基于表面等离子体共振效应的Ag(Au)/半导体纳米复合光催化剂的研究进展

由具有表面等离子体共振(surface plasmon resonance,SPR)效应的贵金属(Ag、Au等)纳米粒子和半导体纳米结构组成的纳米复合光催化剂具有优异的可见光光催化活性,成为新型光催化材料的研究热点之一。本文综述了Ag(Au)/半导体纳米复合光催化剂的制备方法、基本性质以及光催化应用方面的一些重要研究进展;重点介绍了Ag(Au)等纳米粒子的表面等离子共振增强可见光催化活性的机理,以及Ag(Au)纳米粒子与不同类型半导体复合的光催化剂的光催化性能,其中所涉及的半导体包括金属氧化物、硫化物和其他一些半导体;本领域未来几年的研究热点将集中于新型高效的Ag(Au)/半导体纳米复合光催化剂的微结构调控及其用于可见光驱动有机反应的机理研究。本文为基于SPR效应构建Ag(Au)/半导体纳米复合光催化剂的研究提供了有力的参考依据,并且指出Ag(Au)/半导体纳米复合光催化剂的研究是发展可见光高效光催化剂的重要方向。     

Multiple defects induced near-infrared self-luminescence of (Ca,Sr)LaMgTaO6 double perovskite phosphor

Conventional near-infrared luminescent phosphors activated by transition metal elements or rare earth activators were already widely reported. In this work, we develop a self-activated near-infrared luminescent phosphor with a typical double perovskite structure, which exhibits an emission at 650–750 nm under excitation at 365 nm. The origin of the desired luminescence in (Ca,Sr)LaMgTaO₆ compounds is attributed to the oxygen vacancies defects, oxygen interstitial defects and substitution defects and antioccupation defects. Thermal quenching of photoluminescence is undesirable with an integrated emission loss of 30–50% at 150 °C, which needs to be improved. This new series of near-infrared luminescent materials have potential applications in agricultural cultivations and bio-imaging materials. More importantly, we demonstrate a strategy by self-activation to realize near-infrared light.     

Multi‐Dimensional Quantum Nanostructures with Polarization Properties for Display Applications

Colloidal semiconductor nanocrystals (NCs), or quantum nanostructures with various dimensions and morphologies, are excellent emerging solution‐processable luminescent materials for display applications. The future of semiconductor NCs in the display market strongly relies on the development of low energy consuming devices. Replacing spherical NCs with multi‐dimensional nanostructures that emit linearly or circularly polarized light with high color purity and brightness, can significantly enhance the performance and efficiency of future display devices. In this review, we highlight some recent advances of colloidal syntheses of multi‐dimensional quantum nanostructures and their implementation as polarized light sources. The most representative examples are quasi‐one‐dimensional (q‐1D) CdSe/CdS dot‐in‐rods with strong linearly polarized emission for liquid crystal display technologies, and two‐dimensional (2D) nanoplatelets with enhanced circular dichroism signals as potential circularly polarized luminescence sources for electroluminescence applications.     

Interfacial phenomena between conjugated organic molecules and noble metals

Understanding interfacial interaction between conjugated organic molecules and noble metals is important not only for surface science, but also in relation to organic epitaxy, the architecture of intermolecular networks or nanostructures, and organic electronics. Particularly, properties of interfacial geometric and electronic structures and their related phenomena have attracted much interest for their potential in various electronic and optoelectronic applications, and thus extensive efforts have been devoted to understand and control organic/metal interfaces. We provide an overview of interfacial phenomena between conjugated organic molecules and noble metals via various interactions at the organic/metal interfaces such as surface-molecule and intermolecular interactions, as well as recent progress achieved in this area.     

贵金属/WO3复合纳米晶的气敏与光催化研究进展

WO3作为新型的气敏材料和光催化剂具有广阔的应用前景,通过贵金属纳米簇修饰后的WO3复合纳米晶比WO3基体材料在性能上大幅提高。本文综述了贵金属修饰对WO3基体气敏和光催化性能的影响,其中气敏性能以不同敏感气体(如NOx、H2S、H2等)为分类依据,而光催化性能以不同贵金属(Au、Ag、Pt等)添加剂为分类依据,系统综述了贵金属/WO3复合纳米晶的气敏和光催化性能研究最新进展,并总结了常见贵金属/WO3的气敏和光催化机理模型,提出了贵金属/WO3在气敏和光催化应用过程中存在的问题及前景展望。     

Evolution of aluminum nitride nanostructures from nanoflower to thin film on silicon substrate by direct nitridation of aluminum precursor

Herein we demonstrate a convenient regulation of several aluminum nitride nanostructures through direct nitridation of aluminum precursor under different conditions. Different AlN nanostructures including conic nanoflowers, nanowires, quasi-aligned nanocones and polycrystalline thin film have been obtained on the Au-coated Si substrates just simply by decreasing the reaction temperature or changing the reaction procedure, and a four-stage growth mechanism is hereby deduced. The conic nanoflower composed of AlN nanocones is an interesting geometry. The photoluminescence and field emission measurement revealed that these AlN nanoflowers own a broad blue emission band and a rather good field emission property, suggesting the potential applications in light and field emission nanodevices.     

Hierarchical ZnO/Ag nanocomposites for plasmon-enhanced visible-light photocatalytic performance

Surface plasmon resonance (SPR) of the noble metals improve the photocatalytic activity of semiconductor metal oxides in the visible light region. This work reports the facile preparation of SPR induced visible light active hierarchical ZnO/Ag nanocomposite photocatalysts by using environmental friendly two-step method. The prepared nanocomposites analyzed by using various techniques such as powder-XRD, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, photoluminescence spectroscopy, and photocurrent measurements. The results indicate the formation of hierarchical ZnO/Ag nanocomposites, which shows surface plasmon absorbance and enhanced photocurrent responses. Because of the SPR effect, the nanocomposites show improved visible light photocatalytic activity by enhancing the electron-hole pair separation in Rhodamine B degradation system.     

Different sized luminescent gold nanoparticles

After a decade's efforts, a large amount of highly luminescent metal nanoparticles with different sizes and surface chemistries have been developed. While the luminescence is often attributed to particle size effects, other structural parameters such as surface ligands, valence states of metal atoms and crystallinity of nanoparticles also have a significant influence on emission properties and mechanisms. In this review, we summarized the strategies used to create luminescent gold nanoparticles with sizes from few to millions of atoms and discussed how these structural factors affect their photoluminescence.     

Impacts of core-shell structures on properties of lanthanide-based nanocrystals: crystal phase, lattice strain, downconversion, upconversion and energy transfer

This feature article highlights the new development and current status of rare-earth (RE) based core-shell nanocrystals, which is one of the new classes of hybrid nanostructures. Attractive properties of rare-earth based nanomaterials include extremely narrow emission bands, long lifetimes, large Stoke's shifts, photostability and absence of blinking that can be exploited for biophotonic and photonic applications. Core-shell nanostructures have been attracting a great deal of interest to improve the luminescence efficiency by the elimination of deleterious cross-relaxation. The main focus of this feature article is to address the impacts of core-shell structures on the properties of lanthanide based nanocrystals including crystal phase, lattice strain, downconversion emission, upconversion emission and energy transfer. We describe general synthetic methodologies to design core-shell nanostructure materials. An interesting finding reported is that the local environment of an ion in the core-shell structure significantly affects the modifications of radiative and nonradiative relaxation mechanisms. Finally, a tentative outlook on future developments of this research field is given. Here, we attempt to identify the critical parameters governing the design of luminescent lanthanide based core-shell nanostructures.     

A facile synthesis of a novel optoelectric material: a nanocomposite of SWCNT/ZnO nanostructures embedded in sulfonated polyaniline

Functionalized single-walled carbon nanotubes (f-SWCNTs) hybridized with freshly prepared zinc oxide (ZnO) nanocrystals have been found to be good luminescent material with tuned emission properties. A three-phase nanocomposite of sulfonated polyaniline embedded with such SWCNT/ZnO nanostructures has been prepared by a simple solution mixing chemical process and characterized by using high-resolution transmission electron microscopy, X-ray diffractometry, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The study of UV-visible absorption and photoluminescence spectroscopies reveal that the ternary polymer nanocomposite is a luminescent material with enhanced emission intensity. Also an increase in DC conductivity indicates that the nanocomposite is also a good conductive material, satisfying Mott’s variable range hopping model for a two-dimensional conduction. Such a three-phase nanocomposite may find extensive application in dye-sensitized solar cells, sensors, and supercapacitors.     

Synthesis, characterization and optical properties of Mg(OH)2 micro-/nanostructure and its conversion to MgO

Magnesium hydroxide (Mg(OH)₂) micro- and nanostructures have been synthesized by a single step hydrothermal route. Surface morphology analysis reveals the formation of micro- and nanostructures with varying shape and size at different synthesis conditions. Structural investigations by X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm that the synthesized material is Mg(OH)₂ with hexagonal crystal structure. An optical band gap of 5.7 eV is determined for Mg(OH)₂ nanodisks from the UV–vis absorption spectrum. A broad emission band with maximum intensity at around 400 nm is observed in the photoluminescence (PL) spectra of Mg(OH)₂ nanodisks at room temperature depicting the violet emission, which can be attributed to the ionized oxygen vacancies in the material. Furthermore, Mg(OH)₂ has been converted to MgO by calcination at 450 °C. Optical studies of the MgO nanodisks have shown an optical band gap of 3.43 eV and a broadband PL emission in the UV region. Mg(OH)₂ and MgO nanostructures with wide-band gap and short-wavelength luminescence emission can serve as a better luminescent material for photonic applications.     

State of arts on the bio-synthesis of noble metal nanoparticles and their biological application

Nanomaterials are materials in which at least one of the dimensions of the particles is 100 nm and below. There are many types of nanomaterials, but noble metal nanoparticles are of interest due to their uniquely large surface-to-volume ratio, high surface area, optical and electronic properties, high stability, easy synthesis, and tunable surface functionalization. More importantly, noble metal nanoparticles are known to have excellent compatibility with bio-materials, which is why they are widely used in biological applications. The synthesis method of noble metal nanoparticles conventionally involves the reduction of the noble metal salt precursor by toxic reaction agents such as NaBH₄, hydrazine, and formaldehyde. This is a major drawback for researchers involved in biological application researches. Hence, the bio-synthesis of noble metal nanoparticles (NPs) by bio-materials via bio-reduction provides an alternative method to synthesize noble metal nanoparticles which are potentially non-toxic and safer for biological application. In this review, the bio-synthesis of noble metal nanoparticle including gold nanoparticle (AuNPs), silver nanoparticle (AgNPs), platinum nanoparticle (PtNPs), and palladium nanoparticle (PdNPs) are first discussed. This is followed by a discussion of these biosynthesized noble metal in biological applications including antimicrobial, wound healing, anticancer drug, and bioimaging. Based on these, it can be concluded that the study on bio-synthesized noble metal nanoparticles will expand further involving bio-reduction by unexplored bio-materials. However, many questions remain on the feasibility of bio-synthesized noble metal nanoparticles to replace existing methods on various biological applications. Nevertheless, the current development of the biological application by bio-synthesized noble metal NPs is still intensively ongoing, and will eventually reach the goal of full commercialization.     

Ethylene glycol-assisted ultrafast synthesis and luminescent properties of novel multifunctional EuSr2F7 and TbSr2F7 nanostructures for WLEDs,displays and anti-counterfeiting

In this paper, novel EuSr₂F₇ and TbSr₂F₇ nanostructures were successfully synthesized via an ultrafast wet-chemical route at room temperature. The elemental compositions, morphology, luminescent behaviors, thermal stability, decay curves and quantum yields of the as-prepared samples were investigated. The fabricated white light-emitting diodes (WLEDs) exhibited excellent color rendering index and correlated color temperature values. The security inks and soft polydimethylsiloxane films were prepared for potential anti-counterfeiting and flexible display applications. Eventually, under low accelerating voltage and filament current, the as-prepared samples showed strong cathodoluminescence emission intensity. The above results suggest that the novel EuSr₂F₇ and TbSr₂F₇ nanostructures with outstanding luminescent performances could be promising for field-emission displays, WLEDs, flexible display films, and anti-counterfeiting applications.     

Anomalous luminescence phenomena of indium-doped ZnO nanostructures grown on Si substrates by the hydrothermal method

In recent years, zinc oxide (ZnO) has become one of the most popular research materials due to its unique properties and various applications. ZnO is an intrinsic semiconductor, with a wide bandgap (3.37 eV) and large exciton binding energy (60 meV) making it suitable for many optical applications. In this experiment, the simple hydrothermal method is used to grow indium-doped ZnO nanostructures on a silicon wafer, which are then annealed at different temperatures (400°C to 1,000°C) in an abundant oxygen atmosphere. This study discusses the surface structure and optical characteristic of ZnO nanomaterials. The structure of the ZnO nanostructures is analyzed by X-ray diffraction, the superficial state by scanning electron microscopy, and the optical measurements which are carried out using the temperature-dependent photoluminescence (PL) spectra. In this study, we discuss the broad peak energy of the yellow-orange emission which shows tendency towards a blueshift with the temperature increase in the PL spectra. This differs from other common semiconductors which have an increase in their peak energy of deep-level emission along with measurement temperature.     

Ordered macroporous bimetallic nanostructures: design, characterization, and applications

Ordered porous metal nanomaterials have current and future potential applications, for example, as catalysts, as photonic crystals, as sensors, as porous electrodes, as substrates for surface-enhanced Raman scattering (SERS), in separation technology, and in other emerging nanotechnologies. Methods for creating such materials are commonly characterized as "templating", a technique that involves first the creation of a sacrificial template with a specific porous structure, followed by the filling of these pores with desired metal materials and finally the removal of the starting template, leaving behind a metal replica of the original template. From the viewpoint of practical applications, ordered metal nanostructures with hierarchical porosity, namely, macropores in combination with micropores or mesopores, are of particular interest because macropores allow large guest molecules to access and an efficient mass transport through the porous structures is enabled while the micropores or mesopores enhance the selectivity and the surface area of the metal nanostructures. For this objective, colloidal crystals (or artificial opals) consisting of three-dimensional (3D) long-range ordered arrays of silica or polymer microspheres are ideal starting templates. However, with respect to the colloidal crystal templating strategies for production of ordered porous metal nanostructures, there are two challenging questions for materials scientists: (1) how to uniformly and controllably fill the interstitial space of the colloidal crystal templates and (2) how to generate ordered composite metal nanostructures with hierarchical porosity. This Account reports on recent work in the development and applications of ordered macroporous bimetallic nanostructures in our laboratories. A series of strategies have been explored to address the challenges in colloidal crystal template techniques. By rationally tailoring experimental parameters, we could readily and selectively design different types of ordered bimetallic nanostructures with hierarchical porosity by using a general template technique. The applications of the resulting nanostructures in catalysis and as substrates for SERS are described. Taking the ordered porous Au/Pt nanostructures as examples for applications as catalysts, the experimental results show that both the ordered hollow Au/Pt nanostructure and the ordered macroporous Au/Pt nanostructure exhibit high catalytic ability due to their special structural characteristics, and their catalytic activity is component-dependent. As for SERS applications, primary experimental results show that these ordered macroporous Au/Ag nanostructured films are highly desirable for detection of DNA bases by the SERS technique in terms of a high Raman intensity enhancement, good stability, and reproducibility, suggesting that these nanostructures may find applications in the rapid detection of DNA and DNA fragments.     

Au nanoparticles embedded inverse opal photonic crystals as substrates for upconversion emission enhancement

Photonic crystals (PCs) with periodic dielectric structures are capable to control the propagation of photons when photon energy is in the region of photonic band gap. The upconversion luminescence (UCL) of nanocrystals coated on the PCs surface can be enhanced by the PCs effects. While surface plasmon resonance (SPR) of noble metal nanoparticles (NPs) is being extensively applied to enhance the UCL properties of nanocrystals. However, the PCs or SPR effect are developed separately for the UCL enhancement. In this work, we present a facile preparation method of the Au NPs embedded inverse opals, which was used as substrates to improve the UCL properties of NaYF₄:Yb³⁺, Er³⁺ NPs. The significant luminescence enhancement of NaYF₄:Yb³⁺, Er³⁺ upconverting NPs was obtained by the coupling between the SPR of Au NPs and PCs effects from Au NPs embedded inverse opals substrates. The finding demonstrated that the Au NPs embedded inverse opals as substrates may be useful for the enhanced UCL of other phosphors, producing novel photonic devices.     

NIR enhancement induced by refractive index differences between noble metal particles and nanocrystals in glass-ceramics

The use of optically active ions doped into photonic media containing noble metals is an intriguing area of photoluminescence (PL) research. In this paper, we present a new approach using nickel ions doped into photonic glass ceramics (GCs) containing Au metal NCs. We exploit the unique PL properties of Ni²⁺ embedded in ZnAl₂O₄ nanocrystals (NCs). Under the same conditions, the Au-ZAO duplex samples exhibit 2–3 times higher near-infrared (NIR) emission intensity and higher absorption intensity compared to the samples without Au metal. We provide direct evidence of energy harvesting around NCs through numerical simulations. The significant NIR PL properties of Ni²⁺ in Au-ZAO GCs can be explained by the significant dielectric coefficient difference between the Au metal, the surrounding medium, and the ZAO NCs. Furthermore, the intense and broad emission spectra of our samples cover the entire second biological NIR region, which makes them particularly useful for biomedical applications.     

Energy transfer from luminescent centers to Er3+ in erbium-doped silicon-rich oxide films

The energy transfer mechanism between luminescent centers (LCs) and Er³⁺ in erbium-doped silicon-rich oxide (SROEr) films prepared by electron beam evaporation is investigated. Intense photoluminescence of the LCs (weak oxygen bonds, neutral oxygen vacancies, and Si=O states) within the active matrixes is obtained. Fast energy transfer from Si=O states to Er³⁺ takes advantage in the SROEr film and enhances the light emission from Er³⁺. The introduction of Si nanoclusters, which induces the Si=O states and facilitates the photon absorption of the Si=O states, is essential to obtain intense photoluminescence from both Si=O states and Er³⁺.     

A Present Understanding of Colloidal Quantum Dot Blinking

Luminescence intermittency, also termed ‘blinking’, refers to spontaneous changes in the brightness of a luminescent fluorophore under continuous optical excitation. Blinking was first observed in colloidal semiconductor nanocrystals over fifteen years ago, shortly after synthetic protocols became advanced enough to produce brightly luminescent nanocrystals. The underlying physical mechanism was initially associated with long-lived photo-induced charging of the nanocrystals. In recent years, however, significant evidence has accumulated to point at a more complex physical picture of the process, which involves several distinct mechanisms and is mediated by surface charge trapping. In parallel, efforts to synthesize highly luminescent semiconductor nanocrystals that do not exhibit blinking have recently borne fruit. We review the recent progress in understanding of blinking and potential applications in bioimaging using inorganic fluorescent tags.     

A surface-enhanced Raman spectroscopy study of thin graphene sheets functionalized with gold and silver nanostructures by seed-mediated growth

We describe a simple method for decorating graphene (1–5 layers) with Au and Ag nanostructures (nanoparticles, nanorods, and nanoplates). We deposit graphene electrostatically from highly-oriented pyrolytic graphite onto Si/SiO₂ surfaces functionalized with (aminopropyl)trimethoxysilane and grow the metal nanostructures by a seed-mediated growth method from hexanethiolate-coated Au monolayer-protected cluster “seeds” that are attached to graphene by hydrophobic interactions. Scanning electron microscopy reveals the selective growth of Au or Ag nanostructures on the graphene surface. In the case of Au, the low pH 2.8 growth solution causes etching of the graphene and formation of scroll-like structures. For Ag, the high pH 9.3 solution does not seem to affect the graphene. Raman spectroscopy is consistent with the graphene morphology and reveals that the presence of Au and Ag nanostructures increases the Raman scattering from the graphene by a factor of about 45 and 150, respectively. This work demonstrates a simple method for decorating graphene with noble metal nanostructures that may have interesting optical, electronic, and chemical properties for applications in nanoelectronics, sensing, and catalysis.