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.     

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.     

Use of ZnO:Tb down‐conversion phosphor for Ag nanoparticle plasmon absorption using a He–Cd ultraviolet laser

Although noble metal nanoparticles (NPs) have attracted some attention for potentially enhancing the luminescence of rare earth ions for phosphor lighting applications, the absorption of energy by NPs can also be beneficial in biological and polymer applications where local heating is desired, e.g. photothermal applications. Strong interaction between incident laser light and NPs occurs only when the laser wavelength matches the NP plasmon resonance. Although lasers with different wavelengths are available and the NP plasmon resonance can be tuned by changing its size and shape or the dielectric medium (host material), in this work, we consider exciting the plasmon resonance of Ag NPs indirectly with a He–Cd UV laser using the down‐conversion properties of Tb³⁺ ions in ZnO. The formation of Ag NPs was confirmed by X‐ray diffraction, transmission electron microscopy and UV–vis diffuse reflectance measurements. Radiative energy transfer from the Tb³⁺ ions to the Ag NPs resulted in quenching of the green luminescence of ZnO:Tb and was studied by means of spectral overlap and lifetime measurements. The use of a down‐converting phosphor, possibly with other rare earth ions, to indirectly couple a laser to the plasmon resonance wavelength of metal NPs is therefore successfully demonstrated and adds to the flexibility of such systems. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Contribution of LSP Effect to Light Absorption in Thin-Film Crystalline Silicon Solar Cells

Introducing periodic Ag gratings in the rear side of thin-film silicon excites localized surface plasmon (LSP) and Fabry-Perot (FP) effect. These two effects as well as an intrinsic one pass through absorption overlay together and all contribute to the light absorption in silicon. On the basis of electromagnetic field’s linear superposition, the absorptivity caused by LSP effect is separated from the overall absorptivity of a 500-nm-thick silicon and quantized by short current density. Finite difference time domain (FDTD) calculations were performed to obtain the absorptivity of silicon with different Ag grating parameters. The contribution of LSP effect to the light absorption is evaluated by photocurrent ratio and investigated under different Ag grating parameters. It is found that, as LSP effect is excited most intensively, the light absorption of silicon will also be enhanced extremely. By careful design, the overall short current density of silicon is optimized up to 25.4 mA/cm², where the contribution of LSP effect accounts for 38.6 %. Comparing to 14.5 mA/cm² for a reference silicon stack, it increases up to almost 75 %. These results may give design suggestions in implementation of plasmonic solar cell as high efficiency devices.     

Optical and Thermal Enhancement of Plasmonic Nanofluid Based on Core/Shell Nanoparticles

The plasmonic effect is introduced in solar thermal areas to enhance light harvest and absorption. The optical properties of plasmonic nanofluid are simulated by finite difference time domain (FDTD) method. Due to the excitation of localized surface plasmon resonance (LSPR) effect, an intensive absorption peak is observed at 0.5 μm. The absorption characteristics are sensitive to particle size and concentration. As the particle size increases, the absorption peak is broadened and shifted to longer wavelength. The absorption of SiO₂/Ag plasmonic nanofluid is improved gradually as the volume concentration increases, especially in the UV region. The absorption edge is shifted from 0.6 to 1.0 μm as the volume concentration increases from 0.001 to 0.01. The thermal simulation of suspended SiO₂/Ag nanoparticle shows a uniform temperature rise of 17.91 K under solar irradiation (AM 1.5), while under the same condition, the temperature rises in Ag nanoparticle and Al nanoparticle are 11.12 and 5.39 K, respectively. The core/shell plasmonic nanofluid exhibits a higher photothermal performance, which has a potential application in photothermal areas. A higher temperature rise can be obtained by improving the incident light intensity or optical absorption properties of nanoparticles.     

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.

     

Investigations on the Thermal Stability of Fullerene-Based (Ag-C<Subscript>70</Subscript>) Nanocomposite Thin Films

Fullerene-based bi-functional nanocomposite thin film (Ag nanoparticles embedded in fullerene C₇₀ matrix) is synthesized by thermal co-deposition method. Thermal stability of Ag-C₇₀ nanocomposite is investigated by annealing the nanocomposite thin film at different temperatures from 80 to 350 °C for 30 min. Optical and structural properties of nanocomposite thin film with respect to high temperature are studied by UV-visible spectroscopy and x-ray diffraction, respectively. Transmission electron microscopy is performed to observe the temperature-dependent size evolution of Ag nanoparticles in fullerene C₇₀ matrix. A large growth of Ag nanoparticles is observed with temperature especially above 200 °C due to enhanced diffusion of Ag in fullerene C₇₀ at higher temperature and Ostwald ripening. The properties of metal-fullerene nanocomposite is not significantly affected up to a temperature of 150 °C. With a further increase in temperature, a major blue shift of ~?33 nm in SPR wavelength is seen at a temperature of 300 °C due to the thermal induced structural transformation of fullerene C₇₀ matrix into amorphous carbon. A very large-sized Ag nanoparticle with a wide size distribution varying from 27.8 ± 0.6 to 330.0 ± 4.5 nm is seen at 350 °C and due to which, a red shift of ~?16 nm is obtained at this temperature. This study throws light on the thermal stability of the devices based on metal-fullerene bi-functional nanocomposite.     

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.     

Photocatalytic Activity of Ag/TiO2 Nanotube Arrays Enhanced by Surface Plasmon Resonance and Application in Hydrogen Evolution by Water Splitting

TiO₂ nanotube arrays (TiO₂ NTs) were fabricated by anodic oxidation and then Ag nanoparticles (Ag NPs) were assembled in TiO₂ NTs (Ag/TiO₂ NTs) by microwave-assisted chemical reduction. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence spectrum (PL), UV–vis absorption spectrum (UV–vis), and Raman spectrum, respectively. The results showed that Ag NPs were well dispersed on the surface of TiO₂ NTs with metallic state. The surface plasmon resonance (SPR) effect of Ag NPs could extend the visible light response and enhance the absorption capacity of TiO₂. Furthermore, Ag NPs could also restrain the recombination of photo-generated electron–hole pairs of TiO₂ NTs efficiently. The methylene blue photodegradation experiment proved that the SPR phenomenon had an effect on photoreaction enhancement. The results of photocatalytic water splitting indicated that Ag/TiO₂ NTs samples had better photocatalytic performance than pure TiO₂ NTs. The corresponding hydrogen evolution rate of Ag/TiO₂ NTs prepared with 0.002 M AgNO₃ solution was 3.3 times as that of pure TiO₂ NTs in the test condition. Additionally, the mechanism of catalyst activity enhanced by SPR effect was proposed.     

Single-Step Synthesis and Surface Plasmons of Bismuth-Coated Spherical to Hexagonal Silver Nanoparticles in Dichroic Ag:Bismuth Glass Nanocomposites

Here, we report for the first time the synthesis of bismuth-coated silver nanoparticles in dichroic bismuth glass nanocomposites by a novel and simple one-step melt quench technique without using any external reducing agent. The metallic silver nanoparticles (Ag NPs) were generated first, and subsequently, metallic bismuth was deposited on the Ag NPs and formed a thick layer. The reduction of Bi³⁺ to Bi^o and subsequently its deposition on the Ag NPs (which were formed earlier than Bi^o) in the K₂O–Bi₂O₃–B₂O₃ (KBB) glass system have been explained by their standard reduction potentials. The UV–vis absorption spectra show a prominent surface plasmon resonance (SPR) absorption band at 575 nm at lower concentrations (up to 0.01 wt%); three bands at 569, 624 and 780 nm at medium concentration (0.02–0.03 wt%); and two weak bands at 619 and 817 nm at highest concentration (0.06 wt%) of silver. They have been explained by the electrodynamics theories. TEM images reveal the conversion of spheroidal (5–15 nm) to hexagonal (10–35 nm) shaped Ag NPs with the increase in concentration of silver (up to 0.06 wt%). SAED pattern confirms the crystalline planes of rhombohedral bismuth and cubic silver. Thermal treatment at 360 °C, which is the glass transformation temperature (T _g) of the sample containing lower concentration of silver (0.007 wt%), shows red-shifted SPR band due to increase in size of NPs. Whereas the sample containing higher concentration (0.06 wt%) of silver under similar treatment exhibited changes in SPR spectral profile happened due to conversion to spherical NPs from hexagonal shape and reduction in size (10–20 nm) of NPs after heat treatment for 65 h. HRTEM images corroborate the different orientations of the NPs. FESEM images reveal hexagonal disk like structure having different orientations. Dichroic nature of the nanocomposites has been explained with the size and shape of Ag nanoparticles. We believe that this work will create new avenues in the area of nanometal–glass hybrid nanocomposites and the materials have significant applications in the field of optoelectronics and nanophotonics.     

Effect of Light Incident Angle on Fano Resonance Loss Mediation in Silver Nanoparticles Integrated Thin Silicon Wafers

In this work, we have studied the role of light incidence angle in the suppression of Fano resonance loss for mediating broadband light incoupling. At light normal incidence angle, the transmission loss of silver nanoparticles (Ag NPs) integrated 100 μm silicon (Si) wafer is reduced to ~?4 from ~?11%, and total reflectance is reduced to 32.7 from 38.7%. The reduction in reflectance is observed only in surface plasmon off-resonance region of the NPs, but the reflectance is enhanced slightly in surface plasmon resonance (SPR) region. With the change in light incident angles, we have observed a reduction in reflectance from NPs integrated silicon wafer at SPR region. At 40° light incident angle, the reflectance is reduced to 21 from 38.7% due to minimization of the Fano resonance in SPR region of the NPs. The Fano resonance loss reduction is explained based on modification in NPs’ dipole and quadrupole modes hybridization at the silicon interface with different light incident angles instead of normal incidence. Experimental observations are validated by simulating Ag NPs’ near-fields and angular distribution of far-fields at the silicon interface, scattering efficiency spectra at different light incident angles by finite difference time domain calculations.     

Investigating Fluorescence Quenching of ZnS Quantum Dots by Silver Nanoparticles

Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra having an absorbance edge at 300 nm and emission maxima (λ _emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process. The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K _sv value of 9 × 10⁹ M⁻¹. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm.     

Study of the Adsorption of Human Hemoglobin to Silver (Ag) Nanoparticle Surface for the Detection of the Unfolding of Hemoglobin

In the present report, we focused on the detail study of the optical properties and structural characterization of the Ag NPs for the nanobioconjugate analysis and detection of the conformational structural change of the Hb. The detail optical and structural analysis of Ag NPs has been studied from UV–Vis absorption, emission spectrum, XRD, and HRTEM study. The proteins/Hb are attached immediately onto Ag NPs surface when NPs touch the biological fluids, forming protein corona (PC), which gives their biological identity. The NPs-PC bioconjugate is, more specifically, the true identity of NPs in the physiological world. The adsorption of Hb with Ag NP surfaces has been studied by monitoring the soret band and tryptophan band of Hb. The dynamics of the Hb adsorption on the Ag NPs showed the time constant of surface binding t₁?=?5.79 min and 10.23 min and surface reorganization t₂?=?500 min and 251.75 min with the use of small and large concentrations of Ag NPs, respectively. The absorption peak shape and size around the wavelength, λ ≈ 406.2 nm of the bioconjugate has been examined by Gaussian and Lorentz curve fitting analysis. The bioconjugate along with the PC formation has been analyzed by HRTEM images and DLS observations. The tertiary deformation of Hb and energy transfer efficiency connecting Ag NPs and Hb are discussed from the emission-quenching phenomenon. The change of the secondary structural elements (α-helix, β-sheets, intermolecular aggregates, intramolecular aggregates) of the bioconjugate has been analyzed from FTIR spectrum.

     

One-Step Preparation and Fluorescence Enhancement Effect in SiO2/Eu2+ Doped with Ag Nanowires

Eu²⁺ single-doped SiO₂ (SiO₂/Eu²⁺) and Eu²⁺, Ag nanowires co-doped SiO₂ (SiO₂/Eu²⁺–Ag) luminescent nanomaterials were prepared by an efficient one-step sol–gel method. Their microstructure and optical properties were characterized, and the fluorescence enhancement of Eu²⁺ by Ag nanowires was investigated. The experimental results indicate that the average diameter of Ag nanowires doped is 12.5 nm, and the length–diameter ratio is 30. The Ag nanowires cannot only enhance the light absorption of SiO₂/Eu²⁺ in the range of 230–350 nm, but also reduce the fluorescence lifetime of Eu²⁺. More importantly, the emission intensity is enhanced after doping Ag nanowires, and the red shift phenomenon of the emission spectrum is observed, red shift occurs between 10 and 56 nm. The highest fluorescence intensity is accessed under the Ag doping concentration of 0.10 %. Additionally, the emission of SiO₂/Eu²⁺ with 0.10 % of Ag doping at 456 nm is 16 times stronger than that of pure SiO₂/Eu²⁺. The present results indicate that the fluorescence enhancement is attributed to the local field enhancement and the increased radiative decay rates induced by Ag nanowires.     

Dual-Band Plasmonic Enhancement of Ag-NS@SiO2 on Gain Medium??s Spontaneous Emission

We present a theoretical study on plasmonic enhancement of molecular fluorescence near a nanocomposite, Ag nanoshell (Ag-NS) coated by a gain medium of molecule-doped SiO₂ layer. We use an average enhancement factor (AEF), which considers contributions from all possible orientations and locations of molecules in the silica layer to estimate the overall performance of Ag-NS@SiO₂ at specific excitation and emission wavelengths. Our results on the AEF reveal that Ag-NS@SiO₂ is a dual-band enhancer on the spontaneous emission of the gain medium; one is a narrowband in a shorter wavelength regime (quadrupole mode) and the other is a broadband in a longer wavelength regime (dipole mode). These two bands are tunable by adjusting the core size and the thickness of the Ag shell. Due to this merit, Ag-NS@SiO₂ has great potentials to enhance Forster resonance energy transfer between a donor and a corresponding acceptor with large Stokes shifts.     

Supersaturation-Driven Optical Tuning of Ag Nanocomposite Glasses for Photonics: An In Situ Optical Microspectroscopy Study

Silver nanoparticle (NP) precipitation in a melt-quenched aluminophosphate glass matrix has been studied and compared for 8 mol% and 4 mol% concentrations of both Ag₂O and SnO dopants. The assessment is carried out by monitoring the plasmonic evolution of glass-embedded Ag NPs in real time during thermal treatments by in situ optical microspectroscopy and complemented by transmission electron microscopy and X-ray diffraction characterization. The time variation in the surface plasmon resonance of Ag NPs is analyzed in the framework of Mie extinction theory in connection with nanocrystal precipitation in the supersaturated solid solutions. For the higher concentration of silver and tin, nucleation and growth processes were distinguished, which appeared to be temperature- and time-dependent. Hence, favorable conditions were induced for the precipitation of a large amount of small NPs in the system. On the other hand, the nucleation and growth stages were not well separated in time for the lower concentration of dopants, resulting in Ag NPs of a broad size range. However, such less-concentrated nanocomposite allowed for the precipitation of NPs much larger than those observed for the 8% doped glass. Varying the degree of supersaturation in the system has been established as an important means for the tuning of material optical properties for photonic (nanoplasmonic) applications.     

Optical Absorption Modeling of Plasmonic Organic Solar Cells Embedding Silica-Coated Silver Nanospheres

We numerically study plasmonic solar cells in which a square periodic array of core–shell Ag@SiO₂ nanospheres (NSs) are placed on top of the indium tin oxide (ITO) layer using a 3D finite-difference time-domain (FDTD) method. We investigate the influence of various parameters such as the periodicity of the array, the Ag core diameter, the active layer thickness, the shell thickness, and the refractive index of the shell materials on the optical performance of the organic solar cells (OSC). Our results show that the optimal periodicity of the array of NSs is dependent on the size of Ag core NSs in order to maximize optical absorption in the active layer. A very thin active layer (<70 nm) and an ultrathin (<5 nm) SiO₂ shell are needed in order to obtain the highest optical absorption enhancement. Strong electric field localization is observed around the plasmonic core–shell nanoparticles as a result of localized surface plasmon resonance (LSPR) excited by Ag NSs with and without silica shell. Embedding 50 nm Ag NSs with 1-nm-thick SiO₂ shell thickness on top of ITO leads to an enhanced intrinsic optical absorption in a 40-nm-thick poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) active layer by 24.7% relative to that without the NSs. The use of 1-nm-thick ZnO shell instead of SiO₂ leads to an enhanced intrinsic absorption in a 40-nm-thick P3HT:PCBM active layer by 27%.

     

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.

     

Effect of light source on the microbiological desulfurization in a photobioreactor

Removal rates of a toxic pollutant-hydrogen sulfide were investigated using several light sources in photosynthetic desulfurization. An incandescent bulb has a broad spectrum starting from about 400?nm but emits most of its light energy beyond 800?nm as heat. LED₇₁₀ among those sources saved energy considerably comparing with the incandescent light, but the scattering and absorption was a problem in light transmission within the deep region of a bioreactor due to its own weak light intensity. Fluorescent light was inefficient in desulfurization in comparison with light sources illuminating with wide wavelength range, because of the weak transmittance at the peak wavelength of 460?nm. A combination of LED₇₁₀ and fluorescent lamp was estimated as an optimal light source in this study.