Broad -band nonlinear optical response in Bi2Te0.6S2.4 alloys based on alloy engineering

Alloy engineering plays an important role in regulating the optoelectronic properties of materials. This work demonstrates that Bi2Te0.6S2.4 alloys can extend nonlinear optical response to the near-infrared range. Te alloying at S sites can narrow the band gap, as proved by density functional theory (DFT) calculations, leading to a broadband saturable absorption response ranging from ultraviolet (350 nm) to near-infrared (1100 nm) wavelength with negative nonlinear optical absorption coefficient ranging from -0.12 cm GW-1 to -1.28 cm GW-1. Moreover, the broadband carrier dynamic of Bi2Te0.6S2.4 alloys was investigated via femtosecond transient absorption (TA) at an excitation of 325 nm. A faster carrier dynamic at near-infrared wavelength was observed because of an increase in electron density at the conduction band minimum due to the additional Bi-Te interaction, which was corroborated by DFT calculations. These results suggest that alloy engineering provides an effective way for the development of broadband nonlinear optical devices.

Controlled synthesis of photoresponsive bismuthinite (Bi2S3) nanostructures mediated through a new 1D bismuth-pyrimidylthiolate coordination polymer as a molecular precursor

Bismuthinite (Bi2S3) nanostructures have garnered significant interest due to their appealing photoresponsivity which has positioned them as an attractive choice for energy conversion applications. However, to utilize their full potential, a simple and economically viable method of preparation is highly desirable. Herein, we present the synthesis and characterization including structural elucidation of a new air- and moisture-stable bismuth-pyrimidylthiolate complex. This complex serves as an efficient single-source molecular precursor for the facile preparation of phase-pure Bi2S3 nanostructures. Powder X-ray diffraction (PXRD), Raman spectroscopy, electron dispersive spectroscopy (EDS) and electron microscopy techniques were used to assess the crystal structure, phase purity, elemental composition and morphology of the as-prepared nanostructures. This study also revealed the profound effects of temperature and growth duration on the crystallinity, phase formation and morphology of nanostructures. The optical band gap of the nanostructures was tuned within the range of 1.9-2.3 eV, which is blue shifted with respect to the bulk bandgap and suitable for photovoltaic applications. Liquid junction photo-electrochemical cells fabricated from the as-prepared Bi2S3 nanostructure exhibit efficient photoresponsivity and good photo-stability, which project them as promising candidates for alternative low-cost photon absorber materials.

Enhanced and tunable femtosecond nonlinear optical properties of pure and nickel-doped zinc oxide films

The nonlinear optical properties of pure ZnO and Ni-doped ZnO thin films are explored using the Z-scan technique at different input laser intensities and an excitation wavelength of 750 nm by 100 fs laser pulses. The pure ZnO and Ni-doped ZnO thin films were prepared by radio frequency magnetron sputtering at room temperature. A scanning electron microscope equipped with energy-dispersive x-ray spectroscopy was used to measure the thickness and composition of the thin films, while a UV-visible spectrophotometer was used to measure the linear optical properties. The structure of the thin films was measured using x-ray diffraction. Saturable absorption (SA) was observed in the pure ZnO thin film, while Ni-doped ZnO illustrated a combination of SA and reverse SA (RSA). The nonlinear absorption coefficient (β) and nonlinear refractive index (n₂) of both pure ZnO and Ni-doped ZnO thin films were found to be input laser intensity dependent. As the input laser intensity increased, the nonlinear absorption coefficient and the nonlinear refractive index of both samples increased. An enhancement of two times in the nonlinear refractive index was observed for the Ni-doped ZnO thin film compared to the pure ZnO thin film. The optical limiting behavior of pure ZnO and Ni-doped ZnO thin films was investigated, and the data demonstrated that Ni-doped ZnO thin film is a good candidate for optical limiter applications due to the presence of strong RSA.

Layer-Dependent Nonlinear Optical Properties of WS2, MoS2, and Bi2S3 Films Synthesized by Chemical Vapor Deposition

Two-dimensional (2D) layered materials have shown layer-dependent optical properties in both linear optical and nonlinear optical (NLO) regimes due to prominent interlayer coupling and quantum confinement in an atomic scale. However, the NLO properties become more complicated as both saturable absorption (SA) and reverse saturable absorption (RSA) easily happen in 2D materials, which results in a significant challenge to understand the evolution of nonlinear absorption with layers. Motivated by this, chemical vapor-deposited chalcogenide compounds (WS₂, MoS₂, and Bi₂S₃) are used to investigate the pump intensity and layer number-dependent NLO properties. The values of nonlinear absorption coefficients of these chalcogenide compounds increase with the pump intensity by an 800 nm femtosecond laser, which can be described by an empirical power law function. The SA process due to the large transition probability of the ground state readily takes place in thick samples, while RSA occurs easily in thin samples due to the two-photon absorption (TPA). The transition from TPA to SA is deduced to occur at 13L-WS₂, 15L-MoS₂, and 5L-Bi₂S₃, which is related to the layer-dependent band gaps. Our results provide an efficient way to tune optical nonlinearities with a controlled layer number and to design corresponding NLO devices such as optical switches and saturable absorbers.

Ultra-low thermal conductivity in Na/Sb chalcobismuthates: synthesis, crystal structures, optical properties and23Na NMR spectroscopy

The synthesis and characterization of mixed metal phases, Na₂BiSbQ₄(Q = S, Se, Te), containing only one metal site in the unit cell, which resulted in extremely low thermal conductivities.

Green synthesis of bismuth sulfide nanostructures with tunable morphologies and robust photoelectrochemical performance

Green synthesis of tunable Bi₂S₃ nanomaterials with tailored photoelectrochemical performance was proposed in aqueous medium without any organic reagents.

AuAg@CdS double-walled nanotubes: synthesis and nonlinear absorption properties

Novel AuAg@CdS double-walled nanotubes (DWNTs) were successfully fabricated through a three-step solvothermal method, starting with silver nanowires as the template. In the DWNTs, a uniform layer of a CdS shell is coated onto the AuAg nanotubes, finally forming the one-dimensional nanocomposites. Nonlinear optical analysis indicated that the plasmon-exciton interaction in the AuAg@CdS DWNTs induced an obviously saturated absorption response under visible light excitation, in contrast to individual AuAg nanotubes and CdS shells. Furthermore, the effective nonlinear absorption coefficient of the AuAg@CdS DWNTs was 7 times larger than that of the CdS shell, which was attributed to the local field enhancement effect. Such a unique morphological configuration and optical properties make AuAg@CdS DWNTs an ideal candidate for next generation nano-photonic devices employed as a mode-locking element, optical switch, and so on.

In-Situ Hydrothermal Synthesis of Bi-Bi2O2CO3 Heterojunction Photocatalyst with Enhanced Visible Light Photocatalytic Activity

Bismuth containing nanomaterials recently received increasing attention with respect to environmental applications because of their low cost, high stability and nontoxicity. In this work, Bi-Bi₂O₂CO₃ heterojunctions were fabricated by in-situ decoration of Bi nanoparticles on Bi₂O₂CO₃ nanosheets via a simple hydrothermal synthesis approach. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were used to confirm the morphology of the nanosheet-like heterostructure of the Bi-Bi₂O₂CO₃ composite. Detailed ultrafast electronic spectroscopy reveals that the in-situ decoration of Bi nanoparticles on Bi₂O₂CO₃ nanosheets exhibit a dramatically enhanced electron-hole pair separation rate, which results in an extraordinarily high photocatalytic activity for the degradation of a model organic dye, methylene blue (MB) under visible light illumination. Cycling experiments revealed a good photochemical stability of the Bi-Bi₂O₂CO₃ heterojunction under repeated irradiation. Photocurrent measurements further indicated that the heterojunction incredibly enhanced the charge generation and suppressed the charge recombination of photogenerated electron-hole pairs.

Synthesis of Bi2S3-Au Dumbbell Heteronanostructures with Enhanced Photocatalytic and Photoresponse Properties

In this article, novel types of Bi₂S₃-Au heterostructures are fabricated through rationally controlling the growth atmosphere. Under argon, Au nanoparticles are preferentially deposited onto the tips of Bi₂S₃ nanorods to form Bi₂S₃-Au dumbbell heterostructures. In contrast, because of the etching effect by amine, Au nanoparticles are randomly anchored onto the surface of nanorods to form Bi₂S₃-Au nanocorns in the presence of oxygen. Furthermore, the size of gold nanoparticles can be controlled through adjusting the concentration of reaction precursors. Bi₂S₃-Au dumbbells show superior activity for the photodegradation of organic pollutants and an enhanced photoresponse compared to the Bi₂S₃-Au nanocorns. The significantly improved photocatalytic performance of Bi₂S₃-Au dumbbells is ascribed to the more efficient charge separation compared to that of Bi₂S₃-Au nanocorns. These heterostructures composed of environmentally friendly elements are expected to be promising for applications in the field of clean energy.

Insights into the binding of photothermal therapeutic agent bismuth sulfide nanorods with human serum albumin

The interaction of microwave synthesized bismuth sulfide nanorods with human serum albumin was investigated using multispectroscopic techniques such as absorption spectroscopy, fluorescence spectroscopy and circular dichroism spectroscopy.

Taking bismuthinite to bismuth sulfide nanorods in two easy steps

Treatment of bismuthinite with aryldithioc acids under sonication leads easily to the formation and isolation of bismuth(iii) aryldithioate complexes [Bi(S₂CAr)₃] which decompose readily to give well formed Bi₂S₃ nanorods.

Single-crystalline Bi19Br3S27 nanorods with an efficiently improved photocatalytic activity

Single-crystalline Bi₁₉Br₃S₂₇ nanorods were prepared and showed excellent visible-light photocatalytic performance.

Soft template mediated synthesis of Bi–In–Zn–S and its efficient visible-light-driven decomposition of methylene blue

Bi–In–Zn–S nanostructures were successfully synthesized in PEG-PPG-PEG at various temperatures and are used as recyclable photocatalysts for the degradation of methylene blue under visible light (sunlight and 200 W tungsten lamp).