper, by which a dose of 3.0 ×1016 cm−2 can be exactly irradiated on the sample with less than ±6% error, which was ensured by the measurements of Rutherford backscattering spectroscopy.

To date, it is unknown whether the combination of Dy ions and superparamagnetic iron oxide (SPIO: Fe3O4) NPs can offer improved performance in UHF-MRI. In this work, we provide a paradigm of hierarchical surface-structured (His) DyxFe3-xO4 NPs as T-2 MRI nanoprobes at UHF (9.4T). We found that His-DyxFe3-xO4 NPs (x = 0.2) possess a higher transverse relaxivity than unmodified His-SPIO NPs and a significantly enhanced r(2)/r(1) ratio (up to10.4 times higher) than those of reported Dy-based T-2 MRI probes at 9.4 T. Furthermore, we demonstrate the effects of surface design of DyxFe3-xO4 NPs on their magnetic relaxivity and in vivo performance at UHF. The markedly enhanced r(2)/r(1) of His-DyxFe3-xO4 NPs (x = 0.2) at 9.4 T is mainly attributed to decreased r(1) relaxivity owing to the surface design and the possible disturbance of the Dy-Fe superexchange interaction. This work could provide an insightful strategy for the design of lanthanide-doped magnetic nanosystems as potential T-2 MRI nanoprobes in UHF. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

To improve the light conversion efficiency of the upconversion phosphor NaYF₄:Yb3+, Tm3+ for use in solar cells, its phosphor surface was treated by removing the NaF phase from the surface of the NaYF₄ host crystals. The surface of the phosphor was treated by a simple procedure consisting of washing, filtering, and drying. It is confirmed that the NaF compound is efficiently eliminated from the surface of NaYF₄-based phosphors by this surface treatment. The experimental results strongly suggest that the removal of NaF from the surface of the NaYF₄:Yb3+, Tm3+ phosphor reduces surface defects and enhances the photoluminescence characteristics of upconversion phosphors.

Relaxivity tuning of nanomaterials with the intrinsic T1- T2 dual-contrast ability has great potential for MRI applications. Until now, the relaxivity tuning of T1 and T2 dual-modal MRI nanoprobes has been accomplished through the dopant, size, and morphology of the nanoprobes, leaving room for bioapplications. However, a surface engineering method for the relaxivity tuning was seldom reported. Here, we report the novel relaxivity tuning method based on the surface engineering of dual-mode T1- T2 MRI nanoprobes (DMNPs), along with protein interaction monitoring with the DMNPs as a potential biosensor application. Core nanoparticles (NPs) of europium-doped iron oxide (EuIO) are prepared by a thermal decomposition method. As surface materials, citrate (Cit), alendronate (Ale), and poly(maleic anhydride- alt-1-octadecene)/poly(ethylene glycol) (PP) are employed for the relaxivity tuning of the NPs based on surface engineering, resulting in EuIO-Cit, EuIO-Ale, and EuIO-PP, respectively. The key achievement of the current study is that the surface materials of the DMNP have significant impacts on the r1 and r2 relaxivities. The correlation between the hydrophobicity of the surface material and longitudinal relaxivity ( r1) of EuIO NPs presents an exponential decay feature. The r1 relaxivity of EuIO-Cit is 13.2-fold higher than that of EuIO-PP. EuIO can act as T1- T2 dual-modal (EuIO-Cit) or T2-dominated MRI contrast agents (EuIO-PP) depending on the surface engineering. The feasibility of using the resulting nanosystem as a sensor for environmental changes, such as albumin interaction, was also explored. The albumin interaction on the DMNP shows both T1 and T2 relaxation time changes as mutually confirmative information. The relaxivity tuning approach based on the surface engineering may provide an insightful strategy for bioapplications of DMNPs and give a fresh impetus for the development of novel stimuli-responsive MRI nanoplatforms with T1 and T2 dual-modality for various biomedical applications.

Lanthanide (LN)-doped magnetite (Fe3O4) nanoparticles (NPs) were prepared initially as seeding materials, which was followed by the reduction of Au acetate on the surface of the core to produce LN: Fe3O4@Au core@shell NPs. The magnetite NPs were doped with gadolinium (Gd) and europium (Eu) to obtain Gd:Fe3O4 and Eu:Fe3O4, respectively. Transmission electron microscopy (TEM) revealed Gd:Fe3O4, Eu:Fe3O4, Gd:Fe3O4@Au, and Eu:Fe3O4@Au with mean diameters of 6.4, 5.7, 8.4, and 8.9 nm, respectively. X-ray photoelectron spectroscopy showed that Gd or Eu was present in the doped core NPs, respectively. TEM, X-ray diffraction and ultraviolet-visible spectroscopy showed that the core NPs were well coated with Au shells. The magnetic properties of the core NPs and core@shell NPs were characterized by recording the M-H and M-T curves. The magnetically engineered core@shell NPs may have potential bioapplications that may require both magnetic and plasmonic properties. (C) 2016 Elsevier B.V. All rights reserved.

The influence of precursor stack structure on the formation of CuInSe2 (CIS) thin films was investigated by structure characterization of samples with single and multiple InSe/CuSe bilayer stacks deposited by co-evaporation on Mo/glass substrates. With an increase in the number of stacks, the temperature for complete grain growth decreased, but the grain size in the resulting CIS thin films was small. The low crystallization temperature could be attributed to the low activation energy for nucleation, which in turn afforded a nanocrystalline CIS phase even during low-temperature evaporation. Because of the large grain size (1.3μm) in the resulting CIS film and low crystallization temperature, the precursor structure with two alternating InSe/CuSe stacks was concluded to be optimal for solar cell applications; such a structure would have the appropriate number of nucleation sites for complete CIS crystallization to afford a large grain size.

Solar cell modules mainly consist of EVA film and a metal grid. The EVA film is used as waterproof and UV-resistant, which makes it an ideal adhesive film for solar modules installed outdoors. As well, standard crystalline solar cells are generally fabricated with the front grid pattern of silver paste contact. Metal grid cannot help accompanying with shading losses caused by the presence of metal on the top surface of the solar cell, which prevent light from entering the solar cell. The shading losses are determined by the transparency of the top surface, which, for a planar top surface, is defined as the fraction of the top surface covered by metal. In order to fabricate highly efficient solar cell devices, the shading losses should be minimized. In this article, a theoretical estimation has been made to construct a morphologically modified configuration of EVA film so as to minimize the shading losses. According to our numerical calculations and optical simulations, by adopting only slightly modifying the EVA film, the transparency of solar cell modules can be significantly increased by as much as 4%.

The plasma reduction process for the production of reduced graphene oxide (rGO) requires precise process control in order to avoid the degradation of electrical characteristics. We report that the reduction status of the graphene oxides could be determined by monitoring the optical emission intensity at 844.6 nm. Properties of the rGO samples processed with various plasma exposure times were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, and 4-point probe measurements. Optimum electrical performance and surface morphology were obtained from the sample for which the reduction process was stopped when the emission intensity at 844.6 nm began to decrease.

Epitaxially grown CdS thin films on ITO substrates are prepared by using the chemical bath deposition method. As-deposited films are annealed in Ar at 450 degrees C for 6 h and 24 h and the effect of annealing on structural and morphological properties are studied. From the psi rocking curves of high resolution x-ray diffractometer, one can find that after annealing, the metastable nanocrystallite cubic phase transforms into the stable crystalline hexagonal phase, in which its behavior depends on the exposure time to heat. Experimental data revealed that alpha-CdS thin films were crystallized at an initial stage of annealing and that after crystallization, the phase transition from a to beta-CdS took place. STEM microscopy clearly shows the morphological change of as-deposited and annealed CdS thin films.

External-biased potential distributions of a polymer bulk-heterojunction (BHJ) solar cell, incorporated with electron/hole transporting layers, were directly obseved through a cross-sectional Kelvin probe force microscopy. The bulk electric field of BHJ was found to be nearly field-free even under reverse biases, and the field-free region was probed to expand with the incorporation of TiOx electron transporting layer; as a result, inducing a decrease of quasi-Fermi level splitting region in obtaining a high fill factor in the TiOx-interlayered junction photodiodes.

In order to investigate the effect of CdCl2 heat treatment on the physical properties of CdTe thin films grown by a sputtering method, the CdTe thin films were coated with CdCl2. The recrystallization, grain growth, randomization, and reaction kinetics were investigated by monitoring the phase transition of CdCl2-heat-treated CdTe specimens during temperature ramp annealing or isothermal soaking by using in-situ time-resolved high-temperature X-ray diffraction. The results of annealing show that the recrystallizations of CdTe (1 1 1) and other planes do not occur simultaneously, but sequentially in terms of temperature. The results of isothermal soaking imply that the Avrami diffusion-controlled reaction model fits well with the experimental data. This proves that the CdCl2 diffusion process is the dominant factor in the CdTe recrystallization mechanism.

Ultrasonical colloid chemistry deposition (UCCD) has been widely used to fabricate columnar-structured cadmium sulfide (CdS) thin films with ultra-fine particles. In conventional UCCD, the ultrasonic source is installed outside the reaction bath. In this study, an ultrasonic homogenizer was used as the ultrasonic source and was immersed directly in the bulk solution. The advantages of the ultrasonic homogenizer include homogeneous deposition, fine mixing, and enhancement of the ion-by-ion reaction. We compared the physical properties of CdS thin films prepared with and without ultrasound by using an X-ray diffraction, scanning electron microscope, atomic force microscope, and 3D surface analyzer and UV–Vis–NIR measurements.

CdS thin films were grown by a chemical bath deposition method. The physical properties of the CdS thin films were investigated depending on the various processing conditions. A surface morphological study was done by atomic force microscope(AFM) and the structural property was investigated by scanning electron microscope(SEM) and transmission electron microscope(TEM) alternating the processing temperature. Optical transmittance measurement was obtained by UV-Vis-NIR spectrometer. From the experimental results, it was confirmed that the kinetics of CdS film growth was associated with the heterogeneous growth mechanism proposed by Ortega-Borges and Lincot. With an appropriate processing temperature of 55°C and with 0.3 mM CdSO4, 0.1 M thiourea (T.U), and 1.5 M mole concentration of ammonia, transparent and high-resistivity CdS thin films resulted with good conformal coverage.

We present results of a signature-based search for new physics using a dijet plus missing transverse energy (E(T)) data sample collected in 2  fb⁻¹ of pp collisions at √s=1.96  TeV with the CDF II detector at the Fermilab Tevatron. We observe no significant event excess with respect to the standard model prediction and extract a 95% C.L. upper limit on the cross section times acceptance for a potential contribution from a nonstandard model process. The search is made by using novel, data-driven techniques for estimating backgrounds that are applicable to first searches at the LHC.

In order to improve the efficiency of a solar cell device, we performed a CdCl2 treatment on a CdTe/CdS heterojunction grown with a sputtering method. The treatment not only used the conventional solution method where the specimen is dipped in CdCl2-methanol solution directly but also used a quasi-gaseous method where the specimen is exposed to the CdCl2 gas vaporized from a quartz vessel containing the CdCl2-methanol solution. The structural, optical and morphological properties were investigated by the help of the X-Ray diffraction, transmission electron microscopy, scanning electron microscopy and UV-Vis-Nir measurements in order to verify the effectiveness of the quasi-gaseous CdCl2 treatment. When all processes were performed under the same conditions except for the CdCl2 treatment, the quasi-gaseous CdCl2 treatment provided results superior to the aforementioned conventional CdCl2 solution treatment in relation to the physical properties of the CdTe/CdS heterojunction.

In order to investigate the effect of CdCl2 heat treatment on the physical properties of the CdTe thin films grown by a sputtering method, the CdTe thin films were coated with CdCl2. The recrystallisation, grain growth and randomization were investigated by monitoring the phase transition of CdCl2 heat treated CdTe specimens during temperature ramp annealed using in situ high-temperature X-ray diffraction. The result shows that the recrystallisation of the CdTe(111) texture and other textures does not occur simultaneously but sequencially. The XRD data shows there was no overlapped temperature region for recrystallisation between (111) and other textures.

CdS thin films of an n-type window layer of the CdTe thin film solar cell were grown by a chemical bath deposition method. The physical properties of the CdS thin films were investigated depending on the various substrates and the stirring speed. Surface morphological study was carried out by the scanning electron microscope and atomic force microscope. The structural property was investigated by using the X-ray diffraction measurement and transmission electron microscopy. The structural characteristic of the CdS films depend on the substrate crystal structure. The stirring speed effect to the kinetics of the CdS film growth proved the heterogeneous growth mechanism proposed by Ortega-Borges and Lincot.