Interfacial Effects in the Relaxation Dynamics of Silver Nanometal-Glass Composites Probed by Transient Grating Spectroscopy

Relaxation dynamics of silver nanoparticles (NPs) embedded in glass have been studied by picosecond time-resolved transient grating (TG) spectroscopy. Phosphate-based glasses were prepared by melting and heat-treatment processes by which two different nanometal-glass composites were produced. The first is a glass system containing silver and tin in which Ag NPs are embedded in the matrix upon heat treatment. The second is a heat-treated silver-doped glass with spectroscopic indications of Ag⁺–Ag⁰ pairs located at or near the surface of the NPs. The time evolution of the light-induced TG for the Ag/Sn-doped glass shows an uncommon relaxation on the nanosecond time scale. Such behavior is explained in terms of energy transfer processes between polaronic and/or excitonic states in the near-interface region of the glass matrix and the NPs. In contrast, a faster monotonic relaxation is observed for the Ag-doped nanocomposite. This result is attributed to Ag NP → Ag⁺–Ag⁰ plasmon resonance energy transfer.     

Synthesis of silver nanoparticles and the optical properties

Silver nanoparticles (NPs) of 5-15 nm are synthesized with the reduction of silver nitrate (AgNO3 ) by formaldehyde (HCHO) and using polyethylenemine (PEI) as a stabilizer. Transmission electron microscopy (TEM) analysis shows the size of the Ag NPs increases with the increase of HCHO contents. The absorption and emission peaks of the original colloids are red shifted with increasing the size of Ag NPs. The absorption and emission peaks are at 344 nm, 349 nm, 357 nm, 362 nm, 364 nm and 444 nm, 458 nm, 519 nm, 534 nm, 550 nm, respectively. The fluorescence intensities of the silver colloids increase with increasing the NPs size (or the contents of HCHO). With the diluted fold increasing, the fluorescence intensity of the diluted silver colloids increases firstly then decreases. Compared with that of the original silver colloids, the emission peaks are blue shifted. For the diluted silver colloids, when the fluorescence intensity is maximum, the emission peaks are all near 444 nm. The 16-fold diluted silver colloid gets to the maximum emission intensity when the mole ratio of AgNO3 and HCHO is 1:6.     

Ag纳米颗粒对Er3+/Tm3+/Yb3+共掺铋锗酸盐玻璃上转换发光特性的影响

采用传统熔融淬冷法制备了系列Er³⁺/Tm 3+/Yb³⁺共掺复合Ag纳米颗粒的铋锗酸盐玻璃样品。从吸收光谱中 确定了Ag纳米颗粒表面等离子体共振(SPR)峰位于545nm附近;透射 电镜(TEM)图像中观察到均匀分布的Ag纳米颗粒,尺寸 约为6～18nm。研究了纳米Ag含量对Er3＋/Tm3＋ 共掺复合Ag纳米颗粒铋锗酸盐玻璃上转换发光特性的影响,结果表 明,Tm³⁺离子472nm处的上转换蓝光、Er³⁺离子525nm处的上转换绿光、543nm处的上转换 绿光和661nm处的上转换红光发光强度在AgCl含量的质量百分数为 1%时达到最大值,与未掺杂AgCl的基质玻璃相比,分别提高了约3.2、3.8、5.4倍。     

Enhancement of dual-broadband NIR emissions in Ag NPs embedded tellurite glass doped with Er3+/Tm3+/Ho3+ ions

Tellurite glasses combined with metal silver nanoparticles (Ag NPs) and Er3+/Tm3+/Ho3+ ions were synthesized using melting and quenching technique, and the enhanced two-band near-infrared (NIR) fluorescence induced by Ag NPs was reported. Upon the excitation of 808 nm laser diode (LD), dual-broadband and flat NIR fluorescence ranging from 1 350 nm to 1 600 nm and from 1 600 nm to 2 200 nm with full width at half maximum (FWHM) of 154 nm and 374 nm respectively in Ag NPs embedded tellurite glass doped with appropriate concentrations of Er3+/Tm3+/Ho3+ ions has an obvious enhancement of about 40% with respect to the glass sample without Ag NPs, which is attributed to the local field effect caused by Ag NPs and energy transfer from Ag species to rare-earth ions. The enhanced dual-broadband and flat NIR fluorescence enables us to develop various NIR band photonic devices flexibly.     

Painting and Direct Writing of Silver Nanostructures on Phosphate Glass with Electron Beam Irradiation

Surfaces with silver nanostructures are useful, due to their potential to resonate strongly with visible light. This report demonstrates a process for the directed extraction of silver at the surface of a transparent superionic conductor. A focused electron beam incident on superionic AgIAgPO₃ glass results in localized negative charge deposition, which is neutralized by the electrochemical reduction of free silver ions. This process was characterized for beam energies ranging from 1 to 12 kV and primary beam fluence ranging from 50 pC μm^?2 to 35 nC μm^?2. For electron fluence less than 2.5 nC μm^?2 the process produces vibrant coloration of the glass which can be tuned throughout the entire visible spectrum. Fluence greater than 2.5 nC μm^?2 results in the controlled writing of bulk silver on the surface, with a minimum line width as small as 400 nm and narrow gaps as small as 50 nm. The high ionic conductivity of the substrate is shown to be a vital component to the process, allowing the wide range of colors to be produced along with the controlled, nondendritic growth of silver structures.     

Plasmonic Enhancement or Energy Transfer? On the Luminescence of Gold‐, Silver‐, and Lanthanide‐Doped Silicate Glasses and Its Potential for Light‐Emitting Devices

With the technique of synchrotron X‐ray activation, molecule‐like, non‐plasmonic gold and silver particles in soda‐lime silicate glasses can be generated. The luminescence energy transfer between these species and lanthanide(III) ions is studied. As a result, a significant lanthanide luminescence enhancement by a factor of up to 250 under non‐resonant UV excitation is observed. The absence of a distinct gold and silver plasmon resonance absorption, respectively, the missing nanoparticle signals in previous SAXS and TEM experiments, the unaltered luminescence lifetime of the lanthanide ions compared to the non‐enhanced case, and an excitation maximum at 300–350 nm (equivalent to the absorption range of small noble metal particles) indicate unambiguously that the observed enhancement is due to a classical energy transfer between small noble metal particles and lanthanide ions, and not to a plasmonic field enhancement effect. It is proposed that very small, molecule‐like noble metal particles (such as dimers, trimers, and tetramers) first absorb the excitation light, undergo a singlet‐triplet intersystem crossing, and finally transfer the energy to an excited multiplet state of adjacent lanthanide(III) ions. X‐ray lithographic microstructuring and excitation with a commercial UV LED show the potential of the activated glass samples as bright light‐emitting devices with tunable emission colors.     

自组装法制备团簇Ag纳米结构衬底及其SERS

采用自组装方法,在3-Aminopropyltrimethoxy silane(APS)分子修饰后的玻璃衬底表面,获得了二维Ag纳 米结构衬底。在波长为532nm激光激发下,研究了沉积在衬底表面的 Rhodamine 6G(Rh6G)分子的拉曼光谱特性。结 果表明,制备的二维Ag纳米结构衬底具有强的拉曼增强特性,增强因子可以达到 10⁷ 倍。这说明,在外光场作用下,制备的Ag纳米结构衬底表面能够形成的强局部电磁场分布, 可以有效提升探针分子的光谱辐射效率,从而获得高增强拉曼散射。     

Gold Core‐DNA‐Silver Shell Nanoparticles with Intense Plasmonic Chiroptical Activities

The strong plasmonic chiroptical activities of gold core‐DNA‐silver shell nanoparticles (NPs) are reported for the first time, using cytosine‐rich single‐stranded DNA as the template for the guidance of silver shell growth. The anisotropy factor of the optically active NPs at 420 nm reaches 1.93 × 10^?2. Their chiroptical properties are likely induced by the DNA–plasmon interaction and markedly amplified by the strong electromagnetic coupling between the gold core and silver shell.     

A Transparent,Smooth, Thermally Robust,Conductive Polyimide for Flexible Electronics

In this work, a thermally and mechanically robust, smooth transparent conductor composed of silver nanowires embedded in a colorless polyimide substrate is introduced. The polyimide is exceptionally chemically, mechanically, and thermally stable. While silver nanowire networks tend not to be thermally stable to high temperatures, the addition of a titania coating on the nano­wires dramatically increases their thermal stability. This allows for the polyimide to be thermally imidized at 360 °C with the silver nanowires in place, creating a smooth (<1 nm root mean square roughness), conductive surface. These transparent conducting substrate‐cum‐electrodes exhibit a conductivity ratio figure of merit of 272, significantly outperforming commercially available indium‐tin‐oxide (ITO)‐coated plastics. The conductive polymide is subjected to various mechanical tests and is used as a substrate for a thermally deposited, flexible, organic light‐emitting diode, which shows improved device performance compared to a control device made on ITO coated glass.     

Precise Molecular Engineering of Photosensitizers with Aggregation‐Induced Emission over 800 nm for Photodynamic Therapy

Owing to efficient singlet oxygen (¹O₂) generation in aggregate state, photosensitizers (PSs) with aggregation‐induced emission (AIE) have attracted much research interests in photodynamic therapy (PDT). In addition to high ¹O₂ generation efficiency, strong molar absorption in long‐wavelength range and near‐infrared (NIR) emission are also highly desirable, but difficult to achieve for AIE PSs since the twisted structures in AIE moieties usually lead to absorption and emission in short‐wavelength range. In this contribution, through acceptor engineering, a new AIE PS of TBT is designed to show aggregation‐induced NIR emission centered at 810 nm, broad absorption in the range between 300 and 700 nm with a large molar absorption coefficient and a high ¹O₂ generation efficiency under white light irradiation. Further, donor engineering by attaching two branched flexible chains to TBT yielded TBTC8 , which circumvented the strong intermolecular interactions of TBT in nanoparticles (NPs), yielding TBTC8 NPs with optimized overall performance in ¹O₂ generation, absorption, and emission. Subsequent PDT results in both in vitro and in vivo studies indicate that TBTC8 NPs are promising candidates in practical application.     

纳米银颗粒表面增强荧光效应与其覆盖率的关联

实验上获得了纳米银颗粒对光敏剂二氢卟吩f-甲醚(CPD4)的荧光增强效应,基于纳米银颗粒覆盖率对表面增强荧光效应的影响,初步探讨了荧光增强的物理增强机制。不同覆盖率纳米银基底表面吸附的CPD4的增强荧光结果显示,在低颗粒覆盖率时(<30%),激发效率和激发态分子衰减速率不依赖于覆盖率变化;当颗粒覆盖率大于30%接近40%时,激发效率和激发态分子衰减速率都得到提高。实验和理论结果均表明,相比于单个银纳米颗粒,颗粒覆盖率增加提高了颗粒间电磁耦合效应,能够产生更强的表面增强荧光效应。     

Fluorescence Quenching upon Binding of Copper Ions in Dye‐Doped and Ligand‐Capped Polymer Nanoparticles: A Simple Way to Probe the Dye Accessibility in Nano‐Sized Templates

The synthesis and properties of well‐defined core–shell type fluorescent metal‐chelating polymer nanoparticles NP, in the 15 nm diameter range, with a fluorophore (9,10‐diphenylanthracene: DPA) entrapped in the particle core and a selective ligand (1,4,8,11‐tetraazacyclotetradecane: Cyclam), grafted onto the surface are presented. NPs with different number of dye‐per‐particle are readily obtained by entrapment of the fluorophore within the polymer core. The ligand‐coated NPs exhibit a high affinity for Cu²⁺ ions in aqueous solution and quenching of the DPA fluorescence is observed upon binding of copper. The quenching of fluorescence arises through energy transfer (FRET) from the dye to the copper‐cyclam complexes that form at the NP surface with an operating distance (d) in the 2 nm range. A simple core–shell model accounts for the steady‐state and time‐resolved fluorescence titration experiments: dye molecules located in the outer sphere (thickness d) of the NPs are quenched while the fluorescence of dyes embedded more deeply is not affected by the binding of copper ions. The observed high quenching efficiency (60–65 %), which is tightly correlated to the volumic and microstructural features of the NPs, shed light on the enhanced accessibility inherent in nano‐sized templates. The response towards different metal ions was investigated and this confirmed the selectivity of the nanoparticle template‐assembled sensor for cupric ions.     

Silver‐Infused Porphyrinic Metal–Organic Framework: Surface‐Adaptive,On‐Demand Nanoplatform for Synergistic Bacteria Killing and Wound Disinfection

The fabrication of functional nanoplatforms for combating multidrug‐resistant bacteria is of vital importance. Among them, silver nanoparticles (Ag NPs) have shown an antibacterial effect; however, the remainder cores of Ag NPs after use might have a toxic effect on humans. Thus, Ag ions based materials have been fabricated to substitute Ag NPs for antibacterial applications. Nevertheless, the always‐on release state leads to the low biocompatibility, which limits their biomedical applications. In addition, the single effect also restricts their antibacterial ability. Herein, a powerful surface‐adaptive, on‐demand antimicrobial nanoplatform is fabricated by coating hyaluronic acid (HA) on Ag ions loaded photosensitive metal‐organic frameworks to exhibit a strong synergistic effect. The nanoplatform shows good biocompatibility with nontargeted cells, as negatively charged HA can prevent the release of Ag ions. While in the presence of targeted bacteria, the secreted hyaluronidase can degrade HA on the nanoplatform and produce positively charged nanoparticles, which display increased affinity to bacteria and show a strong synergistic antibacterial effect owing to the released Ag ions and generated reactive oxygen species under visible light irradiation. Importantly, due to the outstanding on‐demand antimicrobial performance, the nanoplatform also shows great effects on treating multidrug‐resistant bacteria infected wounds in mice models.     

Preparation of Ag Nanocomposite Tellurite Glass by Solid-State Field-Assisted Diffusion

Ag nanocomposite tellurite glass was successfully prepared by solid-state field-assisted diffusion. The chemical states of Ag, the microstructures of Ag nanoparticles (NPs), and the optical absorption properties were studied for the as-diffused samples. The formation mechanism of Ag NPs in the present tellurite glass is discussed compared with that in soda-lime silicate glass. The results showed that, although the tellurite glass matrix was free of alkali ions, Ag NPs could also be formed using solid-state field-assisted diffusion. This phenomenon is due to an inherently loose network in the present tellurite glass. Optical absorption in the as-diffused TeO₂-Nb₂O₅-BaO glass was strongly affected by the matrix composition and the process parameters. This work provides a promising method to prepare Ag nanocomposite tellurite glass.     

Streptavidin‐Functionalized Silver‐Nanoparticle‐Enriched Carbon Nanotube Tag for Ultrasensitive Multiplexed Detection of Tumor Markers

A streptavidin‐functionalized silver‐nanoparticle‐enriched carbon nanotube (CNT/Ag NP) is designed as trace tag for ultrasensitive multiplexed measurements of tumor markers using a disposable immunosensor array. The CNT/Ag NP nanohybrid is prepared by one‐pot in situ deposition of Ag NPs on carboxylated CNTs. The nanohybrid is functionalized with streptavidin via the inherent interaction between the protein and Ag NPs for further linkage of biotinylated signal antibodies to obtain tagged antibodies. The functionalization process greatly improves the dispersibility of the nanohybrid in water. The immunosensor array is prepared by covalently immobilizing capture antibodies on chitosan‐modified screen‐printed carbon electrodes. Through a sandwich‐type immunoreaction on the immunosensor array, numerous Ag NPs are captured onto every single immunocomplex and are further amplified by a subsequent Ag NP‐promoted deposition of silver from a silver enhancer solution to obtain the sensitive electrochemical‐stripping signal of the Ag NPs. Using carcinoembryonic antigen and α‐fetoprotein as model analytes, this proposed multiplexed immunoassay method shows acceptable precision and wide linear ranges over four orders of magnitude with detection limits down to 0.093 and 0.061 pg mL^?1, respectively. The assay results of serum samples with the proposed method are in acceptable agreement with the reference values. The newly designed strategy and the functionalized tag avoid cross‐talk and the requirement of deoxygenation for electrochemical immunoassay, and thus provide a promising potential in clinical application.     

Nd3+ doped fluorochlorozirconate glass:3.9 μm MIR emission properties and energy transfer

The Nd3+ doped fluorochlorozirconate (FCZ) glass was prepared by melt-quenching method. The 3.9 μm emission from Nd3+ ions is attributed to the two-photon absorption process. The strong emission transition at 3.9 μm fluorescence peak intensity, corresponding to the 4G11/2→2K13/2 transition, is directly proportional to the NaCl concentration. With the increase of the Cl- ions amount, the mid-infrared (MIR) luminescent intensity is significantly enhanced. Additionally, the Judd-Ofelt (J-O) parameter Ω2 is larger than that of the fluorozirconate (FZ) glass, which indicates the covalency of the bond between RE ions and ligand is stronger as Cl- ions substitution of F- ions in chloride FZ glass. The X-ray diffraction (XRD) patterns show that the amorphous glassy state keeps the FZ glass network structure. In brief, the advantageous spectroscopic characteristics make the Nd3+-doped FCZ glass be a promising candidate for application of 3.9 μm emission.     

Fabrication of Germanosilicate glass optical fibers containing Tm/sup 2+/ ions and their nonlinear optical properties

Germanosilicate glass optical fibers incorporated with the Tm/sup 2+/ ions were fabricated to enhance optical nonlinearity by providing a strong reduction environment based on the solution doping technique in the modified chemical vapor deposition (MCVD) process. The incorporation of the Tm/sup 2+/ ions into the fiber core was identified by the electron paramagnetic resonance (EPR) spectrum in the fiber preform, and the absorption and emission properties between 350 and 1600 nm of the Tm/sup 2+/ ions in optical fibers and the fiber preform. A strong broad absorption band due to the Tm/sup 2+/ ions appeared from 350 to /spl sim/900 nm, and a broad emission from /spl sim/600 to /spl sim/1050 nm and the other emission from /spl sim/1050 to /spl sim/1300 nm, which were not shown in the Tm/sup 3+/ ions, were found upon Ar-ion laser pumping at 515 nm. Both absorption and emission results confirm that the Tm/sup 2+/ ions in the germanosilicate glass have the 4f-5d energy band from 350 to /spl sim/900 nm and the 4f-4f energy level at /spl sim/1115 nm. Also, the resonant nonlinearity at /spl sim/1310 and /spl sim/1530 nm due to the Tm/sup 2+/ ions in the fiber was measured upon the 515 nm optical pumping by using a long-period fiber grating (LPG) pair method. The nonlinear refractive index n/sub 2/ at /spl sim/1310 and /spl sim/1530 nm was found to be /spl sim/4/spl times/10/sup -15/ m/sup 2//W, where 70% and 30% of the n/sub 2/ are attributed to the nonradiative transitions and the radiative transitions, respectively.     

Enhancement of dye sensitized solar cell efficiency via incorporation of upconverting phosphor nanoparticles as spectral converters

Upconverting NaYF₄:Yb³⁺,Er³⁺/NaYF₄ core‐shell (CS) nanoparticles (NPs) were synthesized by thermal decomposition of lanthanide trifluoroacetate precursors and mixed with TiO₂ NPs to fabricate dye‐sensitized solar cells (DSSCs). The CS geometry effectively prevents the capture of electrons because of the surface states and improves photo‐emission. The as‐synthesized CS NPs show upconversion (UC) luminescence, converting near infrared (NIR) light into visible light (450–700 nm), making the photon absorption by the ruthenium‐based dyes (which have little or no absorption in the NIR region) possible. The champion DSSCs fabricated using CS UC NPs (average size = 25 nm) show enhancements of ~12.5% (sensitized with black/N749 dye) and of ~5.5% (sensitized with N719 dye) in overall power conversion efficiency under AM 1.5G illumination. This variation in the enhancement of the DSSC efficiencies for black and N719 dyes is attributed to the difference in the extinction coefficient and the absorption wavelength range of dyes. Incident photon‐to‐current conversion efficiency measurements also evidently showed the photocurrent enhancement in the NIR region of the spectrum because of the UC effect. The results prove that the augmentation in efficiency is primarily due to NIR to visible spectrum modification by the fluorescent UC NPs. Copyright © 2015 John Wiley & Sons, Ltd.     

Silver Nanoparticles Deposited Layered Double Hydroxide Nanoporous Coatings with Excellent Antimicrobial Activities

Simple and facile processes to produce silver nanoparticles deposited layered double hydroxide (Ag‐LDH) coatings are reported. High quality nanoporous LDH coatings are obtained under hydrothermal conditions via an improved in situ growth method by immersing the substrates in LDH suspensions after removal of free electrolytes. Different types of substrates including metal, ceramics, and glass with planar and non‐planar surfaces can all be coated with the oriented LDH films with strong adhesion. The pore size can be easily tuned by changing the metal:NaOH ratio during the precipiation process of LDH precursors. In the presence of LDH coatings, silver ions can be readily reduced to metallic silver nanoparticles (Ag NPs) in aqueous solutions. The resulting Ag NPs are incorporated evenly on LDH surface. The Ag‐LDH coating exhibits excellent and durable antimicrobial activities against both Gram‐negative (E. Coli and P. Aeruginosa) and Gram‐positive (B. Subtilis and S. Aureus) bacteria. Even at the 4th recycled use, more than 99% of all types of bacteria can be killed. Moreover, the Ag‐LDH coating can also effectively inhibit the bacterial growth and prevent the biofilm formation in the nutrient solutions. These newly designed Ag‐LDH coatings may offer a promising antimicrobial solution for clinical and environmental applications.