Metastable γ-Bi2O3 tetrahedra: Phase-transition dominated by polyethylene glycol, photoluminescence and implications for internal structure by etch

Epitaxial Growth of 2D Ultrathin Metastable γ-Bi2 O3 Flakes for High Performance Ultraviolet Photodetection

Ultraviolet detection is of great significance due to its wide applications in the missile tracking, flame detecting, pollution monitoring, and so on. The nonlayered semiconductor γ-Bi₂ O₃ is a promising candidate toward high-performance UV detection due to the wide bandgap, excellent light sensitivity, environmental stability, nontoxic and elemental abundance properties. However, controllable preparation of ultrathin 2D γ-Bi₂ O₃ flakes remains a challenge, owing to its nonlayered structure, metastable nature, and other competing phases. Moreover, the UV photodetectors based on 2D γ-Bi₂ O₃ flake have not been implemented yet. Here, ultrathin (down to 4.8 nm) 2D γ-Bi₂ O₃ flakes with high crystal quality are obtained via a van der Waals epitaxy method. The as-synthesized single-crystalline γ-Bi₂ O₃ flakes show a body-centered cubic structure and grown along (111) lattice plane as revealed by experimental observations. More importantly, photodetectors based on the as-synthesized 2D γ-Bi₂ O₃ flakes exhibit promising UV detection ability, including a responsivity of 64.5 A W^-1 , a detectivity of 1.3 × 10¹³ Jones, and an ultrafast response speed (τ_rise  ≈ 290 µs and τ_decay  ≈ 870 µs) at 365 nm, suggesting its great potential for various optoelectronic applications.

Phase transformation and room temperature stabilization of various Bi2O3 nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species

We report the grain growth from the nanoscale to microscale and a transformation sequence from Bi →β-Bi₂O₃→γ-Bi₂O₃→α-Bi₂O₃ with the increase of annealing temperature. The room temperature (RT) stabilization of β-Bi₂O₃ nanoparticles (NPs) was attributed to the effect of reduced surface energy due to adsorbed carbon species, and oxygen vacancy defects may have played a significant role in the RT stabilization of γ-Bi₂O₃ NPs. An enhanced red emission band was evident from all the samples attributed to oxygen-vacancy defects formed during the growth process in contrast with the observed white emission band from the air annealed Bi ingots. Based on our experimental findings, the air annealing induced oxidation of Bi NPs and transformation mechanism within various Bi₂O₃ nano-polymorphs are presented. The outcome of this study suggests that oxygen vacancy defects at the nanoscale play a significant role in both structural stabilization and phase transformation within various Bi₂O₃ nano-polymorphs, which is significant from theoretical consideration.

Bi2O3-BiFeO3 Glass-Ceramic: Controllable β-/γ-Bi2O3 Transformation and Application as Magnetic Solar-Driven Photocatalyst for Water Decontamination

Glass and glass-ceramic materials containing photoactive and magnetic crystalline phases were prepared from Fe₂O₃ and Bi₂O₃ using the conventional melt method. All samples were characterized in terms of formed phases, morphological analyses, optical properties, and magnetic properties. Formation of the photoactive tetragonal β- and body-centered cubic γ-Bi₂O₃ phases along with the magnetic BiFeO₃ and Fe₃O₄ phases was revealed. However, the crystalline structure relied on the composition and the applied heat-treatment time. β-/γ-Bi₂O₃ transformation could be controlled by the heat-treatment time. The samples exhibited variable magnetic properties depending on their composition. All of the samples showed excellent absorbance in visible light with an optical band gap of 1.90-2.22 eV, making them ideal for solar-light-driven photocatalysis. The best performance was recorded for the sample containing equal amounts of Fe₂O₃ and Bi₂O₃ due to the formation of γ-Bi₂O₃/BiFeO₃ heterojunction in this sample.

Structural and Enhanced Optical Properties of Stabilized γ‒Bi2O3 Nanoparticles: Effect of Oxygen Ion Vacancies

We report the synthesis of room temperature (RT) stabilized γ–Bi₂O₃ nanoparticles (NPs) at the expense of metallic Bi NPs through annealing in an ambient atmosphere. RT stability of the metastable γ–Bi₂O₃ NPs is confirmed using synchrotron radiation powder X-ray diffraction and Raman spectroscopy. γ–Bi₂O₃ NPs exhibited a strong red-band emission peaking at ~701 nm, covering 81% integrated intensity of photoluminescence spectra. Our findings suggest that the RT stabilization and enhanced red-band emission of γ‒Bi₂O₃ is mediated by excess oxygen ion vacancies generated at the octahedral O(2) sites during the annealing process.

γ-Bi2O3 - To Be or Not To Be? Comparison of the Sillenite γ-Bi2O3 and Isomorphous Sillenite-Type Bi12SiO20

The "controlled" synthesis of metastable γ-Bi₂O₃ by solution based approaches was reported several times recently, but the formation of Bi₁₂SiO₂₀ in the presence of trace amounts of silicates renders the results to be questionable. Here, the preparation of the Sillenite γ-Bi₂O₃ and the Sillenite-type Bi₁₂SiO₂₀ starting from the polynuclear bismuth oxido cluster [Bi₃₈O₄₅(O₂CC₃H₅)₂₄(DMSO)₉] is reported. γ-Bi₂O₃ crystallizes after calcination at 800 °C of the silicate-free hydrolysis product "[Bi₃₈O₄₅(OH)₂₄]" on a silver sheet. Corrosion of the substrate causes contamination with silver, which is not incorporated into the Bi-O lattice, and was removed by treatment with an aqueous KCN-solution. Bi₁₂SiO₂₀ was obtained after hydrothermal treatment of the bismuth oxido cluster in the presence of NaOH in glass vessels or Na₂SiO₃ in a Teflon-lined reactor vessel followed by calcination at 600 °C. PXRD studies, scanning electron microscopy, nitrogen adsorption measurements, IR- and Raman spectroscopy, diffuse UV-vis spectroscopy, and DSC were used for characterization. The phase transition of γ-Bi₂O₃ to give α-Bi₂O₃ occurred slowly in the temperature range of 348-510 °C ( Δ H_γ→α = 6.57 kJ·mol^-1). The silver-containing γ-Bi₂O₃ exhibits slightly increased Raman modes compared to the silver-free sample due to the SERS effect. In the diffuse UV-vis spectrum γ-Bi₂O₃ exhibits an absorption edge at λ = 485 nm ( E _g = 2.76 eV), and the contamination with silver results in an additional absorption edge at λ = 572 nm. Silver-free γ-Bi₂O₃ exhibits an absorption edge at λ = 460 nm ( E _g = 2.83 eV) and Bi₁₂SiO₂₀ at λ = 422 nm ( E _g = 3.16 eV). The photocatalytic activity of the compounds was investigated in the decomposition of aqueous rhodamine B under visible light irradiation, showing silver-containing γ-Bi₂O₃ to be slightly more effective compared to Bi₁₂SiO₂₀ and significantly more effective than the silver-free γ-Bi₂O₃.

Investigations on the growth of bismuth oxido clusters and the nucleation to give metastable bismuth oxide modifications

Investigations on bismuth oxido clusters are focused on the nucleation and growth processes towards large cluster motifs and their stability in the gas phase, which has been studied by electrospray ionization mass spectrometry (ESI-MS), molecular dynamics (MD) simulations and X-ray scattering experiments evaluated by pair distribution function (PDF) analysis. The formation of metastable bismuth(III) oxides was obtained by hydrolysis of polynuclear bismuth oxido clusters and subsequent thermal treatment under non-equilibrium conditions. Temperature dependent PXRD and Raman spectroscopic experiments gave insight into the formation process of metastable β-Bi

Controlled synthesis of bismuth-containing compounds (α-, β- and δ-Bi2O3, Bi5O7NO3 and Bi6O6(OH)2(NO3)4·2H2O) and their photocatalytic performance

A series of bismuth-containing compounds including α-, β- and δ-Bi₂O₃, Bi₅O₇NO₃ and Bi₆O₆(OH)₂(NO₃)₄·2H₂O could be easily prepared by varying the base and solvent.