Photoinduced Transmission Research Articles

Activity-based molecular CO2 detection by amine-free polymers in organic and aqueous media

Activity-based molecular CO2 detection by amine-free polymers in organic and aqueous media

Photocatalytic fixation of nitrogen to ammonia by NiFe-LDH-derived sulfide microspheres

Direct fixation of nitrogen (N2) to ammonia (NH3) under ambient conditions via photocatalysts is a promising method to relieve the pressure of energy shortage, where chemisorptions of torpid nitrogen and delivery of photoproduced electrons to N≡N bond are recognized technical limitations. In this work, we have developed the catalysts of NiFe-LDH-derived sulfides microspheres ([NiFe]S) with excellent photocatalytic activity for reduction of N2 to NH3. Excitingly, the NH3 generation rates of [NiFe]S catalysts reached up to 111.83 μmol·L−1·h−1 under visible light irradiation in water, which were 10.35 times than that of NiFe-LDH microspheres. The reason was due to the higher photo-induced carrier separation and transmission efficiency of [NiFe]S microspheres. In addition, the possible photocatalytic mechanism was proposed. This new work could guide the design of efficient catalysts and open up the application of metal sulfides in photocatalytic N2 fixation.

Robust sensitizer-assisted platinized titanium dioxide in photocatalytic removal of 4-chlorophenol in water: Light tunable sensitizer

Abstract The photodegradation of 4-chlorophenol (4-CP) by using 3,3′-Pt(dcbpy)(bdt), 33Pt(bdt), sensitized platinized titanium dioxide, Pt-TiO2, under 420 nm light irradiation while bubbling O2 has been studied in this research. The 84% degradation efficiency was reached in 3 h, and this efficiency was much better than that assisted by 4,4′-Pt(dcbpy)(bdt), 44Pt(bdt), under the same conditions using 420 nm light. The possible reason is due to the difference in UV–vis absorption spectra of these two dyes around 420 nm. The 33Pt(bdt) dye which has been first synthesized in this study and has the twisted geometry shows larger open circuit voltage, higher molar extinction coefficient of π–π* transition around 420 nm and much better in 4-CP photodegradation than its 4,4′-analogue under blue light. Under 580 nm light irradiation for 6 h, both 33Pt(bdt) and 44Pt(bdt) sensitized Pt-TiO2-catalyzed 4-CP degradation with O2 bubbling could reach 94% photodegradation efficiency based on metal ligand charge transfer, MLCT, mechanism. Fluorescence quenching experiments have been carried out to affirm the enhanced photo-induced charge separation and transmission during 33Pt(bdt)-assisted reaction. To our knowledge, this is the first time to show that under blue or yellow light irradiation dye-sensitized Pt-TiO2-catalyzed 4-CP degradations have different mechanisms and are tunable by light wavelength. Dye 33Pt(bdt) is more robust and better sensitizer in 4-CP degradation than 44Pt(bdt) under blue light. Thus, by the careful selection of light wavelength and using the robust dye, one can tune the system to efficiently harvest specific visible light for the photodegradation of small organic pollutants.

Multi-particle effects in far-IR optical transmission spectra of Ge/Si quantum dots

Photoinduced and equilibrium optical transmission was studied in undoped and δ-doped Ge/Si quantum dot structures in the far-infrared spectral range. Multi-particle excitations were observed in the absorption spectra of the structures with different doping levels. Photoinduced absorption spectra demonstrate the thermal distribution of the photoexcited holes over the single-particle states of the quantum dot ensemble in contrast with the equilibrium absorption spectra.

Facile Synthesis of Indium Sulfide/Flexible Electrospun Carbon Nanofiber for Enhanced Photocatalytic Efficiency and Its Application.

Heterojunction system has been proved as one of the best architectures for photocatalyst owing to extending specific surface area, expanding spectral response range, and increasing photoinduced charges generation, separation, and transmission, which can provide better light absorption range and higher reaction site. In this paper, Indium Sulfide/Flexible Electrospun Carbon Nanofiber (In2S3/CNF) heterogeneous systems were synthesized by a facile one-pot hydrothermal method. The results from characterizations of SEM, TEM, XRD, Raman, and UV-visible diffuse reflectance spectroscopy displayed that flower-like In2S3 was deposited on the hair-like CNF template, forming a one-dimensional nanofibrous network heterojunction photocatalyst. And the newly prepared In2S3/CNF photocatalysts exhibit greatly enhanced photocatalytic activity compared to pure In2S3. In addition, the formation mechanism of the one-dimensional heterojunction In2S3/CNF photocatalyst is discussed and a promising approach to degrade Rhodamine B (RB) in the photocatalytic process is processed.

Design of Polymer Networks Involving a Photoinduced Electronic Transmission Circuit toward Artificial Photosynthesis.

Many strategies have been explored to achieve artificial photosynthesis utilizing mediums such as liposomes and supramolecules. Because the photochemical reaction is composed of multiple functional molecules, the surrounding microenvironment is expected to be rationally integrated as observed during photosynthesis in chloroplasts. In this study, photoinduced electronic transmission surrounding the microenvironment of Ru(bpy)3(2+) in a polymer network was investigated using poly(N-isopropylacrylamide-co-Ru(bpy)3), poly(acrylamide-co-Ru(bpy)3), and Ru(bpy)3-conjugated microtubules. Photoinduced energy conversion was evaluated by investigating the effects of (i) Ru(bpy)3(2+) immobilization, (ii) polymer type, (iii) thermal energy, and (iv) cross-linking. The microenvironment surrounding copolymerized Ru(bpy)3(2+) in poly(N-isopropylacrylamide) suppressed quenching and had a higher radiative process energy than others. This finding is related to the nonradiative process, i.e., photoinduced H2 generation with significantly higher overall quantum efficiency (13%) than for the bulk solution. We envision that useful molecules will be generated by photoinduced electronic transmission in polymer networks, resulting in the development of a wide range of biomimetic functions with applications for a sustainable society.

Intense terahertz field effects on photoexcited carrier dynamics in gated graphene

We study nonlinear effects of intense terahertz (THz) field on photoexcited carrier dynamics in gated monolayer graphene. By employing optical-pump/intense-THz-probe spectroscopy on lightly doped graphene, we observe a crossover from negative to positive photo-induced THz differential transmission as the THz probe field is increased. We attribute this qualitative change in the response to a crossover from a regime where the photo-induced increase in the carrier density dominates the differential response to one where a THz-field-induced increase in the scattering rate dominates.

AgSbS2 modified ZnO nanotube arrays for photoelectrochemical water splitting

Abstract Large-scale, vertically aligned AgSbS 2 modified ZnO nanotube arrays have been fabricated directly on conducting glass substrates (ITO) via a facile, versatile and low-cost hydrothermal chemical process by using ZnO nanorods as reactive templates. This method is easy to be controlled to develop uniform morphology, and it can be generalized to fabricate other ternary sensitizer nanomaterial for PEC water splitting. In this work, we present a novel ternary sensitizer miargyrite AgSbS 2 for optimized ZnO, and the ZnO/AgSbS 2 nanoarrays film was applied on photoelectrochemical (PEC) photoelectrodes. Strikingly, the photocurrent density of this electrode was up to 5.08 mA cm −2 at 0.096 V versus Ag/AgCl. The excellent PEC properties stems from the enhanced absorption spectrum, high speed of photo-induced charges transmission velocity and appropriate energy gap of coupled nanostructures. Furthermore, this work demonstrates a promising low-cost method for preparing ternary sensitizer modified ZnO nanoarrays as PEC electodes for hydrogen production by water splitting.

Investigation of molecular alignment in poly(methyl methacrylate) polymeric thin films doped with Sudan III chromophore

Abstract Photoinduced molecular alignment in Sudan III/poly(methylmethacrylate) polymeric thin films was investigated using pump-probe method for recording the dynamics of the growing and of the relaxation of photoinduced transmission. Order parameter and dichroic ratio were investigated. Absorption characteristics upon photoinduced molecular alignment were also studied. Results showed that the excitation of Sudan III chromophore molecules by polarized light induces a reversible alignment. It was also noticed that the relationship between the order parameter and the dichroic polarization is linear in both situations of pumping and relaxation phases.

Role of the polymer matrix on the photoluminescence of embedded CdSe quantum dots.

The photoluminescence (PL) of CdSe quantum dots (QDs) that form stable nanocomposites with polymer liquid crystals (LCs) as smectic C hydrogen-bonded homopolymers from a family of poly[4-(n-acryloyloxyalkyloxy)benzoic acids] is reported. The matrix that results from the combination of these units with methoxyphenyl benzoate and cholesterol-containing units has a cholesteric structure. The exciton PL band of QDs in the smectic matrix is redshifted with respect to QDs in solution, whereas a blueshift is observed with the cholesteric matrix. The PL lifetimes and quantum yield in cholesteric nanocomposites are higher than those in smectic ones. This is interpreted in terms of a higher order of the smectic matrix in comparison to the cholesteric one. CdSe QDs in the ordered smectic matrix demonstrate a splitting of the exciton PL band and an enhancement of the photoinduced differential transmission. These results reveal the effects of the structure of polymer LC matrices on the optical properties of embedded QDs, which offer new possibilities for photonic applications of QD-LC polymer nanocomposites.

High-efficiency AgInS(2)-modified ZnO nanotube array photoelectrodes for all-solid-state hybrid solar cells.

Highly ordered AgInS2-modified ZnO nanoarrays were fabricated via a low-cost hydrothermal chemical method, and their application as all-solid-state solar cells was also tested. A sensitizer and a buffer layer were developed around the surface of ZnO nanotubes in the preparation process, and this method is easily be manipulated to produce uniform structure. In this structure, the ZnO served as direct electron transport path, the ZnS as the buffer layer, and the ternary sensitizer AgInS2 as absorber and outer shell. The novel all-solid-state hybrid solar cells (ITO/ZnO/ZnS/AgInS2/P3HT/Pt) showed improved short-circuit current density (Jsc) of 7.5 mA/cm(2), open-circuit voltage (Voc) of 512 mV, giving rise to a power conversion efficiency of 2.11%, which is the relatively highest value ever reported for ZnO-based all-solid-state hybrid solar cells. This better result is attributed to the improved absorption spectrum, high speed of photoinduced charge transmission velocity, and appropriate gradient energy gap structure, which implies a promising application in all-solid-state solar cells.

Effect of Microtubules Hierarchy on Photoinduced Hydrogen Generation and Application to Artificial Photosynthesis

ABSTRACTSeveral strategies have been explored from viewpoint of biomimetics to accomplish artificial photosynthesis by using macromolecules as a medium such as liposomes, supramolecules, and hydrogels.1 Differing from disordered solution systems in which multiple components such as photosensitizer and catalytic nanoparticle are diffusively mixed, the photochemical reactions occur efficiently in medium due to maintenance of the dipersibility of the components and specific molecular arrangement. Here we attempt to clarify the effect of medium hierarchy for photoinduced electronic transmission among multiple components. By conjugating each component on tubulin and integrating them via self-assembly to microtubules, ideal component arrangements with optimum distance for the electronic transmission will be possible.

Synthesis of metastable wurtzite CuInS2 nanocrystals and films from aqueous solution

For the first time, metastable wurtzite CuInS2 nanocrystals and films were successfully synthesized from aqueous solution under atmospheric conditions. The CuInS2 nanocrystals were prepared by stirring and reflux of a metal salt and sodium sulfide in aqueous solution containing thioglycolic acid as a stabilizer. The good absorption in the visible light region may find interesting application in solar cells. The I–V curve indicated that the wurtzite CuInS2 NCs favored the generation of photoinduced carrier and electronic transmission. The proposed synthesis strategy may be used as a general process for the synthesis of hydrophilic chalcogenide semiconductor NCs and is scalable for commercial production with minimal environmental impact.

Broadband absorption bleaching in chirped InGaAs quantum dot semiconductor optical amplifier operating at 1211–1285 nm

Abstract We report on photoinduced absorption bleaching of InAs/InGaAs chirped quantum dot semiconductor optical amplifier (QD SOA) waveguide devices investigated by the traditional femtosecond pump–probe technique applied for a waveguide configuration. To gain broader spectra for the device a chirped QD structure including three groups of quantum dots each dedicated to a ground state transition at wavelength 1285, 1243 and 1211 nm was designed. Photoinduced transmission spectra consisting of ground state transition for the groups of QD’s involved showed coincidence with the electroluminescence spectra and even more exceeded to longer wavelength. From photoinduced transmission kinetics absorption recovery in the range of picoseconds was considered. For comparison a device with typical high photoinduced absorption demonstrating large suppression of absorption bleaching was shown and interpreted.

Unusual observation of fast photodarkening and slow photobleaching in a-GeSe2 thin film

Abstract We report an unusual observation of fast photodarkening and slow photobleaching in a-GeSe 2 thin film, when subjected to 532 nm band gap light illumination. Photobleaching is observed only after complete saturation of photodarkening. A detailed kinetic analysis of photoinduced transmission change reveals that photodarkening is one order faster in comparison to photobleaching. Interestingly, photobleaching has an induction time period and irreversible in nature whereas photodarkening appears to be an instantaneous process with light illumination showing transient characteristics.

Aqueous synthesis and characterization of hydrophilic Cu2ZnSnS4 nanocrystals

In this work, a novel and facile method was developed to synthesize hydrophilic Cu2ZnSnS4 (CZTS) nanocrystals (NCs) for the first time. Hydrophilic CZTS NCs were prepared by stirring appropriate amounts of inorganic metal salt and ammonium sulfide in aqueous solution containing thioglycolic acid as stabilizer at room temperature. The as-prepared hydrophilic CZTS NCs were characterized by XRD, XPS, TEM and UV–vis. The good absorption in the visible light region may find its interesting application in solar cells. I–V curve indicated that the CZTS NCs favored the generation of photoinduced carrier and electronic transmission. The proposed synthesis strategy may be used as a general process for the synthesis of hydrophilic chalcogenide semiconductorNCs.

Conjugated donor–acceptor (D–A) copolymers in inverted organic solar cells – a combined experimental and modelling study

Quantum chemical methods are useful for materials design to improve the performance of organic bulk heterojunction (BHJ) solar cells. However, more integrated studies of quantum chemical modelling and experimental results need to be performed to further improve both the materials design and understanding of the related photo-induced processes and photocurrent generation. In this work we investigated the internal relationship between the molecular structures of four donor–acceptor (D–A) copolymers (P1–P4) and their photovoltaic performances. The effects of the molecular structures on the generation of photo-induced charge carriers, exciton diffusion, dissociation and carrier transmission were compared by combining density functional theory (DFT) calculations of intrinsic geometric, electronic and optical properties with the results of electrochemical, spectroscopic, thermal, AFM and solar cell measurements of the polymers. The quantum chemical methods, which provided a tool to assess the electronic properties and conjugation length in the polymers, highly support the experimental results and therefore the usefulness of quantum chemistry for solar cell materials design.

Optical damage resistance of Ce:Fe:LiNbO3 crystals with various Li/Nb ratios

Ce:Fe:LiNbO 3 crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.94, 1.05, 1.20 and 1.38 in the melt. Their UV–Vis absorption spectra were measured in order to investigate their defect structures and their optical damage resistance was characterized by the photoinduced birefringence change and transmission facual distortion method. The optical damage resistance of Ce:Fe:LiNbO 3 crystals improves with the Li/Nb ratio increases. The dependence of the optical damage resistance on the defect structure of Ce:Fe:LiNbO 3 crystals is discussed in detail.

Probing Ultrafast Carrier Dynamics in Silicon Nanowires

We present the first ultrafast optical pump-probe spectroscopic measurements, to the best of our knowledge, on silicon nanowires (SiNWs). In this study, we performed femtosecond pump-probe measurements on vapor-liquid-solid-grown SiNWs to investigate the influence of the NW diameter, pump and probe polarizations, and pump fluence on the observed dynamics while tuning the probe wavelength below and above the indirect bandgap in Si. For smaller NW diameters, carriers were found to relax more rapidly into both extended and localized states, indicating that a surface-mediated mechanism governs the observed dynamics. The magnitude of the photoinduced transmission change exhibited strong polarization dependence, showing that optical transitions in these quasi-1D systems are highly polarized along the NW axis. Finally, density-dependent experiments revealed that the relaxation time decreases with increasing photoexcited carrier density for an above bandgap probe; however, no significant density-dependent changes in the relaxation dynamics were observed when probed below the bandgap. In short, our experiments reveal the influence of diameter, polarization, and carrier density on carrier dynamics in SiNWs, shedding light on the phenomena that govern carrier relaxation in these important nanosystems and giving insight on their future use in nanophotonic applications.

Plexciton Dynamics: Exciton−Plasmon Coupling in a J-Aggregate−Au Nanoshell Complex Provides a Mechanism for Nonlinearity

Coherently coupled plasmons and excitons give rise to new optical excitations--plexcitons--due to the strong coupling of these two oscillator systems. Time-resolved studies of J-aggregate-Au nanoshell complexes when the nanoshell plasmon and J-aggregate exciton energies are degenerate probe the dynamical behavior of this coupled system. Transient absorption of the interacting plasmon-exciton system is observed, in dramatic contrast to the photoinduced transmission of the pristine J-aggregate. An additional, transient Fano-shaped modulation within the Fano dip is also observable. The behavior of the J-aggregate-Au nanoshell complex is described by a combined one-exciton and two-exciton state model coupled to the nanoshell plasmon.