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The sun provides a plentiful and inexpensive source of carbon-neutral energy that has yet to be fully utilized. This is a major driving force behind the development of organic photovoltaic (OPV) materials and devices, which are expected to offer benefits such as low cost, flexibility, and widespread availability. For the photovoltaic performance enhancement of the inverted ZnO-nanorods (NR)/organic hybrid solar cells with poly(3-exylthiophene):(6,6)-phenyl-C61-butyric-acid-methylester (P3HT:PCBM) and poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) active layers, gold nanoparticles (Au-NPs) were introduced into the interface between indium-thin-oxide cathode layer and ZnO cathode buffer layer, and the efficiency improvement was observed. It's worth noting that adding Au NPs had both a positive and negative impact on device performance. Au NPs were shown to be advantageous to localized surface plasmon resonance (LSPs) in the coupling of dispersed light from ZnO NRs in order to extend the light's path length in the absorbing medium. Although the light absorption in the active layer could be enhanced, Au NPs might also act as recombination centers within the active layer. To avoid this adverse effect, Au NPs are covered by the ZnO seeded layer to prevent Au NPs from direct contact with the active layer. The dominant surface plasmonic effect of Au NPs increased the photoelectric conversion efficiency from 2.4% to 3.8%.

Owing to the intense carrier recombination and limited optical absorption, the as‐fabricated CsPbBr3 visible light photodetectors (PDs) are far from practical application. In this work, we have demonstrated performance‐improved metal‐semiconductor‐metal (MSM) structured CsPbBr3 visible light PDs realized by the decoration of sputtered Au nanoparticles (NPs). It showed that the Au NPs on the CsPbBr3 exhibited synergistic benefits including improving the photogenerated charge carriers’ lifetime and enhancing the optical absorption of the CsPbBr3, both of which are fundamental factors for the performance‐improved PDs. Electrical characterizations showed that localized Schottky junctions formed at the Au NPs/CsPbBr3 interface. In addition, optical investigations showed that effective resonant coupling occurred between the localized surface plasmon resonance effects of Au NPs and excitons in the CsPbBr3. As a result, the on‐off switching of the Au‐decorated CsPbBr3 photodetector increased by 13 times compared with that of the pristine one. Meanwhile, the peak photo sensitivity of the CsPbBr3 photodetector was increased from 0.088 to 0.61 A W‐1 after the decoration of Au NPs. It is believed that the results shown in this work will provide pathways for fabricating high‐performance CsPbBr3 PDs and other similar devices in the future.

Localized surface plasmon interaction of colloidal gold nanoparticles and the resultant changes in the linewidth of plasmon bands are reported. The evolution of the plasmon band in colloids is investigated by increasing the number of particles per unit volume. The volume of the solvent is reduced from 15 to 3 ml by the simple evaporation method. It is observed that the linewidth of the plasmon band varies in a non-uniform manner, which is attributed to the interaction of plasmons from the surface of gold nanoparticles rather than aggregation effects. Indication of aggregation effects such as a progressive redshift in plasmon peak and continuous broadening of linewidth were absent. Gold nanoparticles are prepared using laser ablation of the gold target with nanosecond laser pulses using pure water as a solvent. Change in the linewidth of plasmon bands on colloidal gold nanoparticles with minimized size distribution prepared using laser fluences viz. 5.09, 10.19, 15.28, 20.38 and 25.48 J/cm2 are explored.

Z-scheme heterojunctions are fundamentally promising yet practically appealing for photocatalytic hydrogen (H2) production owing to the enhanced redox power, spatial separation of charge carriers, and broad-spectrum solar light harvesting. The charge-transfer dynamics at Z-scheme heterojunctions can be accelerated by inserting charge-transfer mediators at the heterojunction interfaces. In this study, we introduce Au nanoparticle mediators in the Z-scheme W18O49/g-C3N4 heterostructure, which enables an improved H2 production rate of 3465 μmol/g·h compared with the direct Z-scheme W18O49/g-C3N4 (1785 μmol/g·h) under 1 sun irradiation. The apparent quantum yields of H2 production with W18O49/Au/g-C3N4 are 3.9% and 9.3% at 420 and 1200 nm, respectively. The improved photocatalytic H2 production activity of W18O49/Au/g-C3N4 is attributable to the triple-channel charge-transfer mechanism: channel I─Z-scheme charge transfer facilitates charge separation and increased redox power of the photoexcited electrons; channels II and III─the localized surface plasmon resonances from Au (channel II) and W18O49 (channel III) enable light harvesting extension from visible to near-infrared wavelengths.

Tunable extraordinary optical transmission (EOT) with graphene is realized using a novel metallic ring–rod nested structure in the terahertz frequency regime. The generated double-enhanced transmission peaks primarily originate from the excitation of localized surface plasmon resonances (LSPRs). On using graphene, the resonating surface plasmon distribution changes in the reaction plane, which disturbs the generation of LSPRs. By regulating the Fermi energy (Ef) of the graphene to reach a certain level, an adjustment from bimodal EOT to unimodal EOT is obtained. As the Ef of the graphene integrated beneath the rod increases to 0.5 eV, the transmittance of the peak at 2.42 THz decreases to 6%. Moreover, the transmission peak at 1.77 THz virtually disappears due to the Ef increasing to 0.7 eV when the graphene is placed beneath the ring. The significant tuning capabilities of the bimodal EOT indicate its promising application prospects in frequency-selective surfaces, communication, filtering, and radar.

Two-dimensional transition metal dichalcogenide (TMDC) nanocrystals (NCs) exhibit unique optical and electrocatalytic properties. However, the growth of uniform and high-quality NCs of monolayer TMDC remains a challenge. Until now, most of them are synthesized via a solution-based hydrothermal process or ultrasonic exfoliation method, in which the capping ligands introduced from organic solution often quench the optical and electrocatalytic properties of TMDC NCs. Moreover, it is difficult to homogeneously disperse the solution-based TMDC NCs on a substrate for device fabrication, since the dispersed NCs can easily aggregate. Here, we put forward a novel CVD method to grow closely spaced MoS2 NCs around 5 nm in lateral size. TEM and AFM characterizations demonstrate the monolayer and high-crystalline nature of MoS2 NCs. An obvious blue-shift with 130 meV in photoluminescence signals can be observed. The MoS2 NCs also show an outstanding surface-enhanced Raman scattering for organic molecules due to their localized surface plasmon and abundant edge sites and exhibit excellent electrocatalytic properties for the hydrogen-evolution reaction with a very low onset potential of ∼50 mV and Tafel slope of ∼57 mV/decade. Finally, we further demonstrate this kind of CVD method as a versatile platform for the growth of other TMDC NCs, such as WSe2 and MoSe2 NCs.

The performance improvement of solid-state triplet-triplet annihilation-based photon upconversion (TTA-UC) systems is required for the application to various solar devices. The performance can be improved by making use of the local strong electric field generated through the excitation of localized surface plasmon (LSP) resonance of metal nanostructures. However, since the improvement is effective only within the limited nanospace around nanoparticles (i.e., the near-field effect), a methodology for improving the performance over a wider spatial region is desirable. In this study, a significant improvement in the threshold light excitation intensity (Ith) (77% decrease) as the figure of merit and the upconverted emission intensity (6.3 times enhancement) in a solid-state TTA-UC film with a thickness of 3 μm was achieved by stacking the film with periodic Ag half-shell arrays. The highest-enhanced upconverted emission was obtained by tuning the diffuse reflectance peak, which results from the excitation of LSP resonance of the Ag half-shell arrays, to overlap well with the photoexcitation peak of the sensitizer in the TTA-UC film. The intensity of the enhanced upconverted emission was independent of the distance between the lower edge of the TTA-UC film and the surface of half-shell arrays in the nanometer order. These results suggest that the performance improvement was attributed to the photoexcitation enhancement of the sensitizer by elongating the excitation light path length inside the TTA-UC film, which was achieved through a strong backward scattering of the incident light based on the LSP resonance excitation (i.e., the far-field effect). In addition, the upconverted emission was improved using half-shell arrays comprising low-cost Al, although the enhancement factor was 3.5, which was lower than that of Ag half-shell arrays. The lower enhancement may be attributed to a decrease in the backward scattering of the excitation light owing to the intrinsic strong interband transition of Al at long visible wavelengths.

Ag loaded Ga2O3 photocatalysts are well known to be highly active for the CO2 reduction with water to CO. However, Ag changes its chemical state during the reaction, resulting in the decrease of its photocatalytic activity. To examine the chemical state change during the photocatalytic CO2 reduction, we have attempted a real time observation of the change in the chemical and physical states of Ag co-catalyst loaded on Ga2O3 by monitoring UV–vis reflectance spectra under the atmosphere simulating the photocatalytic CO2 reduction. In UV–vis spectra, two characteristic absorptions appeared at around 450 nm and 600 nm corresponding to resonance absorptions of localized surface plasmon (LSPR) of Ag nanoparticles (Ag-NPs) and Ag in metallic state. The LSPR absorption appeared as light irradiation started and grew with the time. It was revealed that Ag on Ga2O3 was initially in the oxidized state and reduced by the light irradiation to be Ag-NPs. Further light irradiation enlarged the size of Ag-NPs to be the metallic state especially under atmosphere with water. Under CO2 atmosphere, Ag-NPs remained small after further light irradiation. These results suggest that Ag initially loaded on Ga2O3 in the oxidized state was reduced to be dissolved as Ag+ in water and precipitated as Ag-NPs. Then, some of Ag-NPs aggregated to be larger Ag particles or in the metallic state. Such reduction process depends on gas species of the system, i.e. water promoted the formation of Ag-NPs while CO2 suppressed the formation Ag-NPs.

Degenerately doped metal-oxide nanocrystals (NCs) show localized surface plasmon resonances (LSPRs) that are tunable via their tunable excess charge-carrier densities. Modulation of excess charge carriers has also been used to control magnetism in colloidal doped metal-oxide NCs. The addition of excess delocalized conduction-band (CB) electrons can be achieved through aliovalent doping or by postsynthetic techniques such as electrochemistry or photodoping. Here, we examine the influence of charge-compensating aliovalent dopants on the potentials of excess CB electrons in free-standing colloidal degenerately doped oxide NCs, both experimentally and through modeling. Taking Sn4+:In2O3 (ITO) NCs as a model system, we use spectroelectrochemical techniques to examine differences between aliovalent doping and photodoping. We demonstrate that whereas photodoping introduces excess CB electrons by raising the Fermi level relative to the CB edge, aliovalent impurity substitution introduces excess CB electrons by stabilizing the CB edge relative to an externally defined Fermi level. Significant differences are thus observed electrochemically between spectroscopically similar delocalized CB electrons compensated by aliovalent dopants and those compensated by surface cations (e.g., protons) during photodoping. Theoretical modeling illustrates the very different potentials that arise from charge compensation via aliovalent substitution and surface charge compensation. Spectroelectrochemical titrations allow the ITO NC band-edge stabilization as a function of Sn4+ doping to be quantified. Extremely large capacitances are observed in both In2O3 and ITO NCs, making these NCs attractive for reversible charge-storage applications.

The optical and dielectric properties of plasmonic of Fe2O3/Au and Fe3O4/Au core/shell nanoparticles were studied using Finite Element computational approach. The optical response of these nanostructures was investigated through the computation of the real and the imaginary parts of the effective dielectric permittivity and the absorption cross-section in the visible-near infrared spectral range. Our findings are as follows. Firstly, we have compared our obtained numerical results with those predicted by Maxwell–Garnett effective medium theory. Secondly, the obtained results reveal that the localized surface plasmons resonance (LSPR) peak shifts to near infrared for a Fe2O3/Au-nanoparticle are similar to that of a Fe3O4/Au-nanoparticle having the same geometric parameters. Thirdly, the optical characteristics of the plasmonic nanoparticles were also studied. Finally, we hope that the developed numerical method can be extended to investigate the electromagnetic coupling within or between particles and its effect on the plasmonic behaviors. This makes the core/shell composite nanoparticles extremely interesting for magnetic, optical and biomedical applications.

Recently, localized surface plasmon resonances (SPRs) of metallic nanoparticles (NPs) have been widely used to construct plasmonic nanohybrids for heterogeneous photocatalysis. For example, the combination of plasmonic Au NPs and TiO2 provides pure TiO2 visible-light activity. The SPR effect induces an electric field and consequently enhances light scattering and absorption, favoring the transfer of photon energy to hot carriers for catalytic reactions. Numerous approaches have been dedicated to the improvement of SPR absorption in photocatalysts. Here, we have designed a core@shell-satellite nanohybrid catalyst whereby an Ag NP core, as a plasmonic resonator featuring unique dual functions of strong scattering and near-field enhancement, is encapsulated by SiO2 and TiO2 layers in sequence, with Au NPs on the outer surface, Ag@SiO2@TiO2-Au, for efficient plasmonic photocatalysis. By varying the size and number of Ag NP cores, the Au SPR can be tailored over the visible and near-infrared spectral region to reabsorb the scattered photons. In the presence of the Ag core, the incident light is efficiently confined in the reaction suspension by undergoing multiple scattering, thus leading to an increase of the optical path to the photocatalysis. Moreover, using numerical analysis and experimental verifications, we demonstrate that the Ag core also induces a strong near-field enhancement at the Au-TiO2 interface via SPR coupling with Au. Consequently, the activity of the TiO2-Au plasmonic photocatalyst is significantly enhanced, resulting in a high H2 production rate under visible light. Thus, the design of a single structural unit with strong scattering and field enhancement, induced by a plasmonic resonator, is a highly effective strategy to boost photocatalytic activity.

The extension of plasmonics to materials beyond the conventional noble metals opens up a novel and exciting regime after the inspiring discovery of characteristic localized surface plasmon resonances (LSPRs) in doped semiconductor nanocrystals originating from the collective oscillations of free holes in the valence band. We herein prepare colloidal monodisperse eccentric dual plasmonic noble metal-nonstoichiometric copper chalcogenide (Au@Cu2−xSe) hybrid hetero-nanostructures with precisely controlled semiconductor shell size and two tunable LSPRs in both visible (VIS) and near-infrared (NIR) regions associated with Au and Cu2−xSe, respectively. Through systematic evaluations of the photocatalytic performance of Au@Cu2−xSe upon sole NIR and dual VIS + NIR simultaneous excitations, we are capable of unambiguously elucidating the role of plasmonic coupling between two dissimilar building blocks on the accelerated photocatalytic reactions with greater rate constants from both experimental and computational perspectives. The significantly enhanced strength of the electromagnetic field arising from efficient plasmonic coupling under the excitation of two LSPRs results in the superior activities of dual plasmonic Au@Cu2−xSe in photocatalysis. The new physical and chemical insights gained from this work provide the keystone for the rational design and construction of high-quality dual- or even multi-plasmonic nano-systems with optimized properties for widespread applications ranging from photocatalysis to molecular spectroscopies.

Infrared phototransistors with very high performance show great potential in optoelectronic application, attributable to the intrinsic high transconductive gain of the transistor structure and therefore very large photo-responsivity. To distinguish multispectral information with phototransistors, however, the coincident spectral light has to been laterally dispersed and thereby coupled to the individual photo-gates sensing different target bands. Here, the dual-frequency plasmonic photo-coupler based on a single perforated metallic layer is numerically designed in the infrared region to improve photon absorption efficiency at two target wavelengths. The geometric parameters of the plasmonic grating composed of large and small cross-shaped holes are independently tuned to control the resonance frequencies under different incident (x- and y-) polarization conditions. While the dual-frequency resonant modes are induced by the hybridization between localized surface plasmons (LSPs) and propagating surface plasmons (PSPs), it is found that LSPs play the dominant role and can be effectively adjusted to achieve the target dual-frequency response. More importantly, the spectral response with low- (high-) frequency resonance corresponding to large (small) cross-hole region matches the spatially distributed photogates of the phototransistor structure and therefore realizes near-field enhancement and hence large photoresponsivity at target dual frequencies. In addition, the spectral response for x- and y-polarizations can be unified despite of the apparently broken symmetry between these two polarizations. Our work provides a general strategy to realize sensitive multiband-infrared phototransistors which require only state-of-the-art planar technology and are applicable for highly sensitive infrared photodetection.

In this research, a theoretical and experimental study of bimetallic gold and platinum nanoparticles is reported. From the green synthesis approach, a combination of rongalite with sucrose is used as a reducing and stabilizing agent. Nanoalloys (Au@Pt) and Pt-core/Au-shell nanoparticles were obtained according to the synthesis process used, and the optical response was analyzed. For nanoalloys, two absorption bands were associated with localized surface plasmon resonances. These were located at 300 nm and another between 350 nm and 365 nm, respectively. For core/shell type nanoparticles, an absorption band centered at 530 nm was observed. The images obtained by transmission electronic microscopy (TEM) confirmed the presence of quasi-spherical nanoparticles with core/shell type configurations. Numerical calculations of the cross sections for a Pt-core/Au-shell nanoparticle with spherical geometry was used to establish a comparison with the experimental absorption in the ultraviolet-visible (UV–Vis) spectrum. Complementary, the TEM images and chemical analysis by energy dispersive spectroscopy (EDS) showed the presence of core/shell type nanoparticles.

CuS materials exhibit excellent near infrared (NIR) photoabsorption and photothermal effect, but they are lack of magnetic resonance imaging (MRI) ability. Fe-based nanomaterials possess MRI capacity, but they usually exhibit poor NIR photoabsorption. In order to solve the above problems, we synthesize three kinds of CuxFeySz samples, including FeS2, CuFeS2 and Cu5FeS4 nanomaterials. With the Cu/Fe ratios increase from 0/1.0 to 1.0/1.0 and 5.0/1.0, the localized surface plasmon resonances (LSPRs) characteristic peaks shift to longer wavelength, and the photothermal transduction efficiencies go up from 24.4% to 36.6% and 45.9%. Thus, Cu5FeS4 is found to be the most excellent sample. Especially, Cu5FeS4 exhibits photothermal-enhanced Fenton effect, which can produce hydroxyl radical (·OH) under a wide pH range (e.g., pH = 5.4–7.4) to realize the chemodynamic effect. In addition, Cu5FeS4 can be employed as an efficient MRI contrast agent. When Cu5FeS4 dispersion is intravenously injected into the mouse, the tumor can be detected by MRI as well as thermal imaging, and eliminated through photothermal-enhanced chemodynamic effect. Therefore, Cu5FeS4 can be used as an efficient “one-for-all” type agent for MRI-guided photothermal-enhanced chemodynamic therapy of tumor.

Plasmonic composites consisting of silver nanostructures and zinc oxide semiconductor have better photocatalytic performance than pure zinc oxide. To prepare the composites, nanostructures of zinc oxide particles, gold spheres, and three different silver morphology including cubes, spheres, and wires were synthesized. A detailed study of the main mechanisms governing the activity of plasmonic photocatalysts showed that the improvement of photocatalytic performance is attributed to localized surface plasmon resonance-mediated energy transfer from silver to zinc oxide. This mechanism, which is performed using non-radiative (near-field) and radiation (far-field) processes, led to an increase in the concentration of e−/h+ pairs near the semiconductor. We also showed that the increase of the photocatalytic activity depends on the shape of the silver nanostructures in the composites. Our theoretical and experimental studies have shown that composites containing silver cubes have the highest increase of photocatalytic activity compared to other morphologies. The percentage of photocatalytic degradation of methylene blue solution in presence of silver cubes was about 15% higher than that of other morphologies. Therefore, by controlling the shape of noble metal nanostructures, the photocatalytic activity of a semiconductor can be maximized and adjusted.

Metal-oxides hold promise as superior plasmonic materials in the mid-infrared compared to metals, although their integration over established material technologies still remains challenging. We demonstrate localized surface plasmons in self-assembled, hemispherical CdZnO metal-oxide nanoparticles on GaAs, as a route to enhance the absorption in mid-infrared photodetectors. In this system, two localized surface plasmon modes are identified at 5.3 and 2.7 μm, which yield an enhancement of the light intensity in the underlying GaAs. In the case of the long-wavelength mode the enhancement is as large as 100 near the interface, and persists at depths down to 50 nm. We show numerically that both modes can be coupled to infrared intersubband transitions in GaAs-based multiple quantum wells, yielding an absorbed power gain as high as 5.5, and allowing light absorption at normal incidence. Experimentally, we demonstrate this coupling in a nanoparticle/multiple quantum well structure, where under p-polarization the intersubband absorption is enhanced by a factor of 2.5 and is still observed under s-polarization, forbidden by the usual absorption selection rules. Thus, the integration of CdZnO on GaAs can help improve the figures of merit of quantum well infrared photodetectors, concept that can be extended to other midinfrared detector technologies.

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces.

Silver nanoparticles (Ag NPs) coated by an aqueous emulsion of copolymer were elaborated in a short time using polyol process and microwave (MW) heating. This approach is based on reducing AgNO3 powder in the presence of two main components; ethylene glycol as a dispersed medium and an industrial copolymer (latex) as protecting agent. The structural, morphological and optical properties of the prepared silver nanoparticles have been investigated by UV–Vis spectroscopy, Infrared Spectroscopy (IR), X Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). It was found that all these properties are strongly correlated to the latex copolymer concentration and the MW heating process. The absorption band was determined by UV Visible spectra, showing several bands (localized surface Plasmon band) in the visible region at wavelengths between 410 and 430 nm. The TEM analysis of the obtained products indicates the presence of straight nanowires and dispersed, spherical silver nanoparticles with well-controlled size ranging from 7 to 20 nm. The X Ray Diffraction showed that silver nanoparticles synthesized exhibit face centered cubic (fcc) structure. The infrared spectra show the strong coordination between the surface of silver particles and molecules of latex by O–H and C=O groups. Antimicrobial activity of latex/Ag NPs against E. coli, Staphylococcus aureus, and Pseudomonas aeruginosa has been also demonstrated. The results indicated that latex/AgNPs may damage the structure of bacterial cell membrane.

Developing a simple structure using low-cost material that enables both large-scale fabrication and broadband absorption response is highly desirable but very challenging for achieving high-performance metamaterial absorber. Herein, we propose and numerically investigate an ultra-broadband and wide-angle insensitive perfect metamaterial absorber in the ultraviolet to near-infrared (UV–NIR) region based on a simple metal–dielectric–metal structure. The proposed absorber structure consists of a periodic array of a tungsten hexagonal prism and a tungsten ground plane separated by a silicon dioxide dielectric substrate. The proposed absorber achieves an ultra-broadband absorption response in the range of 275–1000 nm with an absorptivity above 90 $$\%$$ and a relative bandwidth of 106.8 $$\%$$ at normal incidence, which covers from the UV to NIR region. The absorption efficiency is maintained with the figure of merit $$\eta _{OBW}$$ higher than 90 $$\%$$ for a wide incident angle up to 40 $$^{o}$$ for transverse electric (TE) polarization and 65 $$^{o}$$ for transverse magnetic (TM) polarization. The effects of structural parameters and different metallic materials on the absorption performance are presented. In addition, the physical mechanism is analyzed using the surface density and distributions of electric and magnetic fields that are attributed to both localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances. Owing to outstanding merits of simple structure, low cost, and high absorption performance, the designed absorber can be suitable for many applications in the UV–NIR spectrum such as thermal emitters and solar cells.