Fe(3)O(4)-Ag nanocomposites for optical limiting:broad temporal response and low threshold

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

In situ reduction of Ag on magnetic nanoparticles with gallic acid: effect of the synthesis parameters on morphology

Aim: Synthesis of Fe₃O₄-Ag composite nanoparticles (NPs) by a new in situ reduction of Ag NPs on the surface of Fe₃O₄ NPs using gallic acid as a reducing agent. Materials & methods: The influence of process parameters on NP morphology and functionalization was evaluated by means of field-emission scanning/scanning transmission electron microscopy and Fourier-transform IR spectroscopy. Results & conclusion: The synthesis conditions affected the morphology of the obtained NPs, evidence of the formation of polydispersed aggregates, nanoflower-like or nanodumbbell nanocomposites. In particular, well-defined nanodumbbells were obtained in aqueous media, with an NP/gallic acid ratio of 10:1, while the presence of a silica shell did not improve the morphology of Ag NPs nucleated on the Fe₃O₄ core.

Spatial self-phase modulation of a Gaussian beam transmitted through a ferrofluid

We report on the experimental observation of the diffraction pattern formed in the far-field region when a high-power continuous-wave laser convergent or divergent Gaussian beam passes through a cuvette with ferrofluid. Two different types of diffraction rings with opposite light-intensity distribution are shown in the far field. The difference between the diffractive patterns is attributed to the interaction of the strong spatial self-phase modulation caused by the refractive index change of the medium with wavefront curvature of the input Gaussian beam. The observed behavior of the diffraction pattern dynamics is interpreted theoretically based on the Fresnel-Kirchhoff integral. The negative polarity of nonlinear refraction can be identified by the central interference profiles and the diffraction pattern. At the same time, the self-defocusing phenomena of the ferrofluid can be determined by the type of pattern. The nonlinear refraction coefficients of the ferrofluid were estimated to be ∼-2.89×10^-5cm²/W (convergent Gaussian beam) and ∼-3.53×10^-5cm²/W (divergent Gaussian beam). In addition, the corresponding third-order nonlinear optical susceptibility of the sample was also estimated as ∼1.43×10^-5esu and ∼1.75×10^-5esu, respectively. The experimental results imply a novel potential application of ferrofluid in nonlinear phase modulation devices.

Evolution of Nonlinear Optical Characteristics of Magnetic Nanoparticle Colloidal Suspensions after Laser-Induced Clusters

In this paper, the nonlinear optical properties of magnetic nanoparticle colloidal solutions were studied by the Z-scan technique using 25 ps laser pulses at a wavelength of 1064 nm. Our results reveal that the formed magnetic nanoparticle clusters under high incident laser intensity will greatly affect the nonlinear optical characteristics of the solution. As the intensity of the pulsed laser decreases, the reverse saturable absorption coefficient and nonlinear refractive index of the sample tend to increase. The evolution of this nonlinear characteristic only occurs in liquid suspension. This is confirmed by fixing particles on a substrate upon which the responses observed in the liquid medium are no longer present. Besides, the possibility of generating optical trapping in the focus of the laser pulses is proposed to explain our experimental results.

Fe3O4 nanoparticle-enabled mode-locking in an erbium-doped fiber laser

In this paper, we have proposed and demonstrated the generation of passively mode-locked pulses and dissipative soliton resonance in an erbium-doped fiber laser based on Fe₃O₄ nanoparticles as saturable absorbers. We obtained self-starting mode-locked pulses with fundamental repetition frequency of 7.69 MHz and center wavelength of 1561 nm. The output of a pulsed laser has spectral width of 0.69 nm and pulse duration of 14 ns with rectangular pulse profile at the pump power of 190 mW. As far as we know, this is the firsttimethatFe₃O₄ nanoparticles have been developed as low-dimensional materials for passive mode-locking with rectangular pulse. Our experiments have confirmed that Fe₃O₄ has a wide prospect as a nonlinear photonics device for ultrafast fiber laser applications.

Mode-locked and Q-switched mode-locked fiber laser based on a ferroferric-oxide nanoparticles saturable absorber

We demonstrated an ultrafast erbium-doped fiber laser (EDFL) based on ferroferric-oxide (Fe₃O₄) nanoparticles as a saturable absorber (SA). The investigated SA was based on magnetic fluid deposited on the end face of a fiber ferrule connector. When the SA was inserted into an EDFL cavity, a stable 2.93 ps mode-locked pulse can be achieved by adjusting the intra-cavity polarization controller. The pulse had a central wavelength of 1572.39 nm and a 3 dB bandwidth of 1.39 nm. We also obtained Q-switched mode-locked pulses at 1593.4 nm. The repetition frequency and the temporal width of the Q-switched pulse envelope varied with the pump power. When the pump power reached 225 mW, the maximum average output power and the pulse envelope energy were up to 4.51 mW and 235.5 nJ. To the best of our knowledge, this is the first time that mode-locked and Q-switched mode-locked pulses have been obtained in a fiber laser based on Fe₃O₄ nanoparticles.

Fe3O4 nanoparticles as a saturable absorber for giant chirped pulse generation

Fe₃O₄ nanoparticles (FONPs) are magnetic materials with a small band gap and have well-demonstrated applications in ultrafast photonics, medical science, magnetic detection, and electronics. Very recently, FONPs were proposed as an ideal candidate for pulse generation in fiber-based oscillators. However, the pulses obtained to date are on the order of microseconds, which is too long for real application in communication. Here, we report the use of FONPs synthesized by a sol-hydrothermal method and used as a saturable absorber (SA) to achieve nanosecond pulses in an erbium-doped fiber laser (EDFL) for the first time. The proposed fiber laser is demonstrated to have a narrow spectral width of around 0.8 nm and a fixed fundamental repetition rate (RPR) of 4.63 MHz, whose spectra and pulse dynamics are different from the mode-locked lasers reported previously. It is demonstrated that the proposed fiber laser based on a FONP SA operates in the giant-chirp mode-locked regime. The most important result is the demonstration of a pulse duration of 55 ns at an output power of 16.2 mW, which is the shortest pulse based on FONPs for EDFLs reported to date. Our results demonstrate that the FONP dispersion allows for an excellent photonic material for application in ultrafast photonics devices, photoconductive detectors, and optical modulators.

Broadband polarization-insensitive saturable absorption of Fe2O3 nanoparticles

The synthesis and functionalization of transition-metal oxides are one of the most active research areas in advanced materials. As a typical transition-metal oxide, iron oxide has been widely used in lithium-ion batteries, gas sensors, and for water treatment. Herein, we synthesized Fe₂O₃ nanoparticles by a co-precipitation method that is inexpensive and non-toxic. The Fe₂O₃ nanoparticles exhibited broadband saturable absorption. Furthermore, thin Fe₂O₃ polyvinyl alcohol films were prepared to realize Q-switched operations in a ytterbium-doped fibre laser, an erbium-doped fibre laser, and a thulium-doped fibre laser. Attributed to the polarization-insensitive feature of the saturable absorber, Q-switched cylindrical vector beams were also generated based on mode coupling and selection in two-mode fibre lasers. Such Fe₂O₃ nanoparticles show great promise for use in Q-switching applications of infrared fibre lasers and cylindrical vector lasers.

Thickness-dependent surface plasmon resonance of ITO nanoparticles for ITO/In-Sn bilayer structure

Tuning the localized surface plasmon resonance (LSPR) in doped semiconductor nanoparticles (NPs), which represents an important characteristic in LSPR sensor applications, still remains a challenge. Here, indium tin oxide/indium tin alloy (ITO/In-Sn) bilayer films were deposited by electron beam evaporation and the properties, such as the LSPR and surface morphology, were investigated by UV-VIS-NIR double beam spectrophotometer and atomic force microscopy (AFM), respectively. By simply engineering the thickness of ITO/In-Sn NPs without any microstructure fabrications, the LSPR wavelength of ITO NPs can be tuned by a large amount from 858 to 1758 nm. AFM images show that the strong LSPR of ITO NPs is closely related to the enhanced coupling between ITO and In-Sn NPs. Blue shifts of ITO LSPR from 1256 to 1104 nm are also observed in the as-annealed samples due to the higher free carrier concentration. Meanwhile, we also demonstrated that the ITO LSPR in ITO/In-Sn NPs structures has good sensitivity to the surrounding media and stability after 30 d exposure in air, enabling its application prospects in many biosensing devices.

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the function of optical power limiting. All known mechanisms of optical limiting have been analyzed and discussed for the different types of materials.

Nonlinear optical behaviour of indium-phthalocyanine tethered to magnetite or silica nanoparticles

Enhanced nonlinear optical properties (NLO) were observed for an indium phthalocyanine–magnetite nanocomposite at 532 nm compared to the performance of the bare phthalocyanine and its silica nanoparticle dyad.

Superparamagnetic Ag@Fe3O4 core-shell nanospheres: fabrication, characterization and application as reusable nanocatalysts

Superparamagnetic Ag@Fe(3)O(4) nanospheres with core-shell nanostructures have been prepared by a facile one-pot method. The diameter of the as-synthesized nanospheres was about 200 nm and the core sizes were between 50 and 100 nm. By varying the concentrations, particles with tunable core size and total size are successfully achieved. Time dependent experiments were constructed to investigate the synthesis mechanism, which indicated that the present method corresponded to an Ostwald ripening progress. The BET area of the core-shell nanospheres is about 22.6 m(2)/g and this result indicates that the product shows a porous character. The saturated magnetization of the superparamagnetic Ag@Fe(3)O(4) nanospheres is 27.4 emu g(-1) at room temperature, which enables them to be recycled from the solution by simply applying a small magnet. Due to the unique nanostructure, these particles show high performance in catalytic reduction of 4-nitrophenol and can be used as reusable nanocatalysts.

Nonlinear and magneto-optical transmission studies on magnetic nanofluids of non-interacting metallic nickel nanoparticles

Oxide free stable metallic nanofluids have the potential for various applications such as in thermal management and inkjet printing apart from being a candidate system for fundamental studies. A stable suspension of nickel nanoparticles of ∼ 5 nm size has been realized by a modified two-step synthesis route. Structural characterization by x-ray diffraction and transmission electron microscopy shows that the nanoparticles are metallic and are phase pure. The nanoparticles exhibited superparamagnetic properties. The magneto-optical transmission properties of the nickel nanofluid (Ni-F) were investigated by linear optical dichroism measurements. The magnetic field dependent light transmission studies exhibited a polarization dependent optical absorption, known as optical dichroism, indicating that the nanoparticles suspended in the fluid are non-interacting and superparamagnetic in nature. The nonlinear optical limiting properties of Ni-F under high input optical fluence were then analyzed by an open aperture z-scan technique. The Ni-F exhibits a saturable absorption at moderate laser intensities while effective two-photon absorption is evident at higher intensities. The Ni-F appears to be a unique material for various optical devices such as field modulated gratings and optical switches which can be controlled by an external magnetic field.

The targeted antibacterial and antifungal properties of magnetic nanocomposite of iron oxide and silver nanoparticles

Two types of magnetic binary nanocomposites, Ag@Fe(3)O(4) and γ-Fe(2)O(3)@Ag, were synthesized and characterized and their antibacterial activities were tested. As a magnetic component, Fe(3)O(4) (magnetite) nanoparticles with an average size of about 70 nm and monodisperse γ-Fe(2)O(3) (maghemite) nanoparticles with an average size of 5 nm were used. Nanocomposites were prepared via in situ chemical reduction of silver ions by maltose in the presence of particular magnetic phase and molecules of polyacrylate serving as a spacer among iron oxide and silver nanoparticles. In the case of the Ag@Fe(3)O(4) nanocomposite, silver nanoparticles, caught at the surfaces of Fe(3)O(4) nanocrystals, were around 5 nm in a size. On the contrary, in the case of the γ-Fe(2)O(3)@Ag nanocomposite, ultrafine γ-Fe(2)O(3) nanoparticles surrounded silver nanoparticles ranging in a size between 20 and 40 nm. In addition, the molecules of polyacrylate in this nanocomposite type suppress considerably interparticle magnetic interactions as proved by magnetization measurements. Both synthesized nanocomposites exhibited very significant antibacterial and antifungal activities against ten tested bacterial strains (minimum inhibition concentrations (MIC) from 15.6 mg/L to 125 mg/L) and four candida species (MIC from 1.9 mg/L to 31.3 mg/L). Moreover, acute nanocomposite cytotoxicity against mice embryonal fibroblasts was observed at concentrations of higher than 430 mg/L (Ag@Fe(3)O(4)) and 292 mg/L (γ-Fe(2)O(3)@Ag). With respect to the non-cytotoxic nature of the polyacrylate linker, both kinds of silver nanocomposites are well applicable for a targeted magnetic delivery of silver nanoparticles in medicinal and disinfection applications.