Effects of intermediate energy heavy‐ion irradiation on the microstructure of rutile TiO2 single crystal

This study reports the microstructure evolution of single crystal rutile TiO₂ under 3 MeV Nb⁺ ion irradiation, with the irradiating ions incident on the {100} plane. A complex, multi‐layered microstructure evolution is observed with 4 distinct regions: (i) short‐range disorder in the first 60 nm below the specimen surface, (ii) dislocation loops oriented parallel to the incident ion beam direction, located along the increasing slope of the irradiation damage profile at ~60‐650 nm from the surface, (iii) loops oriented perpendicular to the incident ion beam direction, at depths encompassing the ion implantation and irradiation damage peaks ~650‐1250 nm, and (iv) a high density of nano‐scale atomic rearrangements with long‐range order, located at depths ~1250‐1750 nm. These results present evidence that multiple defect mechanisms occur during irradiation including ion channeling, nuclear stopping, and electronic stopping interactions as a function of depth and disorder accumulation.     

Phase‐dependent radiation‐resistant behavior of BaTiO3: An in situ X‐ray diffraction study

The radiation‐resistant response of BaTiO₃ in the tetragonal and rhombohedral phases on exposure to 100 MeV Ag⁷⁺ ion irradiation was investigated by in situ X‐ray diffraction (XRD) at room temperature (300 K) and low temperature (25 K), respectively. This study revealed that the BaTiO₃ in rhombohedral phase retained crystallinity up to an ion fluence of 1×10¹⁴ ions/cm², whereas tetragonal phase amorphized at much lower fluence viz. 1×10¹³ ions/cm². The in situ XRD along with Raman spectroscopy studies revealed that BaTiO₃ in rhombohedral phase is more radiation resistant than that of tetragonal phase. The density functional theory (DFT) calculations confirmed higher bond strength of rhombohedral phase as compared to tetragonal phase, which supported the experimental result of higher radiation stability of rhombohedral phase. The theoretical predictions on high‐temperature phase will be of relevance to the nuclear waste applications.     

Far‐Red‐Emitting BiOCl:Eu3+ Phosphor with Excellent Broadband NUV‐Excitation for White‐Light‐Emitting Diodes

Rare‐earth ion‐doped semiconducting phosphor has attracted extensive attention due to the ability to achieve efficient luminescence through the host sensitization. Here, we present a new type red‐emitting Eu³⁺ ‐doped BiOCl phosphors possessing a broad excitation band in the near‐ultraviolet (NUV) region. Experimental measurements and theoretical calculations confirm that Eu³⁺ ion dopants result in forming impurity energy level near valence band, and the excellent broadband NUV‐exciting ability of Eu³⁺ ion is due to the electronic transitions of BiOCl band gap. Moreover, the highest emission intensity of the phosphors is from the ⁵D₀ → ⁷F₄ transition of Eu³⁺ around 699 nm (far‐red) through whether host excitation or direct Eu³⁺ ions excitation, which lie in the particular structure of BiOCl crystals. Our results indicate that the Eu³⁺ ‐doped BiOCl crystals show great potential as red phosphors for white‐light‐emitting diodes.     

Nanowire Growth by an Electron‐Beam‐Induced Massive Phase Transformation

Tungsten trioxide nanowires of a high aspect ratio have been synthesized in situ in a TEM under an electron beam of current density 14 A/cm² due to a massive polymorphic reaction. Sol–gel‐processed cubic phase nanocrystals of tungsten trioxide were seen to rapidly transform to one‐dimensional monoclinic phase configurations, and this reaction was independent of the substrate on which the material was deposited. The mechanism of the self‐catalyzed polymorphic transition and accompanying radical shape change is a typical characteristic of metastable to stable phase transformations in nanostructured polymorphic metal oxides. The findings are important to the controlled electron beam deposition of nanowires for functional applications starting from colloidal precursors.     

In‐Situ Reactor Radiation‐Induced Attenuation in Sapphire Optical Fibers

The purpose of this work was to determine the suitability of using instrumentation utilizing sapphire optical fibers in a nuclear reactor environment. In this work, the broadband (500–2200 nm, or 0.56–2.48 eV) optical transmission in commercially available sapphire optical fibers was monitored in‐situ prior to and during reactor irradiation. The sapphire fibers were irradiated at a neutron flux of 1.5 × 10¹² n/(cm²·s) and a gamma dose rate of 75 kGy/h (dose in sapphire) to a total neutron fluence of 1.1 × 10¹⁷ n/cm² and total gamma dose of on the order of 1.5 MGy. Consistent with previous gamma irradiation experiments, an absorption band centered below 500 nm (the minimum measurable wavelength using the measurement system described in this work) and extending as far as ~1000 nm reached saturation during irradiation in the gamma shut‐down field (the gamma‐ray radiation field that is present in the reactor post‐operation, as a consequence of the decay of radioisotopes that were produced during reactor operation) of the reactor prior to reactor irradiation. Beginning reactor irradiation and increasing the reactor power caused rapid increases in attenuation, followed by a linear increase with irradiation time at constant reactor power. Shutting down the reactor caused a decrease in the added attenuation; however, restarting the reactor caused the added attenuation to rapidly return to values almost identical to those observed at the end of the previous irradiation. The decrease in attenuation that was observed after the reactor was shut down shows the importance of the in‐situ nature of the measurements made in this work (previous ex‐situ attenuation measurements could not have captured this effect). A model is proposed for the experimentally obtained values of the radiation‐induced attenuation that involves three previously identified color centers including a composite V‐center, a center, and a center. The model accounts for gamma radiation‐induced ionization of pre‐existing defects, generation of new defects via displacement damage, and conversion between defect centers via ionization and charge recombination.     

A Novel Blue‐Emitting Phosphor of Eu2+‐Activated Magnesium Haloborate Mg3B7O13Cl

Eu²⁺‐doped magnesium haloborate Mg₃B₇O₁₃Cl was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction (XRD) measurements and structure refinement. The photoluminescence excitation and emission spectra, and decay curves were measured. Under the excitation of near‐UV light, Eu²⁺‐doped Mg₃B₇O₁₃Cl presents a narrow blue‐emitting band centered at 423 nm. The maximum absolute quantum efficiency (QE) of Mg₃B₇O₁₃Cl:Eu²⁺ phosphor was measured to be 80% excited at 385 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects. Moreover, Mg₃B₇O₁₃Cl:Eu²⁺ phosphor shows scintillation characteristics excited by X‐ray irradiation at room temperature and presents a blue luminescence band with a fast lifetime of 600 ns.     

Additive‐Free Synthesis of Cerium Oxide Nanorods with Reaction Temperature‐Tunable Aspect Ratios

The ability to control the morphology of fluorite‐structured cerium oxide nanomaterials is an important step in the design of cerium oxide‐based catalysts. Herein, we report an additive‐free synthesis of cerium oxide nanorods with highly tunable aspect ratios from ~6:1 to 40:1. The use of a microwave hydrothermal method allows for both rapid synthesis and temperature control. The ability to control the length of the nanorods from <51 nm to >1.7 μm by varying only the reaction temperature was demonstrated over a temperature range of 80°C to 200°C. The formation of the resulting nanorods was investigated using selected‐area electron‐diffraction and high‐resolution transmission electron microscopy. The surface area of nanorod products was found to decrease from 117 to 22 m²/g as the reaction temperature increased from 80°C to 200°C, complementing the general trend of the increasing aspect ratios of these products.     

Cr3+‐activated Li5Zn8Al5Ge9O36: A near‐infrared long‐afterglow phosphor

Near‐infrared long‐afterglow (LAG) materials have attracted considerable attention owing to their high potential for in vivo imaging applications. Here, we present a series of near‐infrared LAG phosphors Li₅Zn₈Al_5?xGe₉O₃₆:xCr³⁺ (LZAG:Cr³⁺), which were synthesized using a solid‐state reaction method. The pure LZAG host exhibits blue photoluminescence and LAG emission. We investigated the effect of the zinc vacancy contents on the photoluminescence and LAG performance by adjusting the zinc content and introducing Ga³⁺ ions to substitute the Zn²⁺ sites in LZAG host. When Cr³⁺ ions were introduced into the LZAG host, LZAG:Cr³⁺ produced a strong, broad blue emission band centered at 456 nm and a near‐infrared emission band at 700 nm caused by the ²E → ⁴A₂ transition of Cr³⁺. The energy transfer processes from the LZAG host to Cr³⁺ were identified in the photoluminescence and LAG process. After irradiation at 258 nm for 10 minutes, the LAG emission of LZAG:0.008Cr³⁺ can last nearly 2.5 hours. Moreover, the LAG intensity and duration of LZAG: 0.008Cr³⁺ were significantly improved by introducing a small dose of Ga³⁺ ions. Finally, the traps and mechanism of LAG in LZAG, LZAG:Ga³⁺, and LZAG:Cr³⁺ were discussed in detail.     

Cr‐doped ZnAl2O4: Microwave solution route for ceramic nanoparticles from metalorganic complexes in minutes

A combination of microwave irradiation and metalorganic precursors in solution was used for the synthesis of Cr:ZnAl₂O₄ nanoparticles with high yields (~92%). Though the spinel phase is formed after ~40 minutes, 60 minutes of microwave irradiation was required for the complete transformation of precursors into the spinel. The as‐prepared material is nanocrystalline and phase‐pure and was subjected to annealing in air at different temperatures. Annealing improved the crystallinity, and the material turned pink at 1200°C. The structural and optical properties were investigated by XRD, HR‐TEM, FE‐SEM, FT‐IR, diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The two bands in the excitation spectra (400 and 540 nm) became more intense as the annealing temperature was raised. The 400 nm band was asymmetric and consisted of two peaks, suggesting a trigonal distortion. The emission spectra consisted of a zero phonon line (ZPL), along with its associated multi‐phonon side bands. The high Dq/B (3.21) suggested the presence of Cr³⁺ in a strong crystal field. With annealing, the emission lifetimes increased from ~7 to ~34 ms. This work demonstrates rapid, low‐temperature synthesis of a red‐emitting phosphor, with potential applications in bio‐imaging, sensors, and lighting.     

Radiation Stability of Spark‐Plasma‐Sintered Lead Vanadate Iodoapatite

Spark‐plasma‐sintered lead vanadate iodoapatite Pb_9.85(VO₄)₆I_1.7, a promising nuclear waste form for the immobilization of I‐129, was irradiated with energetic ions, electrons, and gamma rays, to investigate its radiation stability. In situ TEM observation of the 1 MeV Kr²⁺ irradiation shows that lead vanadate iodoapatite generally exhibits higher tolerance against ion irradiation‐induced amorphization than lead vanadate fluorapatite, and the spark plasma sintering can further enhance its radiation stability attributed to the enhanced crystallinity, reduced defect concentration, and denser microstructure. The critical amorphization dose and critical temperature for the SPS‐densified iodoapatite at 700°C are determined to be 0.25 dpa at room temperature and 230°C, respectively. No significant phase transformation or microstructural damage occurred under energetic electron and gamma irradiations. Raman spectra of gamma‐ray‐irradiated iodoapatite indicate improved V–O bond order at 500 kGy dose. Generally, the spark‐plasma‐sintered iodoapatite exhibits excellent radiation stability for nuclear waste form applications. The significantly enhanced radiation stability of the SPS‐densified iodoapatite suggests that SPS holds great promise for fabricating iodoapatite waste form with minimum iodine loss and optimized radiation tolerance for effective management of highly volatile I‐129.     

Emergence of defect fluorite structure in nano‐sized thoria through doping with some divalent transition‐metal ions

With the objective of incorporating some divalent transition‐metal ions in thoria and to comprehend its effect on the crystal structure, electronic as well as catalytic properties, Ni²⁺, Cu²⁺ and Cd²⁺ substituted thoria samples were synthesized by the epoxide gel method. Of the two concentrations investigated, 10 mol% of Ni²⁺, Cu²⁺, and Cd²⁺ could be substituted retaining the fluorite structure and phase separation into individual oxides was noticed for 15 mol%. The average crystallite size of thoria and 10 mol% substituted samples was 14 nm. Le‐Bail structural refinements of Powder X‐ray diffraction (PXRD) patterns indicated marginal increase in unit cell constant for the Cd²⁺ substituted sample and a decrease for Ni²⁺ and Cu²⁺ substituted samples. In addition to broadening of the band at around 460 cm^?1 (F_2g vibration of the fluorite), less intense band near 560‐590 cm^?1 emerged for all the transition‐metal ion‐containing samples in the Raman spectra implying the formation of oxygen defects. The absorption edge in the UV‐visible spectra moved toward higher wavelength for Cd²⁺, Ni²⁺ and Cu²⁺ containing samples as compared to pure thoria. In addition, d‐d transition was observable for Ni²⁺ and Cu²⁺ containing samples. By virtue of these changes in the electronic structure of transition‐metal ion‐containing samples, they were examined as catalysts for the degradation of aqueous Rhodamine‐6G (Rh‐6G) dye solutions under visible radiation.     

Hydronium Ions in Soda‐lime Silicate Glass Surfaces

The presence of leachable alkali ions, or their hydrated sites in the glass, is believed to be a determining factor for the interfacial water structure at the glass surface, influencing the surface properties of glass. The interfacial water structure on soda‐lime silicate glass in humid ambience at room temperature was analyzed with sum‐frequency‐generation (SFG) vibration spectroscopy, which can probe the interfacial water layer without spectral interferences from the gas phase water. The soda‐lime glass surface exposed to water vapor shows three sharp SFG peaks at 3200, 3430, and 3670 cm^?1 in SFG, which is drastically different from the SFG spectra of the water layers on the fused quartz glass surface and the liquid water/air interface. The sharp peak at 3200 cm^?1 is believed to be associated with the hydronium ions in the Na⁺‐leached silicate glass surface. The 3200 cm^?1 peak intensity varies with the relative humidity, indicating its equilibrium with the gas phase water. It is proposed that the hydronium ions in the Na⁺‐leached sites produce compressive stress in the silicate glass surface; thus the growth of hydronium ions with increasing humidity might be responsible for the increased wear resistance of soda‐lime glass surfaces in near‐saturation humidity conditions.     

Viscosity and Fragility of Alkaline‐Earth Sodium Boroaluminosilicate Liquids

Understanding the composition and temperature dependence of viscosity of silicate liquids is of the highest importance not only for geological processes but also for production of industrial glass. In this work, we have determined the temperature dependence of equilibrium liquid viscosity of 36 alkaline‐earth sodium boroaluminosilicate liquids as a function of the Si/Al ratio and the type of alkaline‐earth oxide (MgO, CaO, SrO, or BaO). We demonstrate that the isokom temperature at 10¹² Pa s (i.e., the glass transition temperature) generally increases with increasing Si/Al ratio, whereas the isokom temperatures at 10⁴ and 10^1.5 Pa s exhibit a decrease with increasing [Al₂O₃] in the peraluminous regime. The isokom temperatures decrease with increasing alkaline‐earth size in the peralkaline regime, whereas they increase with increasing alkaline‐earth size in the peraluminous regime. The liquid fragility index m exhibits a minimum value at an intermediate Si/Al ratio, with the position of the minimum increasing to a higher value of [Al₂O₃] with increasing alkaline‐earth size. We have discussed our findings in terms of the underlying structural and topological changes as a function of composition and temperature.     

Multi‐Site and Multi‐Ionization of Sn in the Doping of BaTiO3

This article considers the diverse substitutional effects of the Sn cations in the BaTiO₃ lattice and its impact on the electrical conduction as a function of A/B stoichiometry, oxygen partial pressure, and temperature. High‐density specimens were fabricated in the different oxygen partial pressures to control the valence state of Sn ion. Specifically, the nonstoichiometric materials were sintered in a low pO₂ atmosphere (10^?14 atm at 1320°C) and in a high pO₂ atmosphere (10^?0.21 atm at 1320°C), respectively. It is found that Sn occupying the Ti‐site acts as an acceptor dopant, and the electronic conductivity varies from a n‐type to p‐type transition, with increasing oxygen activity as mostly expected. However, there is an unusual case noted with Sn doping the A‐site where the conductivity, σ, is invariant at high pO₂'s, i.e., σ ~  with m ≈ 0 in the high pO₂ regime. The variation of the conductivity is explained by a valence changing of Sn ion from +2 to +3 to +4 with increasing oxygen partial pressure, and we model this data across all conditions within a self‐consistent defect chemistry model.     

Ion beam deposition of amorphous hydrogenated carbon films on amorphous silicon interlayer: Experiment and simulation

A thick layer of amorphous silicon (a-Si) was deposited on industrial grade crystalline n-Si < 111 > substrate by means of electron beam evaporation. On top of a-Si layer, amorphous hydrogenated carbon (a-C:H) film was grown by direct ion beam deposition from acetylene precursor gas. In order to study on atomic level the a-C:H film growth on amorphous silicon, a theoretical model was developed in a form of reaction rate (kinetic) equations. Numerical simulation using this model has revealed that the ratio of sp³/sp² content in the film is heavily influenced by relaxation rate of the carbon atoms in a sub-surface region of the film that were activated by ion irradiation. The final structure of a-C:H film does not depend much on elemental composition and structure of amorphous Si coating, provided that deposition procedure is not terminated at its initial stage but continues for more than 60 s. It became evident, therefore, that the use of a-Si interlayer with a-C:H films could be particularly beneficial when a need arises to minimize or eliminate the effect of the substrate. As one of such cases, a poor adhesion of amorphous carbon on steel and other ferrous alloys could be mentioned.     

Cathodoluminescence Properties of Blue Emitting Eu2+‐Doped AlN‐Polytypoids for Field‐Emission Displays

Eu²⁺‐doped AlN‐polytypoids (8H, 15R, 12H, and 21R) were successfully synthesized by nitrogen‐gas‐pressure sintering. The phosphors show intense blue emissions under the electron beam excitation. All the polytypoid phosphors exhibit relatively a smaller degradation in luminance and a higher thermal stability in comparison to the oxide counterparts. Among the polytypoids, 12H has no luminance saturation, and shows a brightness of 40 cd/m² at 3 kV and 100 μA. These results indicate that Eu²⁺‐doped AlN‐polytypoids could also be used as blue phosphors for FEDs.     

CaO‐containing LaCO3OH nanogears and their luminescence and de‐NOx properties

Large‐scale, uniform, monodisperse LaCO₃OH cherry‐blossom‐like nanogears and/or nanocubes have been synthesized under hydrothermal reaction conditions. Upon the addition of only 5 mol% Ca²⁺ ions into a La nitrate salts solution with pH 8.5, LaCO₃OH crystals with novel cubic or nanogear structures are formed in the hexagonal phase. The hydrothermal reactions were carried out without the addition of a template or catalysts. Both 24 hour and 48 hour hydrothermal reactions yield 100% pure LaCO₃OH with no irregular particles. We examined the photoluminescence properties of the as‐synthesized powders of the pure LaCO₃OH nanogears and found one broad emission band centered at 394 nm after excitation at λ  =  280 nm. The NO reduction activity was also examined over highly dispersed CaO‐containing La₂O₃ obtained after calcination the LaCO₃OH at 800^○C for 2 hours. The CaO‐containing La₂O₃ catalysts showed good stability for NO reduction with CH₄ in the presence of O₂ and H₂O vapor.     

NaBaY(BO3)2:Ce3+,Tb3+: A novel sharp green‐emitting phosphor used for WLED and FEDs

A new borate phosphor NaBaY(BO₃)₂: Ce³⁺, Tb³⁺ (NBY:Ce³⁺, Tb³⁺) was successfully synthesized under low temperature designed to put into application in the fields of ultraviolet (UV)‐excited light emitting diodes (LEDs) and field emission displays (FEDs). The structure distortion between Ce³⁺, Tb³⁺ single‐ and co‐doping NBY was discussed by X‐ray powder diffraction Rietveld refinement, high‐resolution transmission electron microscopy (HRTEM) and spectra. NBY: Ce³⁺, Tb³⁺ presents a wide absorption band ranging from 310 to 400 nm and efficient green emission (λ_max = 542 nm) with a full‐width at half‐maximum of 3.3 nm. The remarkable thermal stability has also been tested, indicating that the intensity at 200°C is still beyond 70% of the original intensity. In addition, a white LED device was manufactured by connecting a 370 nm UV chip with a blend of BaMaAl₁₀O₁₇: Eu²⁺ (BAM: Eu²⁺), NBY: Ce³⁺, Tb³⁺ and CaAlSiN₃: Eu²⁺. The color coordinate, correlated color temperature and color rendering index of the manufactured LED device were (0.335, 0.347), 5511 K and 80.16, respectively. Meanwhile, the cathodoluminescence (CL) spectra under the various conditions of probe currents and accelerating voltages were also analyzed. Through successive excitation of low‐voltage electron‐beam, the wonderful performances of degradation property and color stability were obtained. These results suggest that the green‐emitting NBY: Ce³⁺, Tb³⁺ phosphor has the prospect of becoming applications in white UV LEDs and FEDs.     

BaCl2:Er3+—A High Efficient Upconversion Phosphor for Broadband Near‐Infrared Photoresponsive Devices

Utilization of photons with subband‐gap energy, mostly near‐infrared (NIR) photons, is highly desirable for photovoltaic cells; which can be achieved by adding an upconversion layer at the rear face of photovoltaic cells. Here, we study the upconversion luminescence properties of BaCl₂:Er³⁺ phosphors and hexagonal NaYF₄:Er³⁺ phosphors upon excitation of incoherent NIR sunlight with wavelength λ > 800 nm. Higher efficacious upconversion emissions of BaCl₂:Er³⁺ phosphors have been observed in comparison with the well‐known hexagonal NaYF₄:Er³⁺ phosphors. We demonstrate that the photocurrent response from the thin‐film‐hydrogenated amorphous silicon solar cell attached with the BaCl₂:Er³⁺ phosphor is notably enhanced under irradiation of incoherent NIR sunlight with wavelength λ > 800 nm. This judicious design may be envisioned to shorten the distance for the remarkable improvement of the power conversion efficiency of the next‐generation photovoltaic cells and suggests a promising application for other NIR photoresponsive devices.     

Synthesis and visible‐light‐derived photocatalysis of titania nanosphere stacking layers prepared by chemical vapor deposition

BACKGROUND: In this study, visible‐light‐derived photocatalytic activity of metal‐doped titanium dioxide nanosphere (TS) stacking layers, prepared by chemical vapor deposition (CVD), was investigated. The as‐grown TS spheres, having an average diameter of 100–300 nm, formed a layer‐by‐layer stacking layer on a glass substrate. The crystalline structures of the TS samples were of anatase‐type. RESULTS: Ultraviolet (UV) absorption confirmed that metallic doping (i.e. Co and Ni) shifted the light absorption of the spheres to the visible‐light region. With increasing dopant density, the optical band gap of the nanospheres became narrower, e.g. the smallest band gap of Co‐doped TS was 2.61 eV. Both Ni‐ and Co‐doped TS catalysts showed a photocatalytic capability in decomposing organic dyes under visible irradiation. In comparison, Co‐doped TiO₂ catalyst not only displays the adsorption capacity, but also the photocatalytic activity higher than the N‐doped TiO₂ catalyst. CONCLUSION: This result can be attributed to the fact that the narrower band gap easily generates electron–hole pairs over the TS catalysts under visible irradiation, thus, leading to the higher photocatalytic activity. Accordingly, this study shed some light on the one‐step efficient CVD approach to synthesize metal‐doped TS catalysts for decomposing dye compounds in aqueous solution. Copyright © 2010 Society of Chemical Industry