Plasmonic and Nonlinear Optical Absorption Properties of Ag:ZrO2 Nanocomposite Thin Films

Ag nanoparticles (NPs) embedded in a zirconium oxide matrix in the form of Ag:ZrO₂ nanocomposite (NC) thin films were synthesized by using the sol–gel technique followed by thermal annealing. With the varying of the concentration of Ag precursor and annealing conditions, average sizes (diameters) of Ag nanoparticles (NPs) in the nanocomposite film have been varied from 7 to 20 nm. UV–VIS absorption studies reveal the surface plasmon resonance (SPR)-induced absorption in the visible region, and the SPR peak intensity increases with the increasing of the Ag precursor as well as with the annealing duration. A red shift in SPR peak position with the increase in the Ag precursor concentration confirms the growth of Ag NPs. Surface topographies of these NC films showed that deposited films are dense, uniform, and intact during the variation in annealing conditions. The magnitude and sign of absorptive nonlinearities were measured near the SPR of the Ag NPs with an open-aperture z-scan technique using a nanosecond-pulsed laser. Saturable optical absorption in NC films was identified having saturation intensities in the order of 10¹² W/m². Such values of saturation intensities with the possibility of size-dependent tuning could enable these NC films to be used in nanophotonic applications.     

Influence of SiO<Subscript>2</Subscript> Spacer Layer Thickness on Performance of Plasmonic Textured Silicon Solar Cell

We investigated the effect of SiO₂ spacer layer thickness between the textured silicon surface and silver nanoparticles (Ag NPs) on solar cell performance using quantum efficiency analysis. Separation of Ag NPs from high index silicon with SiO₂ layer led to modified absorption and scattering cross-sections due to graded refractive index medium. The forward scattering from Ag NPs is very sensitive to SiO₂ layer thickness in plasmonic silicon cell performance due to the evanescent character of generated near-fields around the NPs. With the optimized ～30–40 nm SiO₂ spacer layer, we observed an enhancement of solar cell efficiency from ～8.7 to ～10 %, which is due to the photocurrent enhancement in the off-resonance surface plasmon region. We also estimated minority carrier diffusion lengths (L _eff) from internal quantum efficiency data, which are also sensitive to SiO₂ spacer layer thickness. We observed that the L _eff values are enhanced from ～356 to ～420 μm after placing Ag NPs on ～40 nm spacer layer due to improved forward (angular) scattering of light from the Ag NPs into silicon.     

Dopamine-Induced Growth of Au and Ag Nanoparticles on ITO Substrate and Their Application in PCPDTBT-Based Polymer Solar Cell

The direct attachment and growth of gold or silver nanoparticles (NPs) on indium tin oxide (ITO) surfaces was demonstrated using a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method by chemical reduction of the precursor metal salts with dopamine aqueous solution. Ag NPs on ITO substrate were approximately spherical with an average particle size of about 57 nm, but had a wide particle size distribution. Compared with Ag NPs, under the same 10 SILAR cycles, Au NPs have higher density packing and smaller average particle size of about 36 nm. XRD characterization and surface chemistry analysis confirmed the formation of Ag and Au NPs on ITO substrate with small amounts of dopamine-quinone adsorbed on the surface of them. Although Au NPs showed characteristic plasmon absorption, this did not result in performance enhancement in solar cell with the structure of ITO/ZnO/PCPDTBT:[6,6]-phenyl C₇₁/MoO₃/Ag because of the energy level mismatch between ZnO and dopamine molecules adsorbed on the surface of metal NPs.     

Influence of Plasmonic Silver Nanoparticles on Fluorescence Quenching of 1,4-dihydroxy-3-methylanthracene-9,10-dione

Optical absorption and fluorescence emission techniques were employed to investigate the size effects of silver nanoparticles (Ag NPs) on 1,4-dihydroxy-3-methylanthracene-9,10-dione (DHMAD). Silver nanoparticles of different sizes were prepared by Creighton method under microwave irradiation. The prepared Ag NPs show the surface plasmon band around 400 nm. Fluorescence quenching of DHMAD by Ag NPs was found to increase with an increase in the size of Ag NPs. The fluorescence quenching is explained by resonant energy transfer mechanism between DHMAD and Ag NPs, orientation of DHMAD on silver nanoparticles through chemisorptions. The Stern–Volmer quenching constant and Benesi–Hildebrand association constant for the above system were calculated. DFT calculations were also performed to study the ground and excited state behavior of DHMAD and DHMAD + Ag system.     

Spectral Investigations on the Fluorescence Quenching of 1,4-dihydroxy-2,3-dimethylanthracene-9,10-dione by Plasmonic Silver Nanoparticles

Silver nanoparticles (Ag NPs) of different sizes have been prepared by Lee and Meisel’s method using trisodium citrate as reducing agent under ultra sonication. Optical absorption and fluorescence emission techniques were employed to investigate the interaction of 1,4-dihydroxy-2,3-dimethyl anthracene-9,10-dione (DHDMAD) with silver nanoparticles. In fluorescence spectroscopic study, we used the DHDMAD and Ag NPs as component molecules for construction of Förster Resonance Energy Transfer (FRET), whereas DHDMAD serve as donor and Ag NPs as acceptor. The surface plasmon resonance (SPR) peak of the prepared silver colloidal solution was observed from 419 nm to 437 nm. The synthesized silver nanoparticles at different heating time intervals were spherical in shape about the size of 25 nm and 55 nm. The fluorescence interaction between silver nanoparticles and DHDMAD confirms the FRET mechanism. According to Förster theory, the distance between silver nanoparticles and DHDMAD and the critical energy transfer distance were calculated and it is increase with heating time.     

Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles

Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.

     

Plasmonically Tunable Blue-Shifted Emission from Coumarin 153 in Ag Nanostructure Random Media: A Demonstration of Fast Dynamic Surface-Enhanced Fluorescence

Enhancement of intensity and wavelength tunability of emission are desirable features for light-emitting device applications. We report on the large and tunable blue shift (60 nm) in emission from an environment-sensitive fluorophore (Coumarin153) embedded in Ag plasmonic random media. Coumarin 153 having emission at 555 nm, show a systematic blue shift (to 542, 503 and 495 nm) upon infiltration into random media fabricated by Ag nanowires of different aspect ratio (hence, surface plasmon resonances at 426, 445 and 464 nm). The blue shift is due to the fast dynamic surface-enhanced fluorescence mechanism and can be tuned by controlling the surface plasmon resonance and hotspot density in random media. Enhanced emission at desired wavelength is achieved by using nanostructures having higher extinction coefficient but same-surface plasmon resonance. Ag nanostructures of different aspect ratio used for fabricating the random media are synthesized by chemical route.     

Synthesis of Silver and Gold Nanoparticles Using Cashew Nut Shell Liquid and Its Antibacterial Activity Against Fish Pathogens

This study reveals a green process for the production of multi-morphological silver (Ag NPs) and gold (Au NPs) nanoparticles, synthesized using an agro-industrial residue cashew nut shell liquid. Aqueous solutions of Ag⁺ ions for silver and chloroaurate ions for gold were treated with cashew nut shell extract for the formation of Ag and Au NPs. The nano metallic dispersions were characterized by measuring the surface plasmon absorbance at 440 and 546 nm for Ag and Au NPs. Transmission electron microscopy showed the formation of nanoparticles in the range of 5–20 nm for silver and gold with assorted morphologies such as round, triangular, spherical and irregular. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analyses of the freeze-dried powder confirmed the formation of metallic Ag and Au NPs in crystalline form. Further analysis by Fourier transform infrared spectroscopy provided evidence for the presence of various biomolecules, which might be responsible for the reduction of silver and gold ions. The obtained Ag and Au NPs had significant antibacterial activity, minimum inhibitory concentration and minimum bactericidal concentration on bacteria associated with fish diseases.     

Blue-Shifted SPR of Au Nanoparticles with Ordering of Carbon by Dense Ionization and Thermal Treatment

Thin films of carbon-containing Au nanoparticles (NPs), prepared by the co-sputtering using a neutral Ar atom beam, were irradiated by 120 MeV Ag ions and also annealed, separately, at increasing temperatures in inert atmosphere. The surface plasmon resonance (SPR) band of the nanocomposite film was observed to be blue shifted (～50 nm) in both cases, with increasing fluence and temperature. The structural changes of Au NPs embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy. A growth of Au NPs was observed with increasing fluence and also with increasing temperature. A percolation of Au NPs was observed at 500 °C. A growth of Au NPs with ion irradiation is explained in the framework of a thermal spike model. Raman spectroscopy revealed the ordering of a-C thin films with increasing fluence and temperature, which is ascribed to a change of refractive index and the blue shift of the SPR band.     

Enhanced and Selective Photodetection Using Graphene-Stabilized Hybrid Plasmonic Silver Nanoparticles

We report the fabrication and characteristics of a novel graphene-Ag⁰ hybrid plasmonic nanostructure-based photodetector exhibiting moderately high responsivity (～28 mA/W) and spectral selectivity (～510 nm) in the visible wavelength. The formation of highly stable Ag⁰ nanoparticles with an average size of 40 nm is observed within the graphene layers, resulting in n-type doping of hybrid material. The absorption peak of graphene-Ag⁰ hybrid is redshifted to the visible wavelength (～510 nm) from the plasmonic Ag peak (～380 nm) in agreement with the optical simulation results for embedded metal nanoparticles. The study demonstrates the synergistic effect of the graphene-metal nanocomposite, which appears attractive for applications in graphene-based photonic devices.     

Plasmon-Assisted Enhancement and Tuning of Optical Properties in <Emphasis Type="Italic">β-</Emphasis>In<Subscript>2</Subscript>S<Subscript>3</Subscript> Quantum Dots

Exciton-plasmon coupling can significantly modify the spectral response of semiconductor quantum dots in a metal nanoparticle-semiconductor complex system. β-In₂S₃ quantum dots of size ～3 nm and Ag nanospheres of size ～100 nm were synthesized by chemical route and coated over glass substrates. In the strong coupling regime, the plasmons are shown to mediate indirect Coulomb interaction between the quantum dots. In the proximity of Ag plasmons, the excitonic binding energy of the β-In₂S₃ quantum dots increases by ～500 meV, indicating that the interaction potential between the quantum dots is positive and repulsive in nature. This interaction also leads to strong coupling of the defect levels in the SQD complex. The defect emission wavelength can be enhanced by an order of 10² or shifted from red region (～650 nm) to green (～550 nm) by controlling the plasmon-induced defect level coupling. The experimental observation demonstrates one of the theoretically predicted consequences of exciton-plasmon interaction. This work demonstrates the possibility of harnessing the potential of the two complimentary systems (semiconductor quantum dots and metal nanoparticles) to achieve controllable emission and absorption properties for fabrication of nano plasmonic devices.     

Zur Abbaubeschleunigung von Pflanzenschutzmittel-Wirkstoffen im Boden

In the current investigation, we report the biosynthesis of silver nanoparticles (Ag NPs) employing extract of Alternaria alternata, which is an eco-friendly process for the synthesis of metallic nanoparticles. Ag NPs were synthesised through the reduction of aqueous Ag⁺ ion using the cell extract of fungus A. alternata in the dark conditions. The synthetic process was relatively fast and Ag NPs were formed within 24 h. UV–visible spectrum of the aqueous medium containing silver ion showed a peak at 435?nm corresponding to the plasmon absorbance of Ag NPs and another peak at 280?nm refers to tyrosine amino acid. The nanoparticles were characterised by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The morphology of nanoparticles is found to be spherical mostly, with ranging size of 27–79?nm; as revealed by SEM. The FTIR spectrum analysis indicated that biomolecules were involved in the synthesis of Ag NPs. The presence of the amino groups is expected to pack differently around the Ag NPs. This in turn will influence the self-assembly of nanoparticles on substrates as well as their stability. The present study demonstrates the possible use of biologically synthesised Ag NPs in the field of agriculture, when A. alternata could be used for simple, nonhazardous and efficient synthesis of Ag NPs.     

Laser-Driven Precipitation and Modification of Silver Nanoparticles in Soda Lime Glass Matrix Monitored by On-line Extinction Measurements

In this work, we investigated the effect of nanosecond laser irradiation at 532?nm on precipitation of Ag nanoparticles (NPs) in soda lime glasses doped with silver in the Ag^?+??CNa^?+? ion-exchange process. Formation and subsequent modification of Ag NPs during laser irradiation were studied by on-line extinction measurements making use of the localized surface plasmon resonance (LSPR). These investigations were further completed using scanning and transmission electron microscopies to examine the average size and distribution of nanoparticles within the sample. It has been shown that formation of NPs, its kinetics and the particle size strongly depend on the fluence and the total number of deposited laser pulses. It has been found that Ag NPs form after some specific number of pulses and they rapidly grow in size and number until some maximal value of extinction has been reached. Further irradiation of such samples only results in destruction of precipitated NPs due to photo-breakup, laser ablation confirmed by strong plasma emission observation. Moreover, due to strong irradiation, the host matrix can also be affected by changing its refractive index which manifests as the blue shift of the LSPR.     

Optical and Nonlinear Optical Limiting Properties of AgNi Alloy Nanostructures

Silver-nickel alloy nanoparticles with varying size were synthesized by reducing the metal precursors chemically using a single-step solution-based synthesis route. The structural, optical, and nonlinear optical properties of the prepared samples were investigated. The synthesized samples having highly agglomerated, interconnected nature and found to exhibit dipole and multipole surface plasmon resonance related optical absorption bands. Nonlinear optical and optical limiting properties were investigated using a single beam open aperture z-scan technique with the use of 532 nm, 5-ns laser pulses. The nonlinearity observed was found to have contributions from saturable absorption (SA) and excited state absorption (ESA) related to free carriers. The effective nonlinear optical absorption was enhanced in AgNi alloy compared to pure Ag nanostructures.     

DNA Detection Based on Localized Surface Plasmon Resonance Spectroscopy of Ag@Au Biocomposite Nanoparticles

Noble metal nanoparticles (NPs) have attracted much attention due to their unique physical and chemical properties such as tunable surface plasmonics, high-efficiency electrochemical sensing, and enhanced fluorescence. We produced two biosensor chips consisting of Ag@Au bimetallic nanoparticles (BNPs) on a carbon thin film by simple RF-sputtering and RF-plasma-enhanced chemical vapor co-deposition. We deposited Au NPs with average size of 4 nm (Au₁ NPs) or 11 nm (Au₂ NPs) on a sensor chip consisting of Ag NPs with mean size of 15 nm, and we investigated the effect of shell size (Au NPs) on the chemical activities of the resulting Ag@Au₁ BNPs and Ag@Au₂ BNPs. We estimated the average size and morphology of Ag@Au BNPs by scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. X-ray diffraction (XRD) patterns revealed that Ag NPs and Au NPs had face-centered cubic (FCC) structure. We studied aging of the biosensor chips consisting of Ag@Au BNPs by localized surface plasmon resonance (LSPR) spectroscopy for up to 3 months. UV–visible aging of the prepared samples indicated that Ag@Au₁ BNPs, which corresponded to Ag NPs covered with smaller Au NPs, were more chemically active than Ag@Au₂ BNPs. Furthermore, we evaluated changes in the LSPR absorption peaks of Ag@Au₁ BNPs and bare Ag NPs in the presence of a DNA primer decamer at fM concentrations, to find that Ag@Au₁ BNPs were more sensitive biosensor chips within a short response time as compared to bare Ag NPs.

     

Effective Coupling of Incident Light Through an Air Region into an S-Shape Plasmonic Ag Nanowire Waveguide with Relatively Long Propagation Length

Coupling of incident light through an air region into an S-shape silver (Ag) plasmonic nanowire waveguide (SSAPNW) is a highly difficult challenge of light guiding on the surface of metal nanowire. In this paper, we numerically analyze the coupling effect of an SSAPNW which is covered by a dielectric medium using a finite element method. The coupling effect can be modulated by adjusting the Ag nanowire diameter and the covering dielectric medium width and wavelength of incident light, and the propagation length of surface plasmon (SP) coupling can be maximized. Simulation results reveal that the field confinement can be significantly improved and the majority of the electric field can be carried on the surface of a bending Ag nanowire. The effect of electric field transport along an SSAPNW due to SP coupling and Fabry-Perot resonance is investigated for different dimensions and lengths. Accordingly, long propagation lengths of about 41.5 μm for 10?×?SSAPNW at an incident wavelength of 810 nm and longer propagation length can be achieved if more sections of an SSAPNW are used. Simulation results offer an efficient method for optimizing SP coupling into bending metal nanowire waveguides and promote the realization of highly integrated plasmonic devices.     

Quantifying the Usefulness of Oxide-Encapsulated Silver Nanoparticles in Semiconducting Films

Incorporating plasmonic nanoparticles (NPs) in an organic solar cell (OSC) can improve device performance. In our simulation studies, at NP resonance, absorption in poly(3-hexythiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) can be increased by encapsulating 50 nm Ag NPs with Al₂O₃, HfO₂, MoO₃, and SiO₂. At Ag NP resonance, when the oxide thickness is significant enough, oxides with high relative permittivity induces a higher electric field enhancement at the metal/dielectric interface. This is translated to improved absorption in the polymer layer. By integrating against AM1.5G, overall absorption in P3HT/PCBM is improved when incorporating Ag NPs encapsulated with a thin oxide shell into the polymer film. However, polymeric absorption loss is induced for oxide-encapsulated Ag NPs if MoO₃ and SiO₂ shells are more than 5 nm. For Al₂O₃ and HfO₂, Ag NPs should not be encapsulated with shells thicker than 10 nm. Modeling studies are also extended to absorption in a CH₃NH₃PbI₃ perovskite layer. It is revealed that both Al₂O₃ and HfO₂ have an optimal shell thickness of about 20 nm to ensure maximum absorption in CH₃NH₃PbI₃. The results can be utilized as a useful guideline when designing photovoltaics from an optical point of view.     

Double-Layered Metal Nano-Strip Antennas for Sensing Applications

A coupled plasmonic system based on double-layered metal nano-strips for sensing applications is investigated by means of mode analysis and two-dimensional finite-difference time-domain simulations. The nano-strips act as optical antennas through constructive interference of short-range surface plasmon polaritons, thus increasing their scattering cross-section and optical field enhancement. Near-field modulation by optical trapped metal nanoparticles (NPs) is also demonstrated. Our results reveal that the device exhibits a refractive index sensitivity of ～200 nm/RIU, and a maximum surface-enhanced Raman scattering (SERS) factor of 10⁹–10¹⁰ from metal NPs trapped in the near-field region. The proposed device shows reasonable figure-of-merit and is ready for integration with common optofluidic biosensors.     

Fluorescence enhancement monitoring of pyrromethene laser dyes by metallic Ag nanoparticles

Fluorescence enhancement monitoring of pyrromethene laser dyes using their complexation with Ag nanoparticles (Ag NPs) was studied. The size of the prepared Ag NPs was determined by transmission electron spectroscopy and UV/Vis absorption spectroscopy. Mie theory was also used to confirm the size of NPs theoretically. The effect of different nanoparticle concentrations on the optical properties of 1 × 10^‐4 M PM dyes shows that 40%of Ag NPs concentration (40%C Ag NPs) in complex is the optimum concentration. Also, the effects of different concentrations of PM dyes in a complex was measured. Emission enhancement factors were calculated for all samples. Fluorescence enhancement efficiencies depended on the input pumping energy of a Nd‐YAG laser (wavelength 532 nm and 8 ns pulse duration) were reported and showed the lowest energy (28 and 32 mJ) in the case of PM567 and PM597, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Photocatalytic Reduction of CO2 into Methanol over Ag/TiO2 Nanocomposites Enhanced by Surface Plasmon Resonance

Ag-loaded TiO₂ (Ag/TiO₂) nanocomposites were prepared by microwave-assisted chemical reduction method using tetrabutyl titanate as the Ti source. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption isotherms, UV–vis absorption spectrum, X-ray photoelectron spectrum, photoluminescence spectrum, and Raman scattering spectrum, respectively. Results revealed that Ag nanoparticles (NPs) were successfully deposited on TiO₂ by reduction of Ag⁺, and the visible light absorption and Raman scattering of TiO₂ were enhanced by Ag NPs based on its surface plasmon resonance effect. Besides, Ag NPs could also effectively restrain the recombination of photogenerated electrons and holes with a longer luminescence life time. In addition, photocatalytic reduction of CO₂ with H₂O on the composites was conducted to obtain methanol. Experimental results indicated that Ag-loaded TiO₂ had better photocatalytic activity than pure TiO₂ due to the synergistic effect between UV light excitation and surface plasmon resonance enhancement, and 2.5 % Ag/TiO₂ exhibited the best activity; the corresponding energy efficiency was about 0.5 % and methanol yield was 405.2 μmol/g-cat, which was 9.4 times higher than that of pure TiO₂. Additionally, an excitation enhancement synergistic mechanism was proposed to explain the experimental results of photocatalytic reduction of CO₂ under different reaction conditions.