The effect of different substrate temperatures on the structure and luminescence properties of Y2O3:Bi3+ thin films

Y₂O₃:Bi³⁺ phosphor thin films were prepared by pulsed laser deposition in the presence of oxygen (O₂) gas. The microstructure and photoluminescence (PL) of these films were found to be highly dependent on the substrate temperature. X-ray diffraction analysis showed that the Y₂O₃:Bi³⁺ films transformed from amorphous to cubic and monoclinic phases when the substrate temperature was increased up to 600 °C. At the higher substrate temperature of 600 °C, the cubic phase became dominant. The crystallinity of the thin films, therefore, increased with increasing substrate temperatures. Surface morphology results obtained by atomic force microscopy showed a decrease in the surface roughness with an increase in substrate temperature. The increase in the PL intensities was attributed to the crystallinity improvement and surface roughness decrease. The main PL emission peak position of the thin films prepared at substrate temperatures of 450 °C and 600 °C showed a shift to shorter wavelengths of 460 and 480 nm respectively, if compared to the main PL peak position of the powder at 495 nm. The shift was attributed to a different Bi³⁺ ion environment in the monoclinic and cubic phases.     

Bi4Ti3O12 Thin Films from Mixed Bismuth-Titanium Alkoxides

Bi₄Ti₃O₁₂ thin films were obtained by the sol-gel method. The precursor solution was prepared by allowing the two metallic alkoxides, Bi(OC₂H₄OCH₃)₃ and Ti(OC₂H₄OCH₃)₄, to react in 2-methoxy-ethanol to form the mixed alkoxide. This stable sol was deposited by spin-coating onto platinized silicon substrates. X-Ray diffraction patterns indicate that the perovskite initial crystallization temperature is 460°C for powder samples and it ranges between 400 and 500°C, for thin films, as a function of the number of coating layers. Dense, smooth and crack free thin films with grain sizes ranging from 20 nm to 500 nm are obtained, depending on the number of coating layers and on the post-deposition temperature annealing.     

Nanoflower‐Like Bi2WO6 Encapsulated in ORMOSIL as a Novel Photocatalytic Antifouling and Foul‐Release Coating

Herein, the first multi‐purpose antifouling and foul‐release photocatalytic coating based on ORMOSIL thin films doped with nanoflower‐like Bi₂WO₆ is described. Irradiation with visible light of the new films immersed in water produces significant amounts of H₂O₂ by photocatalytic oxidation of water, and allows the degradation of (bio)organic pollutants at the outer surface of the xerogel film.     

Preparation and Properties of Highly Oriented Sr0.3Ba0.7Nb2O6 Thin Films by a Sol-Gel Process

We succeeded in the preparation of epitaxial or highly oriented strontium-barium niobate (Sr_0.3Ba_0.7Nb₂O₆) thin film by a sol-gel process. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)₅ as raw materials, and acetic acid and diethylene glycol monomethyl ether as solvents. Sr_0.3Ba_0.7Nb₂O₆ film sintered at 900°C on MgO(1 0 0) was oriented with c-axis perpendicular to the substrate surface. Sr_0.3Ba_0.7Nb₂O₆ film sintered at 700°C on SrTiO₃(1 0 0) was an epitaxial and oriented with c-axis in parallel to the substrate surface. Transmittance of Sr_0.3Ba_0.7Nb₂O₆ film (film thickness: 144 nm) was more than 60% at the range from 400 to 800 nm. Refractive index was 2.33 at 633 nm. Dielectric constant and dielectric loss of the Sr_0.3Ba_0.7Nb₂O₆ thin films prepared on polycrystal Pt substrates were 600 and 0.06 at room temperature and 1 kHz, respectively. The curie temperature (T_c) of polycrystalline Sr_0.3Ba_0.7Nb₂O₆ thin films was about 200°C. At room temperature and 50 kHz, remanent polarization (P_r) and coercive field (E_c) of the polycrystalline thin films were 1.79 C/cm² and 2.69 kV/cm, respectively.     

Uranium substitution for tungsten in the Bi2WO6–Bi2UO6 system: Formation of a broad high-temperature solid solution

Polythermic studies of Bi₂WO₆–Bi₂UO₆ system revealed existence of a broad Bi₂W_1?xU_xO₆ solid solution with the Aurivillius-type structure. Below 750 °C, the homogeneity area is narrow (x ≤ 0.12) but extends significantly at higher temperatures (up to ca. 75% Bi₂UO₆ at 1025 °C). The solid solution retains orthorhombic symmetry over the entire compositional range, but substitution of U for W results in significant lowering of second harmonic intensity and Curie point suggesting, at high substitution degrees, a very close approach to the archetypic body-centered tetragonal centrosymmetric structure. The known Bi₂WO₆-based solid solutions are discussed in terms of thermal stability, and a general geometrical explanation is suggested. Incorporation of large cations into the B perovskitic positions of [Bi₂O₂][A_n?1B_nO_3n+1] Aurivillius structures seems yet to be restricted by the n = 1 case.     

Synthesis of Thin Bi9O7.5S6 Nanosheets for Improved Photodetection in a Wide Wavelength Range

Bismuth-based compounds possess layered structures with a variety of stacking modes, endowing the compounds with diverse properties. As one type of bismuth oxysulfides, Bi₉O_7.5S₆ nanocrystals has great applications in photodetection; however, the responsivity of bulky Bi₉O_7.5S₆ is limited due to the poor charge separation. Herein, single-crystalline Bi₉O_7.5S₆ thin nanosheets are successfully synthesized by using a solvothermal method. The thickness of the obtained Bi₉O_7.5S₆ nanosheets is down to 15 nm and can be easily tuned by varying the reaction period. Moreover, the Bi₉O_7.5S₆ nanosheets show strong light absorption in the visible and near infrared range, making it a promising candidate in optoelectronics. As a demonstration, the thin Bi₉O_7.5S₆ nanosheets are used as active layer in an optoelectronic device, which exhibits sensitive photoelectric response to light in a wide range of 400–800 nm. The responsivity of the device reaches up to 1140 μA W⁻¹, and the performance of the device is stable after long-period illumination. This work demonstrates a great potential of the thin Bi₉O_7.5S₆ nanosheets in optoelectronic devices, and these nanosheets may also be extended to various optoelectronic applications.     

Optical constants,dispersion energy parameters and dielectric properties of ultra-smooth nanocrystalline BiVO4 thin films prepared by rf-magnetron sputtering

BiVO₄ thin films have been prepared through radio frequency (rf) magnetron sputtering of a pre-fabricated BiVO₄ target on ITO coated glass (ITO-glass) substrate and bare glass substrates. BiVO₄ target material was prepared through solid-state reaction method by heating Bi₂O₃ and V₂O₅ mixture at 800 °C for 8 h. The films were characterized by X-ray diffraction, UV–Vis spectroscopy, LCR meter, field emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. BiVO₄ thin films deposited on the ITO-glass substrate are much smoother compared to the thin films prepared on bare glass substrate. The rms surface roughness calculated from the AFM images comes out to be 0.74 nm and 4.2 nm for the films deposited on the ITO-glass substrate and bare glass substrate for the deposition time 150 min respectively. Optical constants and energy dispersion parameters of these extra-smooth BiVO₄ thin films have been investigated in detail. Dielectric properties of the BiVO₄ thin films on ITO-glass substrate were also investigated. The frequency dependence of dielectric constant of the BiVO₄ thin films has been measured in the frequency range from 20 Hz to 2 MHz. It was found that the dielectric constant increased from 145 to 343 at 20 Hz as the film thickness increased from 90 nm to 145 nm (deposition time increased from 60 min to 150 min). It shows higher dielectric constant compared to the literature value of BiVO₄.     

Crystallographic parameters of Bi2O3 and reduced Graphene-Bi2O3 nano-composite thin film

The Bi₂O₃ and reduced graphene (RG)-Bi₂O₃ nano-composite thin films are synthesized using modified sol-gel process. For structural examination, the samples are analyzed using XRD. Using the Scherrer equation and a modified Scherrer plot, the sample's structural parameters are calculated. The materials' size and strain were estimated from different methods like modified Williamson-Hall (W–H), Halder-Wagner (H–W), and Size Strain Plot (SSP) with logical validity. The different crystallographic parameters obtained are compared and presented in this work.     

Two-step colloidal synthesis of micron-scale Bi2O2Se nanosheets and their electrostatic assembly for thin-film photodetectors with fast response

Recently discovered bismuth oxychalcogenide (Bi₂O₂Se) has aroused great interest due to its ultrahigh carrier mobility, tunable band gap and good environmental stability, making it a promising candidate for high-performance electronics and optoelectronics. Their synthesis by colloidal approaches represents a cost-effective alternative to well-established chemical vapor deposition methods, and the resulting electronic-grade inks are important for large-area printed or wearable electronics. However, it is still challenging to control the colloidal growth of Bi₂O₂Se nanosheets in solution in addition to their assembly into high-performance thin films. Here, we report a two-step colloidal synthesis of Bi₂O₂Se nanosheets by separating the seeding and growth steps, thereby achieving controllable production of nanosheets with a lateral size of 1.4 μm and a thickness of 10 nm at optimized reaction conditions. These Bi₂O₂Se nanosheets are electrostatically assembled into large-area thin films, from which a photodetector is fabricated with a responsivity of 6.1 A/W and a short response time of 368 μs under the 520-nm laser illumination. The device exhibits fast response to modulations as high as 100 kHz, along with a −3 dB bandwidth of 1 kHz. This work provides an important understanding of the controlled colloidal synthesis of Bi₂O₂Se nanosheets, and demonstrates their potential applications in fast photodetectors.     

Tunable and rapid crystallisation of phase pure Bi2MoO6 (koechlinite) and Bi2Mo3O12 via continuous hydrothermal synthesis

Herein, we report the rapid single step hydrothermal synthesis of phase pure Bi₂MoO₆ (koechlinite) and Bi₂Mo₃O₁₂, via a continuous hydrothermal flow synthesis (CHFS) reactor, which uses supercritical water of 375–450 °C at a pressure of 24.1 MPa as a crystallising medium. The product being obtained as highly crystalline nano-materials with high surface area. Simple variation in synthesis condition and appropriate solution stoichiometry were shown to be sufficient to select the phase of the product. The materials synthesised showed significant photcatalytic activity towards the decolourisation of methylene blue in comparison to a commercial gold standard photocatalyst.     

Еlectronic currents in the (+)Bi/Bi2O3/electrolyte system during tensiostatic anodization

The electronic currents in the (+)Bi/Bi₂O₃/electrolyte system have been studied during tensiostatic anodization of Bi in two aqueous and two nonaqueous contact electrolytes. The obtained results are compared with the J _e(E) dependencies, derived from the polarization of already formed Bi₂O₃ films. Furthermore, a discussion based on the theoretical models of Poole–Frenkel, Schottky, and Christov is conducted. Data for relative permittivity of Bi₂O₃ films obtained from tensiostatic anodization are compared with those derived from the polarization of preformed Bi₂O₃ films for the same contact electrolytes.     

The effect of different gas atmospheres on the structure,morphology and photoluminescence properties of pulsed laser deposited Y3(Al,Ga)5O12:Ce3+ nano thin films

Luminescent properties of Y₃(Al,Ga)₅O₁₂:Ce³⁺ phosphor powder and thin films were obtained. The phosphor powder was used as target material for Pulsed Laser Deposition (PLD) of the thin films in the presence of different background gases. Excitation peaks for the powder were obtained at 439, 349, 225 and 189 nm and emission peaks at 512 and 565 nm. X-ray diffraction indicated that better crystallization took place for films deposited in a 20 mTorr O₂ atmosphere. Atomic force microscope revealed an RMS value of 0.7 nm, 2.5 nm and 4.8 nm for the films deposited in vacuum, O₂ and Ar atmospheres, respectively. The highest PL intensity was observed for films deposited in the O₂ atmosphere. A slight shift in the wavelength of the PL spectra was obtained for the thin films due to a change in the crystal field. The thickness of the films varied from 120 nm to 270 nm with films deposited in vacuum having the thin layer and those in Ar having the thick layer. The stoichiometry of the powder was maintained in the film during the deposition as confirmed by Rutherford backscattering spectroscopy.     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.     

Phase formation and thermal stability of the compounds in the Bi2O3-PbO system

The scientific interest for the Bi₂O₃-PbO system has increased due to the importance of the PbO in the high-T _c superconducting phase formation in the Bi₂O₃-SrO-CaO-CuO system. Also Bi₂O₃-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi₂O₃-based solid solutions are well known as high oxygen ion conductors.Previously, several low melting defined compounds have been identified in the system: 6Bi₂O₃·PbO; 3Bi₂O₃·2PbO; 4Bi₂O₃·5PbO; 4Bi₂O₃·6PbO and Bi₂O₃·3PbO.This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi₂O₃/PbO ratio, the compound 6Bi₂O₃·PbO is preferentially formed, followed by the compound 4Bi₂O₃·5PbO. The formation of the compound 4Bi₂O₃·6PbO was not confirmed while the formation of the compound Bi₂O₃ 3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530–780°C.     

Bi2WO6 photocatalytic films fabricated by layer-by-layer technique from Bi2WO6 nanoplates and its spectral selectivity

Bi₂WO₆ multilayer films have been fabricated successfully by a layer-by-layer (LbL) technique from Bi₂WO₆ nanoplates, which show higher visible-light photoactivity (λ>420 nm) than that of Bi₂WO₆ nanoplate powders and P25 TiO₂ films. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and UV-visible absorption spectroscopy. Photocatalytic activities of the films were evaluated by the rhodamine B (RhB) decomposition under UV and visible-light irradiation. Thickness and photoactivity of the film can be modified easily by changing the deposition cycles. Bi₂WO₆ films have the spectral selectivity of the photocatalytic degradation of RhB. Under the wavelength greater than 300 nm, the RhB molecules tend to be transformed to rhodamine over Bi₂WO₆ films selectively. However, in the case of shorter wavelength (λ=254 nm) light irradiation, the RhB molecules can be photodegraded completely.     

Photocatalytic activity of a novel Bi-based oxychloride catalyst Na0.5Bi1.5O2Cl

A Bi-based oxychloride Na_0.5Bi_1.5O₂Cl with a layered structure as a novel efficient photocatalyst was studied in the present paper. The powder was synthesized by a solid state reaction method. It was characterized by X-ray diffraction, scanning electron microscope and UV–vis diffuse reflectance spectrum. Degradation of methyl orange was used to evaluate the photocatalytic activity. The as-synthesized Na_0.5Bi_1.5O₂Cl has a smaller optical band gap of 3.04 eV than BiOCl (E_g = 3.44 eV). It possesses a fair visible-light-response ability. The UV-induced photocatalytic activity follows the decreasing order of BiOCl > Na_0.5Bi_1.5O₂Cl > TiO₂, different from the order of Na_0.5Bi_1.5O₂Cl > TiO₂ > BiOCl under visible light irradiation. The dispersion of Pt over Na_0.5Bi_1.5O₂Cl leads to an obvious increase in the photocatalytic performance. The internal electric fields between [Na_0.5Bi_1.5O₂] and [Cl] slabs favor the efficient separation of photostimulated electron–hole pairs.     

Study of the optimal condition for electroplating of Bi2S3 thin films and their photoelectrochemical characteristics

Bismuth sulfide (Bi₂S₃) thin films were electrodeposited from non-aqueous dimethyl sulfoxide medium containing Bi(NO₃)₃ and thiourea as the precursor salts, triethanol amine as the complexing agent, and TritonX-100 as the surface active agent. The prepared films were subjected to rigorous experimentation in order to validate their potential candidature for solar cells. The films exhibited band gap energy of ∼1.3 eV and resistivity of the order of 2 × 10⁶ Ω cm at room temperature as was obtained from UV–Vis spectroscopy and four-probe measurements, respectively. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive analysis of X-ray were employed to reveal the morphology, structure, and chemical composition of the film matrix. The Bi₂S₃ films were found to be non-decomposable up to the temperature of 1,000 °C with the help of thermogravimetry–differential thermal analysis. The Nyquist and Mott–Schottky plots derived from electrochemical impedance spectroscopy measurements provided important information regarding electrical and semiconducting properties of the films. The n-type film with a donor density of the order of ∼10²³ m⁻³ displayed reasonable photoactivity under illumination and is recommended as a promising candidate for potential photoelectrochemical applications.     

Nonlinear Optical Susceptibility of Fe2O3 Thin Film Synthesized by a Modified Sol-Gel Method

The homogeneous transition metal oxide Fe₂O₃ thin films are synthesized in a modified sol-gel process by spin coating. The third order nonlinear optical susceptibility of the film is about 2 × 10^–9 esu at 488 nm wavelength by the z-scan method with a 180 femtosecond pulse laser beam. The film is expected to be useful for the application of nonlinear optical devices.     

A facile green approach to the synthesis of Bi2WO6@V2O5 heterostructure and their photocatalytic activity evaluation under visible light irradiation for RhB dye removal

Bismuth tungsten oxide and vanadium pentoxide (Bi₂WO₆/V₂O₅) heterostructures are produced by a green synthesis approach using Azadirachta indica extract for photocatalytic performance. The hydrothermal method at temperatures between 120 °C and 140 °C is used to synthesize Bi₂WO₆. Bi₂WO₆ and V₂O₅ phases are formed in pure orthorhombic wells according to the XRD pattern. The SEM displays V₂O₅ nanorods, Bi₂WO₆ hierarchical microspheres that resemble flowers at 120 °C, and particles with a particle-like character at 140 °C. In V₂O₅, the asymmetric stretching vibrations of the triplely coordinated oxygen (chain oxygen) bonds and the vibration of the doubly coordinated oxygen (bridge oxygen) bonds are responsible for a peak at 611 cm^?1. In FTIR spectra between 600 and 1600 cm^?1, the major absorption bands in Bi₂WO₆ are attributed to the W-O stretching, Bi-O stretching, and W-O-W bridging stretching modes. Bi₂WO₆@V₂O₅ at 120 °C has the lowest bandgap energy (2.32 eV) and optical electronegativity (0.62), as well as the highest refractive index (2.57), extinction coefficient (2.21), and dielectric constant (ε_r = 0.72 and ε_i = 11.4) among all samples, making it a suitable material for photocatalysis. Rhodamine blue (RhB) dye degradation is used to measure the photocatalytic activity (PCA) of certain materials. The results showed that heterostructure V₂O₅@Bi₂WO₆ synthesized at 120 °C is more attractive among all samples due to high degradation of RhB dye under sunlight irradiation in 90 min.     

Enhanced photocatalytic properties of Bi2MoO6 nanoplates deposited with intermetallic AgPd nanoparticles by photoreduction method

Bi₂MoO₆ nanoplates modified with intermetallic AgPd nanoparticles synthesized by photoreduction deposition method were used for visible-light-driven photodegradation of rhodamine B. The as-synthesized AgPd/Bi₂MoO₆ nanocomposites were identified by XRD. The 2θ diffraction angle of the (111) plane of pure metallic cubic Ag at 38.11° of heterostructure 10% Ag/Bi₂MoO₆ nanocomposites shifted to a higher diffraction angle at 38.17° of heterostructure 10% Ag_0.7Pd_0.3/Bi₂MoO₆ nanocomposites. TEM images of the as-synthesized nanocomposites showed good metallic Ag and intermetallic AgPd nanoparticles with particle size of 10–12 nm which were fully supported on top of Bi₂MoO₆ nanoplates. Bi₂MoO₆ nanoplates deposited with intermetallic AgPd nanoparticles show significant photocatalytic activity better than Ag/Bi₂MoO₆ and Bi₂MoO₆ due to the formation of AgPd/Bi₂MoO₆ Schottky barrier.