Well-defined Absorption Bands Research Articles

Absorption and Emission of Chemically and Electrochemically Doped Graphene Nanoribbons

Graphene nanoribbons (GNRs) are narrow stripes of graphene that exhibit unique optical and electronic properties depending on their width and edge type. Recent advances in the bottom-up synthesis of GNRs have enabled precise control over their structure and thus their bandgap. However, the systematic optical and electrical characterization of GNRs obtained from solution-mediated reactions has so far been prevented by the poor stability and processability of GNR dispersions. Here we employ liquid cascade centrifugation (LCC) to obtain size-selected and stable dispersions of bottom-up synthesized 9-aGNRs in toluene and tetrahydrofuran and investigate their intrinsic optical properties. Dispersions and films of these 9-aGNRs show well-defined absorption and photoluminescence bands between 800 and 1000 nm, with relative intensities depending on the LCC-fraction. The best GNR dispersions show photoluminescence quantum yields of up to 70 %. Trions are charged excitons with red-shifted emission that can be created in doped low-dimensional semiconductors, such as carbon nanotubes. Theoretical studies predict large trion binding energies (> 300 meV) in graphene nanoribbons (depending on their width). Hence their optical properties upon doping and possible new features are of interest. Chemical doping of our 9-aGNR dispersions with the strong molecular p-dopant F4-TCNQ and electrochemical doping of GNR thin films in ambipolar electrolyte-gated field-effect transistors results in the expected bleaching of the main absorption bands but also the emergence of new redshifted, charge-induced absorption peaks that may indicate the existence of trions in GNRs.

Reflectance spectra (1–5 μm) at low temperatures and different grain sizes of ammonium-bearing minerals relevant for icy bodies

It has been proposed that ammonium-bearing minerals are present in a varying amount in icy planetary bodies. Their observation at the surface of large objects was related to the upwelling and cryovolcanism of ammoniated water from possible subsurface oceans forming ammonium-bearing minerals (NH4+) mixed with ice at the surface. We analyzed the temperature evolution of the near-infrared spectra of a selected number of anhydrous and hydrated ammonium-bearing minerals containing different anions and water content. Reflectance spectra were collected in the 1–4.8 μm spectral range at cryogenic temperatures ranging from 293 K to ~65 K and the effect of sample's grain size between 32 and 150 μm was also investigated at room temperature. Reflectance spectra of anhydrous samples show well-defined absorption bands in the 1–2.5 μm range. The bands located at ~1.06, 1.3, 1.56, 2.02, and 2.2 μm could be useful to discriminate these salts and their characteristics are examined in detail in this work. On the other hand, the reflectance spectra of water-rich samples show H2O fundamental absorption bands strongly overlapping the NH4+ bands, thus dominating the spectra from 1 to 2.8 μm and fully saturating above 2.8 μm. The position of the absorption bands changes with temperature and grain size, shifting to higher frequencies as temperature decreases. The low-temperature spectra also reveal a fine structure compared to the room temperature ones and display narrower and more defined absorption bands. Granulometry mainly affects the band depth and band area parameters. Moreover, mascagnite, salammoniac, ammonium phosphate, tschermigite, and ammonium nitrate are subjected to a reversible low-temperature phase transition, which is manifested in the spectra by a progressive growth and shift of the bands towards shorter wavelengths with an abrupt change in their depth. This new set of spectra at cryogenic temperatures can be directly compared with remote sensing data to detect the presence of ammonium-bearing minerals on the surface of icy bodies. Their identification can impact our knowledge of the internal composition and dynamics of these bodies as well as their potential habitability.

Neodymium-Doped Multi-Component Borate/Phosphate Glasses for NIR Solid-State Material Applications

Multi-component borate/phosphate glasses doped with 1 mol% Nd2O3 content have been prepared using conventional melt quenching technique to study their physical, optical properties. The physical parameters such as the density, molar volume, ion concentration, polaron radius, inter-ionic distance, and field strength were calculated and compared with other glasses. The density was studied using toluene as immersion liquid and the refractive index of the glass was measured using Abbe’s refractometer. An X-ray diffraction study was carried out to confirm the amorphous structure of the prepared glass samples. The structural properties were discussed using the FTIR spectroscopy results. FTIR data show the functional groups of various glass formers used in the present glass using the beam of infrared radiations. The absorption spectra are used to investigate the optical band gap values and structural disorder observed in synthesized glass samples. UV–Vis absorption spectra of the glass show thirteen significant peaks. Thirteen well-defined absorption bands from UV–VIS absorption spectra show the transition from the ground state (4I3/2) to several excited states of Nd3+. The hypersensitive transition (2G7/2+4G5/2) was positioned around 581 nm. In addition, the Tauc method was employed to evaluate the optical band gap energies of the prepared glasses. Electronic polarizability of the oxide ion and optical basicity of synthesized glasses were calculated using optical band gap and compared with other glass samples. Analysis of Photoluminescence will be studied further.

Efficient UV-visible emission enabled by 532 nm CW excitation in an Ho3+-doped ZBLAN fiber.

Rare-earth-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fibers have evolved to become promising candidates for efficient UV-visible emission because of their low phonon energy and low optical losses, as well as their well-defined absorption bands. We investigate the efficient emission of UV-visible light in a low-concentration (0.1 mol%) Ho3+-doped ZBLAN fiber excited by a 532 nm CW laser. In addition to the direct populating of the thermalized 5F4+5S2 levels by ground-state absorption, the upconversion processes responsible for UV-visible emission from the higher emitting levels, 3P1+3D3, 3K7+5G4, 5G5, and 5F3, of the Ho3+ ions are examined using excited-state absorption. The dependence of UV-visible fluorescence intensity on launched green pump power is experimentally determined, confirming the one-photon and two-photon characters of the observed processes. We theoretically investigate the excitation power dependence of the population density for nine Ho3+ levels based on a rate equation model. This qualitative model has shown a good agreement with the measured power dependence of UV-visible emission. Moreover, the emission cross-sections for blue, green, red, and deep-red light in the visible region are measured using the Füchtbauer-Ladenburg method and corroborated by McCumber theory, and the corresponding gain coefficients are derived. We propose an alternative approach to achieve efficient UV-visible emission in an Ho3+-doped ZBLAN fiber using a cost-effective, high-brightness 532 nm laser.

Modified reverse micelle method as facile way to obtain several gold nanoparticle morphologies

Herein, we report a simple modified methodology based on cationic reverse micelles to form gold nanoparticles (AuNPs) with different morphologies and surface plasmon resonance (SPR) according to the phototherapeutic window (650–850 nm), to be applied in nanomedicine. In this sense, with available and simple changes, it was possible to obtain triangles, rods, spheres, truncated-decahedrons, and rings of gold nanoparticles. These structures were obtained with clear crystallinity changes on the different faces in the same solution, with two well-defined and intense absorption bands, which are interesting and applicable in cancer treatments through photothermic therapy.

The effect of Nd2O3 content on the properties and structure of Nd3+ doped TeO2–MgO–Na2O- glass

Abstract Understanding the influence of rare-earth ions (REIs) in tellurite glass is crucial for the development of efficient solid state laser. In this work, tellurite glasses containing Nd2O3 (0–2.0 mol%) were prepared via melt-quenching method to unveil the effect of different Nd3+composition in the environment of tellurite glass. The prepared glasses were characterized using several techniques to determine their physical, thermal, structural, optical properties and the lasing performance. XRD analysis confirmed the amorphous nature of the proposed glasses. Raman analysis shows that the glass with high content of Nd3+ experienced changes in network structure. Seven well-defined absorption bands from UV–Vis absorption spectra shows the transition from the ground state (4I3/2) to several excited states of Nd3+. The negative bonding parameter proved the ionic character possessed by Nd3+and ligands. The Judd-Ofelt intensity parameters (Ω2, Ω4, Ω6) and radiative properties were determined by Judd-Ofelt theory. The photoluminescence spectra (PL) revealed the lasing potency of the prepared glass in the infrared region at 0.87 μm, 1.06 μm, and 1.30 μm due to efficient emissions from 4F3/2 → 4I9/2, 4F3/2 → 4I11/2, and 4F3/2 → 4I13/2 transition respectively. The glass containing 0.5 mol% of Nd2O3 exhibited high stimulated emission cross-section (3.63 × 10−20 cm2), high quantum efficiency (57.47%), longer decay lifetime (177.61 μs), high optical gain (11.20 × 10−24 cm2) and low saturation intensity Is (2.91 × 108 W/m2) for 4F3/2 → 4I11/2 transition, revealing its suitability for 1.06 μm solid-state laser.

Physical, optical and electrical studies on hybrid Ag NPs/NiSi NWs electrode as a DNA template for biosensor

By means of Chemical Vapor Deposition (CVD), Nickel silicide nanowires (NiSi NWs) were grown on silica substrate followed by a solid-diffusion controlled growth mechanism at different substrate temperatures ranging from 400 to 520 °C. The NWs were then subsequently decorated with Ag nanoparticles (Ag NPs) via a simple thermal evaporation technique. The morphologies of the NiSi NWs and Ag NPs/NiSi NWs showed noticeable dependence on the growth substrate temperatures. NiSi NWs grown at 470 °C exhibited the highest NW density with a uniform decoration of spherical Ag NPs of ~13.7 ± 1.5 nm of diameter. The Ag NPs/NiSi NWs appeared to exhibit a better crystallinity compared to the as-grown NiSi NWs, which could be attributed to metal induced crystallization. Moreover, the decoration of Ag NPs on NiSi NWs showed a significant enhancement in Raman peak intensities mainly in the Ni2Si, NiSi, and NiSi2 phases. The Ag NPs/NiSi NWs demonstrated a well-defined surface plasmon resonance absorption bands centered at around 420 nm, which elucidate the effectiveness of the decoration of Ag NPs on NiSi NW surfaces with a thin amorphous dielectric barrier layer. Using current-voltage (I-V) measurement, Ag NPs/NiSi NWs and NiSi NWs shown to exhibit a surface type Schottky diode with rectifying behavior. The values of ideality factor for the NiSi NWs and Ag NPs/NiSi NWs Schottky diodes were calculated to be 6.992 and 2.559 respectively. Additionally, the values of series resistances were also calculated , where the series resistance obtained are ̃ 91.856 and ̃ 38.697 kΩ for NiSi NWs and Ag NPs/NiSi NWs DNA electrodes, respectively.

Engineering the Slow Photon Effect in Photoactive Nanoporous Anodic Alumina Gradient-Index Filters for Photocatalysis.

In this study, we explore for the first time the capabilities of nanoporous anodic alumina gradient-index filters (NAA-GIFs) functionalized with titanium dioxide (TiO2) photoactive layers to enhance photon-to-electron conversion rates and improve the efficiency of photocatalytic reactions by "slow photon" effect. A set of NAA-GIFs was fabricated by sinusoidal pulse anodization, in which a systematic modification of various anodization parameters (i.e., pore widening time, anodization period, and anodization time) enables the fine-tuning of the photonic stopband (PSB) of these nanoporous photonic crystals (PCs) across the spectral regions. The surface of NAA-GIFs was chemically modified with photoactive layers of TiO2 to create a composite photoactive material with precisely engineered optical properties. The photocatalytic performance of TiO2-functionalized NAA-GIFs was assessed by studying the photodegradation of three model organic dyes (i.e., methyl orange, Rhodamine B, and methylene blue) with well-defined absorption bands across different spectral regions under simulated irradiation conditions. Our study demonstrates that when the edges of characteristic PSB of TiO2-modified NAA-GIFs are completely or partially aligned with the absorption band of the organic dyes, the photodegradation rate is enhanced due to "slow photon" effect. A rational design of the photocatalyst material with respect to the organic dye is demonstrated to be optimal to speed up photocatalytic reactions by an efficient management of photons from high-irradiance spectral regions. This provides new opportunities to develop high-performing photocatalytic materials for efficient photocatalysis with broad applicability.

Yellow emissive carbon dots with quantum yield up to 68.6% from manganese ions

The development of high quantum yield (QY) carbon dots (CDs) is a key requirement for applications. However, how to engineer well-defined absorption band in visible region is a critical challenge to obtaining highly efficient long wavelength emissive CDs. In this work, the strategies of solvent-tuning absorption band and manganese ions-enhancing optical performance are introduced to prepare yellow emissive CDs. The utilization of toluene as solvent is a basis for achieving absorption band at 435 nm and realizing yellow emissive CDs with QY of 46%. Addition of manganese ions increase the degree of conjugated sp2-domians and surface states, further enhancing QY up to 68.6%. Using the yellow emissive CDs, a UV-pumped light-emitting diode (LED) was fabricated based on a 395 nm LED chip. The LED shows warm light with correlated color temperature (CCT) of 1596 K and color purity of 99%. This work provides a new insight for the development of high-quality CDs with versatile properties in pursuit of promising applications.

Optimization of nanocomposite Au/TiO2 thin films towards LSPR optical-sensing

Nanomaterials based on Localized Surface Plasmon Resonance (LSPR) phenomena are revealing to be an important solution for several applications, namely those of optical biosensing. The main reasons are mostly related to their high sensitivity, with label-free detection, and to the simplified optical systems that can be implemented.For the present work, the optical sensing capabilities were tailored by optimizing LSPR absorption bands of nanocomposite Au/TiO2 thin films. These were grown by reactive DC magnetron sputtering. The main deposition parameters changed were the number of Au pellets placed in the Ti target, the deposition time, and DC current applied to the Ti-Au target. Furthermore, the Au NPs clustering, a key feature to have biosensing responses, was induced by several post-deposition in-air annealing treatments at different temperatures, and investigated via SEM analysis. Results showed that the Au/TiO2 thin films with a relatively low thickness (∼100nm), revealing concentrations of Au close to 13 at.%, and annealed at temperatures above 600°C, had the most well-defined LSPR absorption band and thus, the most promising characteristics to be explored as optical sensors. The NPs formation studies revealed an incomplete aggregation at 300 and 500 ⁰C and well-defined spheroidal NPs for higher temperatures. Plasma treatment with Ar led to a gradual blue-shift of the LSPR absorption band, which demonstrates the sensitivity of the films to changes in the dielectric environment surrounding the NPs (essential for optical sensing applications) and the exposure of the Au nanoparticles (crucial for a higher sensitivity).

Water-bearing, high-pressure Ca-silicates

Water-bearing minerals provide fundamental knowledge regarding the water budget of the mantle and are geophysically significant through their influence on the rheological and seismic properties of Earth's interior. Here we investigate the CaO–SiO2–H2O system at 17 GPa and 1773 K, corresponding to mantle transition-zone condition, report new high-pressure (HP) water-bearing Ca-silicates and reveal the structural complexity of these phases. We document the HP polymorph of hartrurite (Ca3SiO5), post-hartrurite, which is tetragonal with space group P4/ncc, a=6.820(5), c=10.243(8) Å, V=476.4(8) Å3, and Z=4, and is isostructural with Sr3SiO5. Post-hartrurite occurs in hydrous and anhydrous forms and coexists with larnite (Ca2SiO4), which we find also has a hydrous counterpart. Si is 4-coordinated in both post-hartrurite and larnite. In their hydrous forms, H substitutes for Si (4H for each Si; hydrogrossular substitution). Fourier transform infrared (FTIR) spectroscopy shows broad hydroxyl absorption bands at ∼3550 cm−1 and at 3500–3550 cm−1 for hydrous post-hartrurite and hydrous larnite, respectively. Hydrous post-hartrurite has a defect composition of Ca2.663Si0.826O5H1.370 (5.84 weight % H2O) according to electron-probe microanalysis (EPMA), and the Si deficiency relative to Ca is also observed in the single-crystal data. Hydrous larnite has average composition of Ca1.924Si0.851O4H0.748 (4.06 weight % H2O) according to EPMA, and it is in agreement with the Si occupancy obtained using X-ray data collected on a single crystal. Superlattice reflections occur in electron-diffraction patterns of the hydrous larnite and could indicate crystallographic ordering of the hydroxyl groups and their associated cation defects. Although textural and EPMA-based compositional evidence suggests that hydrous perovskite may occur in high-Ca-containing (or low silica-activity) systems, the FTIR measurement does not show a well-defined hydroxyl absorption band for this phase, implying the water content, at least in the quenched glass, is below the limit of detection (100–1000 ppm). We conclude that at high pressure, as at ambient pressure, some calcium silicates have a high affinity for H2O and high dehydration temperatures. The thermal stability of these hydrous phases suggests that they could exist along a typical mantle geotherm and thus they might be relevant for understanding the mineralogy and water content of Earth's mantle.

Chiral Imidazolium-Functionalized Au Nanoparticles: Reversible Aggregation and Molecular Recognition.

Gold nanoparticles (AuNPs) stabilized by imidazolium salts derived from amino acids [glycine (1), rac-alanine (2), l-phenylalanine (3), and rac-methionine (4)] were prepared. The AuNPs were stabilized the most by 4, which kept the particles dispersed in water for months at pH > 5.5. These AuNPs exhibited a well-defined absorption band at 517 nm and had an average particle size of 11.21 ± 0.07 nm. The 4-AuNPs were reversibly aggregated by controlling the pH of the solution. Chiral R,R-4-AuNPs and S,S-4-AuNPs were synthesized, and the chiral environment on the nanoparticle surface was confirmed using circular dichroism; these nanoparticles exhibited a molecular recognition of chiral substrates. Furthermore, they showed potential for separating racemic mixtures when supported on a layered double hydroxide.

Enhanced spectrophotometric detection of Hg in water samples by surface plasmon resonance of Au nanoparticles after preconcentration with vortex-assisted liquid-liquid microextraction

This article presents an efficient, simple, and cost-effective method for the determination of trace amounts of Hg by vortex-assisted liquid-liquid microextraction (VALLME) coupled to microvolume UV–Vis spectrophotometry. This method correlates changes in the intensity of localized surface plasmon resonance (LSPR) of tetraoctylammonium bromide (TOABr) coated Au nanoparticles (NPs) after interaction with Hg2+ ion. Spectroscopic measurements of the TOABr-coated Au NPs phase with particular absorption properties (strong and well-defined absorption bands) after analyte extraction by VALLME, provide an accurate and sensitive determination of Hg in water samples, comparable with measurements obtained by atomic absorption spectrometry (AAS). Different variables including sample volume, extraction time, and TOABr-coated Au NPs dispersion volume were carefully studied; final experimental conditions were 5mL, 120μL and 5min respectively. The limit of detection (LOD) was 0.8ngmL−1. The calibration curve was linear at concentrations between the limit of quantification (LOQ) (4.9ngmL−1) and up to at least 120ngmL−1 of Hg. The relative standard deviation for six replicate determinations of 20ngmL−1 of Hg was 4.7%. This method exhibited an excellent analytical performance in terms of selectivity and sensitivity and it was finally applied for Hg determination in spiked tap and mineral water samples.

Supra-(carbon nanodots) with a strong visible to near-infrared absorption band and efficient photothermal conversion.

A novel concept and approach to engineering carbon nanodots (CNDs) were explored to overcome the limited light absorption of CNDs in low-energy spectral regions. In this work, we constructed a novel type of supra-CND by the assembly of surface charge-confined CNDs through possible electrostatic interactions and hydrogen bonding. The resulting supra-CNDs are the first to feature a strong, well-defined absorption band in the visible to near-infrared (NIR) range and to exhibit effective NIR photothermal conversion performance with high photothermal conversion efficiency in excess of 50%.

Structural and optical characteristics of PEDOT/n-Si heterojunction diode

In this work, Poly(3,4-ethylenedioxythiophene), Tetra Methacrylate (PEDOT™) film was deposited by spin coating on glass substrates. Surface topography and crystalline properties of PEDOT™ were carried out by scanning electron microscopy and transmission electron microscopy, respectively. Fourier transform infrared spectroscopy was used for investigating vibrational properties.Optical characteristics were investigated using spectrophotometric measurements in the wavelength range 200–2500nm. Absorption characteristic in the UV region shows a well-defined absorption band. The UV–vis absorption spectrum was resolved by molecular orbital and band theories and the optical transition of the films is allowed and direct. Optical dispersion parameters namely oscillator energy,dispersion energy, lattice dielectric constant and high frequency dielectric constant were determined. Temperature dependent current density–voltage (J–V) characteristics was studied to clarify the dominant charge transport in the temperature range 398–373K. Moreover, temperature dependent of barrier height, ideality factor and series resistance were also considered. The presented results offer a new perspective in optoelectronic applications.

Synthesis, characterization and growth mechanism of β-Ga2O3 nano- and micrometer particles by catalyzed chemical vapor deposition

Monoclinic β-Ga2O3 nano- and micrometer particles were successfully fabricated on Si(111) substrates with NiCl2 as a nucleation agent by chemical vapor deposition. Results demonstrated that the sample comprised monoclinic β-Ga2O3 nano- and micrometer particles with diameters ranging from 0.5 to 1.5 μm. FTIR spectra showed well-defined prominent absorption bands at 455 and 694 cm−1 corresponding to Ga–O vibrations. This result is consistent with that of Raman measurements that the typical Ga–O vibration mode was located at 198 cm−1. Photoluminescence spectrum showed that Ga2O3 nanoparticles had a broad and strong emission band ranging from 300 to 650 nm, which can be attributed to defects such as oxygen vacancies, gallium–oxygen vacancy pairs, and larger surface area of particles. Vapor–solid growth was found to be the mechanism underlying nanoparticle growth, with the nucleation agent Ni2+ ions playing an important role in the formation of particles because defect energies on the substrate surface were changed.

Efficient Synthesis of Low-Profile Angularly-Stable and Polarization-Independent Frequency-Selective Absorbers With a Reflection Band

A fast and efficient synthesis procedure for a new class of low-profile frequency selective electromagnetic absorbers with well-defined absorption and reflection bands as well as steep selectivity between the two is proposed. One contribution of this work lies with the combined use of nonresonant subwavelength capacitive and inductive arrays, which leads to low-profile polarization-insensitive and angularly stable designs. Another novelty stems from the use of rigorous synthesis techniques that enable efficiently selecting the cutoff frequencies, reflectivity level, and skirt selectivity for an arbitrary order of the absorption response. Significantly, here we investigate for the first time the out-of-band characteristics of flat absorbers and demonstrate designs which, at frequencies lower than the absorption band, present high reflectivity with a flat reflection phase. Beyond traditional applications, such as stealth, the combination of a well-defined absorption band with such out-of-band reflection properties makes the proposed frequency-selective absorbers pertinent for dual-band satellite-communication antenna reflectors with congruent beams in transmit and receive bands, where the ratio of 1:1.5 between the two bands is normally required.

Assembly modulation of PDI derivative as a supramolecular fluorescence switching probe for detection of cationic surfactant and metal ions in aqueous media.

We report an amphiphilic perylene diimide (1), a bimolecular analog of l-3,4-dihydroxyphenylalanine (L-DOPA), as a reversible fluorescence switching probe for the detection and sensing of cationic surfactants and Fe(3+)/Cu(2+) in an aqueous media respectively by means of host-guest interactions driven assembly and disassembly of 1. Photophysical studies of 1, going from dimethyl sulfoxide (DMSO) (State-I) to pure aqueous medium (State-II), suggested the formation of self-assembled aggregates by displaying very weak fluorescence emission along with red shifted broad absorption bands. Interestingly, the cationic surfactant cetyltrimethylammonium bromide (CTAB) could disassemble 1 in miceller conditions by restoring bright yellow fluorescence and vibronically well-defined (Franck-Condon progressions A0-0/A0-1 ≈ 1.6) absorption bands of 1 over other neutral and anionic surfactants (State-III). Owing to the metal chelating nature of L-DOPA, 1 was able to sense Fe(3+) and Cu(2+) among a pool of other metal ions by means of fluorescence switching off state, attributed to metal interaction driven assembly of 1 (State-IV). Such metallosupramolecular assemblies were found to reverse back to the fluorescence switching on state using a metal ion chelator, diethylenetriaminepentaacetic acid (DTPA, State-III), further signifying the role of metal ions toward assembly of 1. Formation of assembly and disassembly could be visualized by the diminished and increased yellow emission under green laser light. Further, the assembly-disassembly modulation of 1 has been extensively characterized using infrared (IR), mass spectrometry, microscopy and dynamic light scattering (DLS) techniques. Therefore, modulation of the molecular self-assembly of PDI derivative 1 in aqueous media (assembled state, State-II) by means of host-guest interactions provided by micellar structures of CTAB (disassembled state, State-III), metal ion (Fe(3+) and Cu(2+)) interactions (assembled state, State-IV) and metal ion sequestration using DTPA (disassembled state, State-III) is viewed as a supramolecular reversible fluorescence switching off-on probe for cationic surfactant CTAB and Fe(3+)/Cu(2+).

Photocurrent generation from a low band-gap and green BODIPY-based electrochromic polymer

The electrosynthesis of a low band-gap and neutral-state green linear polymer incorporating a BODIPY core as the acceptor and bis(3,4-ethylenedioxythiophene) (bis-EDOT) as the donor has been described. Resulted polymer exhibited two well-defined absorption bands at 430 and 690nm allowing it to absorb light in the whole visible spectrum. The resulting highly conjugated polymer showed electrochromic behavior and the color changes from neutral-state green to oxidized-state dark blue. The electrogenerated thin film of the polymer displayed good hole mobility in solid state and registered a photo-electrochemical response when light was applied.

Structurally tunable resonant absorption bands in ultrathin broadband plasmonic absorbers

Light absorption is a fundamental optical process playing significantly important role in wide variety of applications ranging from photovoltaics to photothermal therapy. Semiconductors have well-defined absorption bands with low-energy edge dictated by the band gap energy, therefore it is rather challenging to tune the absorption bandwidth of semiconductors. However, resonant absorbers based on plasmonic nanostructures and optical metamaterials emerged as alternative light absorbers due to spectrally selective absorption bands resulting from optical resonances. Recently, a broadband plasmonic absorber design was introduced by Aydin et al. with a reasonably high broadband absorption. Based on that design, here, structurally tunable, broadband absorbers with improved performance are demonstrated. This broadband absorber has a total thickness of 190 nm with 80% average measured absorption (90% simulated absorption) over the entire visible spectrum (400 - 700 nm). Moreover, the effect of the metal and the oxide thicknesses on the absorption spectra are investigated and results indicate that the shorter and the longer band-edge of broadband absorption can be structurally tuned with the metal and the oxide thicknesses, as well as with the resonator size. Detailed numerical simulations shed light on the type of optical resonances that contribute to the broadband absorption response and provide a design guideline for realizing plasmonic absorbers with structurally tunable bandwidths.