Raman scattering in monocrystal Bi3B5O12

Raman spectra of a Bi₃B₅O₁₂ monocrystal are investigated for the first time and compared with the Raman spectra of crystals α-Bi₂O₃ and Bi₁₂SiO₂₀. The most intensive lines observed in the Raman spectrum of Bi₃B₅O₁₂ are identified. Promising prospects of use of Bi₃B₅O₁₂ crystals as SRS converters of radiation are shown.     

Heat capacity of oxides in the Bi2O3-SiO2 system

The high-temperature heat capacity of Bi₄Si₃O₁₂, Bi₂SiO₅, and Bi₁₂SiO₂₀ has been investigated. It has been found that there is a correlation between the specific heat C _p ⁰ (298 K) and the composition of oxides in the Bi₂O₃-SiO₂ system.     

Study of glasses and glass ceramics in Bi2O3-GeO2-Fe2O3 and Bi2O3-GeO2-Cr2O3 systems by optical spectroscopy

The ferroelectric Bi₂GeO₅ crystalline phase is synthesized by heat treatment of 1Bi₂O₃-1GeO₂-xFe₂O₃ and 1Bi₂O₃-1GeO₂-yCr₂O₃ glasses. The obtained glass ceramics and initial glasses are studied using X-ray diffraction analysis and optical spectroscopy. The dielectric characteristics are measured, and the Curie temperature is determined. The effect of chromium and iron ions on the absorption spectra and dielectric properties of glasses and glass ceramics is determined.     

Solid-state synthesis of Bi2O3/BaTiO3 heterostructure: preparation and photocatalytic degradation of methyl orange

In this work, Bi₂O₃/BaTiO₃ heterostructure were prepared through a solid milling and annealing process. It was found that Bi³⁺ dissolved in the BaTiO₃ lattice and the chemical bond was constructed between the interface of Bi₂O₃ and BaTiO₃ after annealing process. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-visible absorption spectra were used to characterize the Bi₂O₃/BaTiO₃ heterostructure. Furthermore, UV-induced catalytic activities of the Bi₂O₃/BaTiO₃ heterostructure was studied by a degradation reaction of methyl orange (MO) dye. The band gap of the Bi₂O₃/BaTiO₃ heterostructure was estimated to be 3.0 eV. Compared with pure Bi₂O₃ powders, the Bi₂O₃/BaTiO₃ heterostructure had a much higher catalytic activity. An excellent performance of the photocatalytic property of the Bi₂O₃/BaTiO₃ heterostructure is ascribed to high mobility of species and effective separation of photogenerated carriers driven by the photoinduced potential difference generated at the Bi₂O₃/BaTiO₃ junction interface, demonstrating that the Bi₂O₃/BaTiO₃ heterostructure is a promising candidate as a photocatalyst.     

Effect of excess Bi2O3 on the electrical properties and microstructure of (Bi1/2Na1/2)TiO3 ceramics

(Bi_1/2Na_1/2)TiO₃ ceramics (BNT) with 0–6 mol% of excess Bi₂O₃ are prepared by conventional solid-state sintering. The electrical properties of the samples are examined. The addition of excess Bi₂O₃ reduces the leakage current of BNT ceramics significantly, thus facilitating the poling process, and improves their piezoelectric properties slightly for certain amounts of added Bi₂O₃. BNT ceramics have very high dielectric constants and dissipation factors at low frequency and high temperature due to their high conductivity. Adding excess Bi₂O₃ to BNT ceramics affects their dielectric behavior and phase transition temperatures. Grain growth is suppressed by adding Bi₂O₃ and no second phase is observed for BNT ceramics with up to 6 mol% of excess Bi₂O₃ added.     

Ferroelectric characteristics of silicate-bound Bi4Ti3O12 thin films

40-nm-thick Bi₄Ti₃O₁₂ films have been deposited by spin coating with a hybrid precursor solution of bismuth-2-ethylhexanoate, titanium tetraisopropoxide and tetraethysilicate. The 500 °C-annealed thin film consists of Bi₄Ti₃O₁₂ grains bound by ultra-thin amorphous silicate layers. The film shows a high degree of crystallinity with random orientation and exhibits a structure-dependent propeller-like P–V hysteresis loop. The ultra-thin layer of amorphous silicate is found to have multiple functions of binder, compositional buffer and insulator, which results in an improvement of the electrical properties of the Bi₄Ti₃O₁₂-Bi₂O₃×SiO₂ thin films. PACS 77.84.-s; 68.37.-d; 81.15.-z     

A facile preparation strategy for hollow-structured Bi2O3/Bi2WO6 heterojunction with high visible light photocatalytic activity

A hollow-structured heterojunction consisting of Bi₂WO₆ nanoplatelets and Bi₂O₃ nanoparticles was successfully prepared by a facile solvothermal process. Bi₂O₃/Bi₂WO₆ heterojunction is the aggregate of some hollow spheres with diameter ranging from several hundred nanometers to 1.5 μm and is connected to each other by tube-like cavums. On the basis of scanning and transmission electron microscopy observation and X-ray diffraction analysis of the samples synthesized at different reaction stages, a possible growth mechanism was proposed for the growth of hollow-structured Bi₂O₃/Bi₂WO₆ heterojunction. Its photocatalytic activity was evaluated by degradation of rhodamine B under visible-light irradiation (λ>400 nm). The results indicate that the hollow-structured Bi₂O₃/Bi₂WO₆ heterojunction exhibits much higher photocatalytic activity than both pure Bi₂WO₆ and pure Bi₂O₃. The improved photocatalytic performance can be ascribed to the heterojunction of Bi₂O₃ and Bi₂WO₆ in the framework in which the hierarchical hollow structure possesses good permeability and large surface area. More importantly, the hollow-structured Bi₂O₃/Bi₂WO₆ heterojunction is not only highly stable but also easy to be separated by simple sedimentation for recycle.     

Photoluminescence characteristics and energy transfer between Bi3+ and Eu3+ in Gd2O3: Eu3+, Bi3+ nanophosphors

Bi³⁺ and Eu³⁺ codoped cubic Gd₂O₃ nanocrystals were prepared by the Pechini sol-gel method. Their photoluminescent properties were investigated under ultraviolet light excitation. The introduction of Bi³⁺ ions broadened the excitation band of Eu³⁺ emission, of which a new strong band occurred ranging from 320 to 380 nm due to the 6s²→6s6p transition of Bi³⁺ ions, implying a very efficient energy transfer from Bi³⁺ ions to Eu³⁺ ions. Upon 325 and 355 nm light excitation, the luminescent intensity of Eu³⁺ ions was remarkably improved by the incorporation of Bi³⁺ ions. But a significant quenching of Eu³⁺ emission was observed under 266 nm light excitation when Bi³⁺ was codoped. The possible energy transfer processes between Bi³⁺ and Eu³⁺ were discussed. The decay curves of Eu³⁺ emission under the excitation of 266 nm pulsed laser were measured and gave further evidence for our discussion.     

Broadband infrared luminescence in Yb-doped Bi2O3–GeO2 glasses

The Yb-doped Bi₂O₃–GeO₂ glasses were prepared by the conventional melt quenching technique. Near-infrared (NIR) broadband emission was found at about 1024 nm, and 1330 nm (under 785 nm excitation), and the measured fluorescent lifetime was about several hundred microseconds. The emission intensity of Yb-doped Bi₂O₃–GeO₂ glasses increased with increasing of Yb dopant in our experiments. The NIR emission should be related to Yb³⁺ and lower valence Bi ions.     

UV-visible and infrared absorption spectra of Bi2O3 in lithium phosphate glasses and effect of gamma irradiation

Ultraviolet and visible absorption spectra of prepared undoped lithium phosphate glass and samples of the same nominal composition with additional Bi₂O₃ contents were measured before and after being subjected to gamma doses of 3 and 6 Mrad. The base undoped lithium phosphate glass exhibits strong charge transfer ultraviolet absorption bands, which are related to unavoidable presence of trace iron impurities within the raw materials for the preparation of this glass. Bi₂O₃-containing glasses show the extension of UV absorption beside the resolution of visible bands at 400, 450, and 700 nm with the increase of Bi₂O₃ content due the sharing of absorption of Bi³⁺ ions. Gamma irradiation of the base glass reveals extended induced bands; the UV bands are related to the conversion of some Fe²⁺ to Fe³⁺ through photochemical reactions during the irradiation process. The visible induced bands are related to the formation of positive hole centers from the host phosphate glass. Glasses containing Bi₂O₃ are observed to show some shielding behavior, which is attributed to the presence of heavy weight and large atomic number of Bi³⁺ ions. Infrared absorption spectral measurements of the base lithium phosphate glass show characteristic vibrational modes which are related to specific phosphate groups. The addition of Bi₂O₃ in measurable percent produces additional vibrational bands due to the introduction of Bi–O groups such as BiO₃ and BiO₆.     

Magnetic and transport properties of electron-doped Ca3−x Bi x Mn2O7

Ca_3?x Bi _x Mn₂O₇ with the nominal composition x=0.05, 0.1, 0.2 and 0.3 is synthesized by solid-state reaction. The refined X-ray diffraction pattern of Ca_2.807Bi_0.193Mn₂O₇ with the nominal Bi³⁺ content x=0.2 indicates that about 71 % of the Bi³⁺ ion enters into the Ca²⁺ (2a) site and the remaining 29 % is in the Ca²⁺ (4e) site. The doped Bi³⁺ ion produces a ferromagnetic component in the antiferromagnetic matrix. Below the transition temperature, at about 110 K, the ferromagnetic and antiferromagnetic interactions coexist. The alignment of the magnetic moment is canted at 5 K. The electric transport shows insulating behavior. Around the magnetic transition, at about 110 K, the resistance sharply drops like a well. A model proposed by Glazman and Matveev (GM model) is applied to the thermal variation of the resistance from 40 K to 138 K. Above this temperature, it is due to thermally activated hopping of small polarons with the activation energy of 50 meV. A negative magnetoresistance, 17 %, is observed with the doping content as low as 0.05. The magnetoresistance is due to the spin-polarized inelastic tunneling through nonmagnetic localized states embedded in an insulating barrier.     

g-C3N4 modified Bi2O3 composites with enhanced visible-light photocatalytic activity

Novel g-C₃N₄ modified Bi₂O₃ (g-C₃N₄/Bi₂O₃) composites were synthesized by a mixing-calcination method. The samples were characterized by thermogravimetry (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and photocurrent-time measurement (PT). The photocatalytic activity of the composites was evaluated by degradation of Rhodamine B (RHB) and 4-chlorophenol (4-CP) under visible light irradiation (>400 nm). The results indicated that the g-C₃N₄/Bi₂O₃ composites showed higher photocatalytic activity than that of Bi₂O₃ and g-C₃N₄. The enhanced photocatalytic activity of the g-C₃N₄/Bi₂O₃ composites could be attributed to the suitable band positions between g-C₃N₄ and Bi₂O₃. This leads to a low recombination between the photogenerated electron–hole pairs. The proposed mechanism for the enhanced visible-light photocatalytic activity of g-C₃N₄/Bi₂O₃ composites was proven by PL and PT analysis.     

Dielectric polarization of bismuth titanate,Bi2O3·3TiO2

Experimental data describing the dielectric polarization of polycrystalline bismuth titanate, Bi₂O₃·3TiO₂, is cited, and the physical nature of its polarization discussed. We conclude that Bi₂O₃·3TiO₂ at temperatures equal to or lower than that of liquid nitrogen is a ferroelectric, while at considerably higher temperatures it is a normal relaxation process dielectric.     

Epitaxial films (Bi,Gd)3(Ga,Pt)2Ga3O12 grown by liquid-phase epitaxy

Single-crystal films of complex composition (Bi,Gd)₃(Ga,Pt)₂Ga₃O₁₂ on Gd₃Ga₅O₁₂(111) substrates are synthesized by liquid-phase epitaxy from a supercooled solution-melt based on Bi₂O₃-B₂O₃ flux. Optical absorption of Bi³⁺ and Pt³⁺ ions in these films is investigated in the wavelength range from 200 to 860 nm.     

Micro‐Raman study of exfoliated Bi2Sr2CaCu2O8+δ single crystals with different thicknesses

Exfoliated Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) single crystals were prepared by micromechanical cleavage of bulk Bi‐2212 single crystals on SiO₂/Si substrates. Room temperature micro‐Raman spectra were collected using a 532‐nm laser source. The evolutions of the spectra of A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) Raman modes with different thicknesses of the samples were studied. The refractive index of Bi‐2212 single crystal was obtained by studying the intensity evolutions based on the interference effect. The observed wavenumber shifts of the A_1g (Bi), A_1g (Sr), and A_1g (O_Bi) modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis, characterization, thermo- and photoluminescence properties of Bi3+ co-doped Gd2O3:Eu3+ nanophosphors

Gd₂O₃:Eu³⁺ (4 mol%) co-doped with Bi³⁺ (Bi = 0, 1, 3, 5, 7, 9 and 11 mol%) ions were synthesized by a low-temperature solution combustion method. The powders were calcined at 800°C and were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier transform infrared and UV–Vis spectroscopy. The PXRD profiles confirm that the calcined products were in monoclinic with little cubic phases. The particle sizes were estimated using Scherrer’s method and Williamson–Hall plots and are found to be in the ranges 40–60 nm and 30–80 nm, respectively. The results are in good agreement with TEM results. The photoluminescence spectra of the synthesized phosphors excited with 230 nm show emission peaks at ～590, 612 and 625 nm, which are due to the transitions ⁵D₀→⁷F₀, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₃ of Eu³⁺, respectively. It is observed that a significant quenching of Eu³⁺ emission was observed under 230 nm excitation when Bi³⁺ was co-doped. On the other hand, upon 350 nm excitation, the luminescent intensity of Eu³⁺ ions was enhanced by incorporation of Bi³⁺ (5 mol%) ions. The introduction of Bi³⁺ ions broadened the excitation band of Eu³⁺ of which a new strong band occurred ranging from 320 to 380 nm. This has been attributed to the 6s²→6s6p transition of Bi³⁺ ions, implying a very efficient energy transfer from Bi³⁺ ions to Eu³⁺ ions. The gamma radiation response of Gd₂O₃:Eu³⁺ exhibited a dosimetrically useful glow peak at 380°C. Using thermoluminescence glow peaks, the trap parameters have been evaluated and discussed. The observed emission characteristics and energy transfer indicate that Gd₂O₃:Eu³⁺, Bi³⁺ phosphors have promising applications in solid-state lighting.     

Luminescence centers in Pb2Bi6O11 and Sn2Bi6O11 ceramics

We have studied the luminescence spectra and luminescence excitation spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics at 80 K. We have used the Alentsev-Fock to decompose the spectra into elementary components. We have established that the luminescence spectra of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ ceramics contain three elementary bands each with maxima at 2.60, 2.32, 12.93 eV and 2.62, 2.30, 2.00 eV. Comparison of the data obtained with the results of a study of the luminescence spectra for a series of bismuth-containing oxide compounds suggest that luminescence of Pb₂Bi₆O₁₁ and Sn₂Bi₆O₁₁ is due to radiative processes in structural complexes containing a bismuth ion in a nearest-neighbor oxygen environment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 597–600, September–October, 2006.     

Enhancement of up-conversion luminescence in Zn2SiO4:Yb3+, Er3+ by co-doping with Li+ or Bi3+

Yb³⁺/Er³⁺ co-doped Zn₂SiO₄ ceramics are rapidly synthesized by the microwave radiation method. Green and red up-conversion emissions are observed in Zn₂SiO₄: Yb³⁺, Er³⁺ ceramics under 980 nm excitation. The influence of co-doped Li⁺ or Bi³⁺ ion on luminescence intensity for the phosphors has been investigated. At Li⁺ or Bi³⁺ doping concentration of 1 mol%, up-converted green emission can be increased by 6 times and 20 times, respectively. It is believed that co-doped Li⁺ or Bi³⁺ ion results in the local distortion of Er³⁺ in Zn₂SiO₄, increasing the intra-4f transitions of Er³⁺ ions. The local distortion is proved by spectral probing method with Eu³⁺.     

Structural and electric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(100) substrates under an oxygen pressure of 10 Pa by pulsed laser deposition. The substrate temperature varied from 500 ^°C to 750 ^°C. Effects of substrate temperature on the crystallinity, microstructure, and electric properties of Bi₂Zn_2/3Nb_4/3O₇ thin films have been systematically investigated. Bi₂Zn_2/3Nb_4/3O₇ thin films are amorphous in nature at a substrate temperature of 500 ^°C. With increase of substrate temperature to 550 ^°C, thin films begin to crystallize. At higher temperature of 750 ^°C, Bi₂O₃ phase can be detected in thin films. However, the crystallized thin films exhibit a cubic pyrochlore structure, not a monoclinic zirconolite structure, which is probably attributed by the composition deviation from the stoichiometric ratio. The resultant Bi₂Zn_2/3Nb_4/3O₇ thin films exhibit the character with high dielectric constant and low loss tangent. The dielectric constant gradually increases with the substrate temperature and reaches a maximum at 700 ^°C. The dielectric constant and loss tangent of the thin films deposited at 700 ^°C are 152 and 0.002 at 10 kHz, respectively. With further increase of substrate temperature to 750 ^°C, the dielectric constant decreases to 128. However, the tunability of the resultant thin films disappears, and the temperature coefficients are positive, which implies a more ordered structure in thin films.     

Growth of Bi2O3 rods using a trimethylbismuth and oxygen mixture

We have successfully grown the rod-like structures of bismuth oxide (Bi₂O₃) on silicon substrate by a reaction of a trimethylbismuth (TMBi) and oxygen (O₂) mixture without using any catalyst. We have characterized the samples by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The products consisted of bundles of rod-like structures. The Bi₂O₃ rods were of monoclinic structure. PACS 81.07.-b; 81.15.Gh