Preparation and luminescent properties of CaF2:Ln3+ (Ln:Er,Er/Yb)/Nafion composite films

In this work, CaF_2:Ln~(3+)(Ln:Er,Er/Yb)/Nafion composite films were prepared using Nafion as modifications and matrices by dripping method. The composite films were characterized by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD) and scanning electron microscopy(SEM). Composite films are transparent and CaF_2:Ln~(3+)(Ln:Er,Er/Yb) nanoparticles are well dispersed in Nafion films.The thicknesses of CaF_2:Er~(3+)/Nafion and CaF_2:Er~(3+),Yb~(3+)/Nafion composite film are about 77 and 73 μm,respectively. The nanoparticles in composite film possess cubic phase. CaF_2:Er~(3+),Yb~(3+)/Nafion composite film has stronger characteristic emission of Er~(3+) around 1530 nm with full width at half-maximum(FWHM) of 73 nm and longer luminescence lifetimes of 22.04 μs(25.03%) and 100.77 μs(74.97%).     

Enhanced visible light photoactivity of TiO2/SnO2 films by tridoping with Y/F/Ag ions

The Y, F, and Ag tridoped TiO₂/SnO₂ composite nanocrystalline film (YFAg–TS) with prominent photocatalytic performance was prepared by the modified sol–gel method and was characterized by utilizing X-ray diffraction (XRD), differential thermal and thermogravimetric (DTA–TG) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) method, ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), and photoluminescence (PL). The XRD and DTA–TG results expose that the YFAg–TS catalyst is a mixed phase consisting of anatase, rutile, and chlorargyrite, which is beneficial to improving the photocatalytic performance of TiO₂. The SEM, TEM, and BET results disclose that the YFAg–TS film has smaller nanoparticles, higher specific surface area, and narrower pore size compared with pure TiO₂ film. The XRD and TEM results exhibit that a part of yttrium can enter the TiO₂ lattice to induce lattice distortion. The XPS results confirm the presence of Y³⁺ state in the YFAg–TS sample, and Y³⁺ ions can act as the trapping site of electrons to expedite the separation of electrons and holes. The UV–vis DRS results reveal that the YFAg–TS film has an obvious absorption edge shift and a narrower bandgap (2.70 eV) compared with pure TiO₂ film. The PL results show that the YFAg–TS film has the highest photogenerated electrons and holes separation efficiency and charges transfer efficiency among all samples. The photocatalytic activity of the YFAg–TS was assessed by monitoring the degradation of methyl green and formaldehyde solution. The results manifest that the YFAg–TS film has high stability and excellent photocatalytic performance. The possible synergistic photocatalytic mechanism of YFAg–TS films has been discussed in this paper.     

Facile Synthesis of Cu2ZnSnS4 Photovoltaic Absorber Thin Films via Sulfurization of Cu2SnS3/ZnS Layers

Copper zinc tin sulfide (Cu₂ZnSnS₄) has been receiving a lot of attention in recent years as a new, alternative absorber for the production of cheap thin film solar cells owing to the high natural abundance of all the constituents, its tunable direct-band-gap energy, and its large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu₂ZnSnS₄ deposition. In this study, Cu₂ZnSnS₄ thin films were grown on soda lime glass substrates via the sulfurization of solution grown Cu₂SnS₃/ZnS stacked sulfide layers. A new facile route to overcome the difficulty of depositing Cu₂ZnSnS₄ thin film with a desired stoichiometric composition in a single cation solution has been presented. The influences of deposition cycles of layers on the morphological, compositional, structural, and optical properties of the samples were investigated. It was observed from scanning electron microscopy (SEM) images that the films were continuous and composed of homogenously distributed large grains. Possible chemical formulations of the best samples were predicted to be Cu_1.99Zn_1.25Sn_1.00S_3.76 and Cu_1.97Zn_1.03Sn_1.29S_3.71 via energy-dispersive X-ray spectroscopy (EDXS) results. The X-ray diffraction (XRD) patterns of the samples matched very well with the reference values. The Raman-scattering analysis of the films proved the phase purity of the CZTS samples. The optical absorption coefficient of the films was found to be about 10⁴ cm^?1 based on absorbance spectroscopy. The optical band gaps of the films were estimated to be between 1.36 and 1.50 eV. From these we are able to conclude that CZTS thin films can be effectively obtained via the vacuum-atmosphere sulfurization of Cu₂SnS₃/ZnS stacked sulfide layers.     

Intense upconversion luminescence of Er3+/Yb3+ codoped oxyfluoride borosilicate glass ceramics containing Ba2GdF7 nanocrystals

Er3+/Yb3+-codoped transparent oxyfluoride borosilicate glass ceramics containing Ba2GdF7 nanocrystals were prepared and spectroscopic properties of rare earth ions were investigated.Fluoride nanocrystals Ba2GdF7 were successfully precipitated in glass matrix,which was confirmed by X-ray diffraction(XRD)and transmission electron microscopy(TEM)results.In comparison with the as-made precursor,significant enhancement ofupconversion luminescence was observed in the Er3+/Yb3+codoped oxyfluoride glass ceramics,which may be due to the variation of coordination environment around Er3+and Yb3+ions after crystallization.The transition mechanisms of the green and red upconversion luminescence were ascribed to a two-photon process,and that of the blue upconversion luminescence was a three-photon process.     

Corrosion Resistance of Sintered NdFeB Permanent Magnet With Ni-P/Tio22 Composite Film

The Ni-P/TiO₂ composite film on sintered NdFeB permanent magnet was investigated by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), and energy dispersive X-ray spectrometer (EDX). The corrosion resistance of Ni-P/TiO₂ film coated on NdFeB magnet, in 0.5 mol/L NaCl solution, was studied by potentiodynamic polarization, salt spray test and electrochemical impedance spectroscopy (EIS) techniques. The self-corrosion current density (i_corr) and the polarization resistance (R_p) of Ni-P/TiO₂ film are 0. 22 μA/cm² (about 14% of that of Ni-P coating), and 120 kΩ • cm² (about 2 times of that of Ni-P coating), respectively. The anti-salt spray time of Ni-P/TiO₂ film is about 2.5 times of that of the Ni-P coating. The results indicate that Ni-P/Ti0₂ film has a better corrosion resistance than Ni-P coating, and the composite film increases the corrosion resistance of NdFeB magnet markedly.     

A downshifting Eu3+ doped glass embedded with concave pyramid microstructure to improve the efficiency of silicon solar cell

The average photoelectric conversion efficiency (PCE) of a bare mono crystalline silicon solar cell is 14.71% ± 0.03% under AM1.5. It decreases to 14.20% ± 0.005% when covering an un-doped flat glass on the solar cell, and it goes down to 14.10% ± 0.005% by using a 5 wt% Eu³⁺ doped glass. The absorptions of the Eu³⁺ doped CPM glass one-to-one match the excitation spectra at 362, 381, 393, 400, 413 and 464 nm, which are related to the transitions of ⁷F₀→(⁵D₄, ⁵G₂, ⁵L₆, ⁵D₃), ⁷F₁→⁵D₃, and ⁷F₀→⁵D₂, respectively. In addition, a concave pyramid microstructure (CPM) is embedded in the glass surface to increase light transmittance. The average PCE increases to 14.61% ± 0.07% when a 5 wt% Eu³⁺ doped CPM glass covers on the silicon solar cell. Compared with the un-doped flat glass, a net increase of the PCE is 0.41%, where the 0.16% increment of PCE is from the lighting trapping of the CPM structure, and the downshifting of near ultraviolet (NUV) light by Eu³⁺ ion donates the other 0.25% increment. It confirms that the as-prepared Eu³⁺ doped CPM glass has a good downshifting and antireflection function.     

The Effect of Substrate Position during Cylindrical DC Magnetron Sputtering on Physical Properties of Fe7Co3 Thin Film

The high saturation induction makes Fe_1?x Co _x thin films desirable for use as recording head materials. In this experiment, Fe₇Co₃ thin films were deposited by DC cylindrical magnetron sputtering using the different position of glass substrate in argon pressure of 2 × 10^?2 Torr under sputtering power of 120 W. The magnetic properties were determined by scanning probe microscopy. The surface morphology and r.m.s roughness of thin films were analyzed using atomic force microscopy and the optical properties have been analyzed by spectrophotometer. The thin film thickness, grain size and optical properties were affected by changing substrate position and we found the deposition influenced magnetic properties and surface morphology.     

Synthesis and Spectral Properties of Nd^3＋： Gd3Ga5O12 Nanopowder for Transparent Laser Ceramics

Nd^3＋： Gd3Ga5O12（Nd ： GGG） nanopowder for transparent laser ceramics was synthesized using sol-gel method. XRD, SEM, and fluorescence spectrum were used to study the properties of Nd^3＋ ：Gd3Ga5O12 nanopowder. XRD patterns of samples show that it has a cubic structure. Meanwhile, pure Nd：GGG crystals were obtained at 1000 ℃ for 12 h. SEM photographs show that dispersed, uniform, ball-like Nd：GGG nanopowder is obtained. Both XRD and SEM results show that the crystallization degree and the grain size increase with the increase in calcining temperature. Analysis of fluorescence spectrum shows that fluorescence emission occurs at 1062.7 nm, which is the result of Nd^3＋ （^4F3/2→^4I11/2） transition. Homogenous Nd ： GGG nanopewder with a small grain size synthesized using the sol-gel method is favorable for sintering the transparent ceramic, which proves that the nanopewder obtained is suitable as a precursor for preparing GGG transparent ceramics.     

The loss of driving force due to volume diffusion ahead of a migrating boundary in a cellular precipitation reaction

Experimental confirmation has been obtained of the existence of a solute diffusion zone ahead of a migrating cell boundary during the cellular precipitation of Cr₂N in a high nitrogen CrNi austenitic steel. The solute profile has been measured directly using analytical electron microscopy and indirectly by optical microscopy of potentiostatically etched specimens. The width of the diffusion zone was observed to increase with reaction time; this corresponded to the deceleration of the migration rate of the cell boundary with reaction time.     

Al2Ti precipitation in Al64Fe8Ti28 alloy

Precipitates of Al₂Ti with three different stacking sequences have been observed in Fe-modified Ll₂-type ordered Al₃Ti specimens. Two of the stacking sequences have been observed previously. The third type of Al₂Ti, Al₂Ti^III, is identified in this study using conventional and highresolution transmission electron microscopy (TEM). The Al₂Ti precipitates form as plates along {100} planes and compression tests performed at liquid N temperature show microcracks occurring along those {100} planes. The Al₂Ti phase is believed to be responsible for the low cleavage strength that is observed.     

Low temperature strain behavior of Pb thin films on a substrate

The microstructural changes occurring during cooling from 300 to 100 K in a 0.2 μm thick polycrystalline Pb film deposited on a Si₃N₄ substrate were studied by a combination of transmission electron microscopy and X-ray diffraction technique. The tensile strain induced in the film upon cooling due to the thermal expansion coefficient mismatch between the film and the substrate was observed to be relaxed by dislocation glide. Most of the dislocations were observed to glide across the grains on 111 planes that are inclined at an angle of ∼ 70 deg to the film surface, and on 111 planes that are nearly parallel to the film surface. All the dislocation motions are confined in each grain by the surface oxide, the substrate, and grain boundaries. Some observations suggested that these dislocations emanate from grain boundaries. At 100 K, the density of dislocations introduced in the grains with diameters larger than ∼0.6 μm was found to be roughly constant (about 10¹⁰/cm²), while no dislocations were observed in grains smaller than ∼0.6 μm. The observed dislocation density can account for the amount of strain relaxed which was measured by the X-ray diffraction technique. It was also found that almost all the dislocation glide events involved in the thermal cycling process are reversible. This explains a previous X-ray diffraction result that no work hardening effect was observed in Pb films during the thermal cycling at low temperature. The yield stresses of Pb films as determined by the strain measurements are about three times higher than those expected by a simple dislocation pinning model. Based on the dislocation motion observed in this work, the yield stresses of the films were re-evaluated as a function of film thickness and grain size using an energy criterion model. This model took into account the effects of the surface oxide and substrate on dislocation     

Electrical and structural studies on (PEO)50-AgCF3SO3: SnO2 nanocomposite gel polymer electrolyte materials

The present work deals with a new series of silver-ion conducting nanocomposite gel polymer electrolytes based on poly (ethylene oxide)₅₀silver triflate, (PEO)₅₀AgCF₃SO₃ incorporated with a nano-sized inorganic filler namely, SnO₂ and a plasticizer, ethylene carbonate (EC) prepared using solution casting technique. Electrical conductivity measurements have been made on thin film polymer electrolyte systems containing (PEO₅₀AgCF₃SO₃: 2wt% SnO₂) + x wt% EC (x = 10, 15, 20, 25 and 30 respectively). It has been found that the room temperature ionic conductivity value enhanced from 3.1 × 10^?6 to 5.4 × 10^?5 S cm^?1 on addition of EC into the chosen nanocomposite system PEO₅₀AgCF₃SO₃: 2wt% SnO₂. The apparent surface morphology has been examined through scanning electron microscopic (SEM) analysis. The occurrence of a reduction in the degree of crystallinity of the plasticized system has also been revealed from the observed X-ray diffraction (XRD) data.     

Corrosion behavior of austenitic alloy 690 under anodic and cathodic potentials

The corrosion behavior of austenitic alloy 690 in a solution-annealed condition has been evaluated with the application of anodic as well as cathodic potentials in an acidic chloride solution at room temperature (RT). In a 0.5M H₂SO₄ + 0.5M NaCl solution, the alloy displayed active-passive pitting behavior with the application of an anodic potential. Surface films, formed at the onset and later stage of the passive region, were characterized using X-ray photoelectron spectroscopy (XPS). The XPS revealed that the surface film formed at the onset of passivity (+ 100 mV SCE) consisted of Cr(OH)₃, without any Fe⁺³/Fe⁺². The presence of nickel in the film was found in a transition state of Ni⁺² and Ni⁰. The passive film formed at the higher anodic potential (+ 700 mV SCE) consisted of Cr₂O₃ without any Fe⁺³/Fe⁺² or even Ni⁺²/Ni⁰. Microscopic studies of alloy 690 after anodic polarization in an acidic chloride solution revealed pitting, which was found to be initiated at large, faceted TiN-type inclusions. The susceptibility of the alloy to hydrogen embrittlement has been investigated by conducting cathodic charging of the tensile samples in a 0.5M H₂SO₄ solution at RT and by subsequent tensile testing of the charged samples in air at a strain rate of 1.3 × 10⁻⁴ s⁻¹ up to fracture. An indication toward hydrogen-induced ductility loss was noticed for the samples of the alloy, which is believed to be attributable to a hydrogen-enhanced microvoid growth process. Since the microvoid growth process occurs at the last stage of fracture, the effect of hydrogen on the ductility of the alloy is little.     

Influence of short circuiting on the kinetics and mechanism of iodide film growth on Ag and Cd-doped Ag

Results of iodination studies on pure Ag and Ag with 6000 ppm of Cd under normal and short-circuit conditions in the temperature and iodine pressure ranges of 333 to 373 K and 0.067 to 6.078 kPa, respectively, are reported. Under all experimental conditions, the iodide film growth kinetics conform to parabolic rate law. The iodide films have been characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPM), X-ray diffraction (XRD), and Auger electron spectroscopy (AES) analyses. The effect of a higher valent dopant like Cd in Ag is observed to decrease the rate of normal iodination, which suggests that the film growth process is controlled by migration of electron holes across the iodide layers. The presence of a short-circuit path enhances the rate of iodination for pure Ag. However, the iodination rate of Cd-doped Ag under short-circuit mode is found to be further enhanced compared to that for pure Ag. This has been explained on the basis of the ion migration mechanism. The pressure dependence of rate constants is found to follow a relation like k _P α for pure Ag and Cd-doped Ag under normal conditions. The corresponding relations under short-circuit mode are observed to be k _P α and k _P α for Ag and Cd-doped Ag, respectively. Arrhenius plots have yielded activation energy values of 25.8 and 15.2 kJ·mol⁻¹ under normal and short-circuit conditions, respectively. The kinetic results of parabolic film growth have been explained with the help of defect equilibria, considering the predominance of Frenkel defects in pure and doped AgI lattices. The mechanism of film growth processes has been confirmed to be Wagner’s electrochemical potential gradient-induced migration of defect species across the iodide layer.     

Up-conversion of Er3＋/yb3＋ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals

The up-conversion of Er3+/Yb3+co-doped transparent glass-ceramics 50SiO2-10AlF3-5TiO2-30BaF2-4LaF3-0.5ErF3-0.5YbF3 containing Ba2 LaF7 nanocrystals under the changing of heat treatment temperature and time were investigated.The Ba2 LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction(XRD).The structural investigation carried out by XRD and transmission electron microscopy(TEM) evidenced the formation of cubic Ba2 LaF7 nanocrystals with crystal size of about 14 nm.Comparing with the samples before heat treatment,the high efficiency up-conversion emission of Er3+/Yb3+co-doped samples was observed in the glass-ceramics under 980 nm laser diode excitation.The increase in red emission intensity bands was stronger than the green bands when the crystal size increased.The mechanism for the up-conversion process in the glass-ceramics and the reasons for the increase of Er3+/Yb3+co-doped up-conversion intensity after heat treatment were discussed.     

Upconversion hollow nanospheres CeF3 co-doped with Yb3+ and Tm3+ for photocatalytic nitrogen fixation

Solar driven nitrogen (N₂) fixation to synthesize ammonia is a potential alternative for the traditional Haber-Bosch approach to meeting industrial demand, but is largely hampered by the difficulties in the harvesting of solar energy and activating inert N₂. In this work, hollow CeF₃ nanospheres co-doped with activator Tm³⁺ and sensitizer Yb³⁺ (Yb³⁺:Tm³⁺:CeF₃) were prepared by microwave hydrothermal method. The product was employed as a catalyst for photo-driven N₂ fixation by adjusting the molar ratio of Ce³⁺:Yb³⁺:Tm³⁺. Results show that the porous hollow structure enhances the light-harvesting by physical scattering and reflection. In addition, heteroatom doping generates abundant fluorine vacancies (F_V) which provide abundant active sites for adsorption and activation of N₂. The sample with molar ratio of CeF₃:Yb³⁺:Tm³⁺ at 178:20:2 demonstrates the highest utilization of solar energy attributed to the strongest upconversion capability of near-infrared (NIR) light to visible and ultraviolet (UV) light, and the NH₄⁺ concentration achieves the highest value of 15.06 μmol/(g_cat?h) under simulated sunlight while nearly 6.22 μmol/(g_cat?h) under NIR light. Current study offers a promising and sustainable strategy for the fixation of atmospheric N₂ using full-spectrum solar energy.     

Kinetics of oxide formation in liquid copper and silver

The process of formation of oxide phases in liquid copper and liquid silver has been studied by pumping oxygen into the liquid alloy with the use of a solid-electrolyte electrochemical cell. The oxygen potential at the electrolyte-metal interface is monitored simultaneously by the electrochemical cell. A wide range of effects were observed ranging from the very rapid formation of a layer of oxide at the electrolyte-metal interface to what appears to be homogeneous nucleation of the oxide in the metal. The results may help to explain some of the difficulties that sometimes have been observed in using this type of cell to measure the oxygen potential of a liquid metal. The results indicate that a supersaturation ratio of about 9 is necessary for homogeneous nucleation of iron oxide (most probably Fe₃O₄(s)) in liquid copper containing 0.01 to 0.07 pct iron. The interfacial tensionσ _{Cu-Fe 3}O₄ is calculated to be 0.74 J/m². In experiments with higher concentrations of deoxidant (0.2 pct Fe in Cu and 0.2 to 0.4 pct Ni in Ag) equilibrium precipitation of oxides apparently predominates over homogeneous nucleation for the experimental conditions employed. A mathematical model which partly explains the different effects observed is presented.     

Synthesis of CeO_2/fly ash cenospheres composites as novel photocatalysts by modified pyrolysis process

A novel fly ash cenospheres(FACs)-supported CeO2 composite(CeO2/FACs) was successfully synthesized by the modified pyrolysis process.The prepared composites were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), and diffuse reflection spectra(DRS) techniques.XRD results indicated that the CeO2 film coated on cenospheres was a face-centered cubic structure.SEM images confirmed that the CeO2 film was relatively compact.XPS results showed that Ce was present as both Ce4+ and Ce3+ oxidation states in CeO2 film coated on FACs substrate.The bandgap of the composite was narrower compared with the pure CeO2.The as-prepared material exhibited good photocatalytic activity for the decolorization of methylene blue(MB) under visible light irradiation, and the first-order reaction rate constant(k) of 0.0028 min–1 for CeO2/FACs composite was higher than 0.0015 min–1 of pure CeO2.The fact that they floated on water meant that CeO2/FACs composites were easily recovered from water by filtration after the reaction.The recycling test revealed that the composites were quite stable during the MB photocatalytic decolorization.The CeO2/ FACs catalyst was therefore promising for practical use in the degradation of pollutants or water cleanup.     

Studies on the effect of addition of silver ions on the direct oxidation of pyrite

The nature of the reaction between Ag⁺ and pyrite in 0.25 M H₂SO₄ solutions has been investigated in order to determine whether Ag⁺ can enhance the ferric sulfate leaching of this mineral. Analysis of reacted pyrite particles using scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and low-angle X-ray diffraction (XRD) indicates that elemental silver and elemental sulfur are the primary surface species formed by this interaction. Rest potential measurements of a pyrite electrode immersed in a solution containing 10⁻² M Ag⁺ are also consistent with what is expected for the deposition of metallic silver. Furthermore, the XRD data reveal that, at the most, only minor amounts of Ag₂S are being produced. The presence of Ag₂O has also been detected, but this is due to oxidation of silver after the experiment is complete and while the particles are being transferred for surface analysis. When 1 M ferric sulfate is contacted with pyrite which has been pretreated in a AgNO₃ solution, most of the silver immediately redissolves and does not redeposit while ferric ions are present. This indicates that the kinetics of the transfer reaction between Ag⁺ and pyrite is slower than the reaction between Fe³⁺ and pyrite and suggests that Ag⁺ does not likely enhance the ferric sulfate leaching.     

Corrosion resistance of new copper alloy containing 29Zn, 10Ni and up to 5Mn vis-a-vis Cu-10Ni in sulphide polluted synthetic seawater

Cu-10 Ni alloy suffers from accelerated corrosion in sulphide-polluted seawater. New copper alloys containing 29% Zn, 10Ni and 3 or 5% Mn have been found to be more corrosion resistant than Cu-10Ni alloys in sulphide polluted synthetic seawater. The studies were carried out in synthetic seawater (ASTM D 114–75) and sulphide was added through Na₂S (1 gpl ≈ 41ppm S²⁻). Testing was carried out using cathodic and anodic potentiodynamic polarization methods. Corrosion product film formed on the Cu-29Zn-10Ni-5Mn alloy in sulphide polluted synthetic seawater was characterized using SEM and XRD. The film was found to contain Cu₂O, Cu₂S, NiS and ZnS. Better corrosion resistance of new alloys as compared to that of Cu-10Ni alloy is attributed to formation of ZnS, a bad conductor, in the film and incorporation of Mn³⁺ cations in Cu₂O and Cu₂S lattice.