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Solar photocatalytic hydrogen production is considered as a potential solution to alleviate the current global energy situation. In this work, a novle CdS spherical nanoparticles/Ti3C2 MXene nanosheet (CM) heterostructure photocatalyst was prepared by in situ growth method, which has the characteristics of high efficiency and stability. The results showed that the CM sample has regular morphology and size. When compared with pure CdS, its specific surface area increased and the hydrogen evolution performance also greatly improved. Among them, the hydrogen evolution of CM-0.06 is 1295 μmol·g−1·h−1 (λ > 420 nm), which is 7 times that of spherical CdS, and it also showed stronger stability. Tight interface contact can promote the transfer and migration of photo-generated carriers, and the effective separation of electron hole pairs can enhance the absorption of visible light. In addition, Ti3C2 MXene acts as an electron trap can further accelerate the separation of photogenerated electrons and holes. The synergistic effect between semiconductor CdS and Ti3C2 MXene nanosheets, which provides a new idea for the design of more stable and efficient CdS-based photocatalysts.

AgxSiyOz has the potential to inhibit the recombination of photoinduced electron hole pairs via an internal electric field induced by asymmetrical Si–O tetrahedral chains. The strength of the [SiO4] tetrahedral produces a very strong internal electric field for Ag10Si4O13. Here, a novel and convenient synthetic strategy for nano-Ag10Si4O13 based on a sol-gel method is proposed. A small band gap, an internal electric field and a small size ensure good efficiency for nano-Ag10Si4O13 during all chemical dynamical processes, including charge excitation, charge separation and charge transfer.

A series of BaMoO4 and BaMoO4/BaWO4 phosphors were successfully prepared via a polyacrylamide gel method and low temperature calcination technology. The effects of sintering temperature and mass percentage of BaMoO4/BaWO4 on the phase purity, functional group, surface morphology, charge state, photoluminescence properties and photocatalytic activity of the prepared products were studied in detail. The results indicate that the BaMoO4 phosphor is a scheelite tetragonal structure with high crystallinity. The photoluminescence spectra indicates that the phosphors have a strong blue emission peak at 440 nm with excitation wavelength of 282 nm for the BaMoO4 phosphor, and three emission peaks at 400, 440 and 460 nm with excitation wavelength of 284 nm for the BaMoO4/BaWO4 phosphors. These photoluminescence behaviors can be ascribed to the 1T2→1A1 transition, Jahn–Teller distorted tetrahedral symmetry of [MoO4]2- and surface defect. Photocatalytic experiments further confirmed that the BaMoO4/BaWO4 phosphors exhibit a high recombination rate of electron hole pairs. The result further indicates that the type-I band arrangement structure of BaMoO4/BaWO4 phosphors is beneficial to enhance the photoluminescent properties of single-phase phosphors. This study provides a novel route for preparing the type-I band arrangement structure composite phosphors with high photoluminescent properties and potential applications in light emitting devices, optoelectronic devices, laser devices and white pigments.

Here, we investigate the intrinsic nonradiative recombination mechanism in hematite single crystals that decides the photocarrier lifetime under solar illumination. On the basis of the small polaron theory, we propose that the photogenerated electron-hole pair along with its induced lattice deformation in hematite could be treated as a pseudocoordination-complex (PCC) dispersed in a solid medium. We demonstrate that the nonradiative recombination rate at different temperatures determined from the transient absorption spectroscopy can be excellently described by the nonradiative transition theory developed previously for parallels of the PCC model. Our finding suggests that at room temperature the nonradiative recombination in hematite substantially depends on the probability of quantum tunneling of the nuclear configuration.

Sr-doped NaTaO3 (NTO) single-crystalline films with different Sr compositions of up to 20 mol %, including an NTO film, were first fabricated on LaAlO3(001) substrates by pulsed laser deposition. A...

To achieve the well-dispersed Ni–NiS dual-cocatalysts anchored CdS, the samples have been successfully constructed by a cheap and convenient method of hydroxy acid assisted hydrothermal method. Based on the coordination and reduction effects of hydroxy acids, Ni2+ can be facilely transformed into the high dispersed dual-function sites of Ni0 electrons trap and NiS holes reservoir. The highly dispersed Ni–NiS dual-cocatalysts not only provide more dual-function active sites but also present distinctly enhanced visible light absorption, effectively separated electron hole pairs and quickly migrated charge carriers. The optimized Ni–NiS/CdS–CA presented an excellent photocatalytic H2 generation rate of 57.88 mmol·h−1·g−1, which is about 15.35 times higher than that of NiS/CdS. Moreover, the stability can be distinctly increased by modulating the surface cover of Ni–NiS with a suitable Ni/(Ni + Cd) atomic ratio. This work would provide a unique strategy to design the high effective photocatalysts with high dispersed bi-function dual cocatalysts. The well-dispersed Ni-NiS dual-cocatalysts anchored CdS in situ have been successfully constructed via the coordination and reduction effects of hydroxy acid assisted hydrothermal method. Ni-NiS/CdS-CA not only presents dual-function active sites but also exhibits distinctly enhanced visible light absorption, effectively separated electron hole pairs and quickly migrated charge carriers, resulting in a remarkable enhancement in photocatalytic H2 evolution activity.

In this article, an n-type double-gate low-temperature polysilicon (LTPS) TFT is investigated. Previous work has confirmed that the hot-carrier effect will cause impact ionization. Here we observed that, after hot-carrier stress (HCS), the transfer curve in the saturation region has a negative $\text{V}_{\mathrm {th}}$ shift, and a hump is also observed. The reverse output characteristic shows that gate induced drain leakage (GIDL) of the transistor gradually increases and the subthreshold swing (S.S.) has a tendency to collapse. In structures with longer lightly doped drain (LDD) lengths, the electric field at both source/drain side can be effectively dispersed. Thereby, an extended LDD can reduce the overall degradation, and a physical model of explanation is proposed. By using the energy band diagram, we clarify how the additional electron hole pairs affect the output property. Next, Silvaco TCAD simulation is utilized to illustrate the electric field distribution and validate the physical model.

ZnO nanorods were prepared through a sol-gel process by adding various amounts of water at low temperature and atmospheric pressure conditions for application as a photocatalyst. The 1-D ZnO nanostructures can overcome fast recombination of photogenerated electrons and holes that inhibits photocatalytic efficiency. X-ray diffractometer and transmission electron microscopy measurements confirmed that the (002)/(100) intensity ratio increased from 0.83 to 1.34 and the morphology of the ZnO nanoparticles was changed from a spherical shape to nanorods with the addition of water. UV-vis spectroscopy showed a red shift from 360 nm to 371 nm, which indicates a decrease of the band gap energy. PL measurements of the ZnO nanorods showed a 103 times improvement of the NBE/DLE intensity ratio compared to the ZnO nanospheres. When the photocatalytic efficiency of the ZnO nanoparticles was estimated for the degradation of methylene blue dye under irradiation of UV light, the photocatalytic kinetic constant increased from 0.067 min−1 to 0.481 min−1. As a result, longer ZnO nanorods showed better photocatalytic performance.

Photoexcitation, electron-hole pair migration, charge separation, and current generation are simulated quantum mechanically., Using an innovative quantum mechanical method for an open quantum system, we observe in real time and space the generation, migration, and dissociation of electron-hole pairs, transport of electrons and holes, and current emergence in an organic photovoltaic cell. Ehrenfest dynamics is used to study photoexcitation of thiophene:fullerene stacks coupled with a time-dependent density functional tight-binding method. Our results display the generation of an electron-hole pair in the donor and its subsequent migration to the donor-acceptor interface. At the interface, electrons transfer from the lowest unoccupied molecular orbitals (LUMOs) of thiophenes to the second LUMOs of fullerene. Further migration of electrons and holes leads to the emergence of current. These findings support previous experimental evidence of coherent couplings between electronic and vibrational degrees of freedom and are expected to stimulate further work toward exploring the interplay between electron-hole pair (exciton) binding and vibronic coupling for charge separation and transport.

The properties of electron–hole (e–h) pairs generated in a working poly(3-hexylthiophene) (P3HT) diode are investigated by electrically detected magnetic resonance (EDMR) techniques. The EDMR intensity is shown to increase with increasing density of injected electrons for a given hole density, demonstrating that the EDMR signal arises from an e–h pair. The EDMR spectrum consists of two Gaussian curves, one of which gives a g-value very similar to that of hole carriers, suggesting that the EDMR spectrum is given by the sum of electron spin resonance (ESR) spectra from hole and electron carriers forming e–h pairs. Bias-dependent correlation between carriers and e–h pairs under diode operation is examined directly from independent measurements of near-infrared (NIR) spectroscopy for carriers and EDMR for e–h pairs. When the bias is increased to above a threshold, the EDMR signal is strongly reduced despite a gradual increase in the NIR signals, providing evidence that the e–h pairs are dissociated by an elec...

The electronic structures and optical properties of La, C-codoped TiO2 were investigated by the first-principles plane-wave ultrasoft pseudopotential method. Our calculations suggest that the micro-structures of La-C codoped system is different from that of TiO2, and the hole effective mass is increased by La-doping, which can create holes in the valence band; Nonmetal C doping can narrow the band gap of TiO2 and enhance the photo-catalytic activity by the formation of localized mid-gap state originated from C 2p states above the top of the valence band; Metal La and nonmetal C co-doping could induce a synergistic effect, the doping of La atoms leads the redistribution of C 2p states in C atoms, which provide more electrons to participate into the 3d states of Ti atoms. The charge compensation effects between Ti 3d and C 2p produce impurity levels, which reduce the band gaps and enhance the carrier concentration, meanwhile La ions are not easy to enter the lattice of TiO2, which may form hetero-junction structure of La2O3-TiO2 with better dispersion in the bulk phase of TiO2 to limit the recombination of photo-generated electron hole pairs. The calculated results of optical properties show that C-TiO2 and La-C-TiO2 systems exhibit good visible absorption and the doping is beneficial to the propagation of light in the doped TiO2.

The ablation of a target, composed of a homogeneous mixture of Fe & Co metal with H3BO3 powder, produces core-shell type particles on the as-deposited coating surface. Annealing at 600 °C in air transforms the core-shell into urchin-like particles having nanowires of 10–30 nm in diameter and 0.5–1 μm in length, grown radially from the particle surface as a result of the stress created between core and shell. Microstructural and analytical characterization confirms that nanowires are composed of CoFe2O4 and CoO phases forming a heterojunction, which showed outstanding performance as a photocatalyst, requiring half the time for an organic water pollutant degradation reaction in comparison to similarly nanostructured single-metal oxide counterparts (Co3O4 and Fe2O3). Degradation reactions conducted in controlled conditions demonstrate that the urchin-like mixed oxide coatings are highly efficient both in direct photocatalysis and in photo-Fenton reaction. This overall enhancement in activity is due to a synergistic effect created at the heterojunction of CoFe2O4/CoO that allows the formation of a Z-scheme mechanism to facilitate the spatial separation of photoinduced electron-hole pairs. Moreover, the hierarchical urchin-like nanostructures provide a large number of active sites for photocatalytic reactions, while the lower band gap of CoFe2O4 permits better visible light absorption to effectively degrade organic pollutants even under visible light. Based on all the results, a plausible reaction mechanism is proposed related to Z-scheme heterojunction formed with CoFe2O4/CoO.

Recombination of the carrier due to the surface state level traps could affect betavoltaic performance. Herein, we employed a theoretical 1-D carrier transport calculation to investigate the surface passivation effect in a planar [147Pm]-Si p-n junction betavoltaic cell and the results were verified using previous studies. In comparison to the ideal condition of the passivated surface, we predict a 10.74% power loss at the device, thus further research concerning the surface passivation layer for betavoltaic batteries might be necessary.

Graphitic carbon nitride (g-C3N4) is an analog to the graphite in the materials science for its unique electronic structure. The g-C3N4 materials are having enormous assurance on photocatalytic applications but, pure g-C3N4 suffers from major drawbacks which includes poor disparity, low surface area as well as high recombination rate of photo generated electron hole pairs which greatly reduces its photocatalytic activity. Advantageously, high chemical and thermal stability give opportunity to amend g-C3N4 with other samples to conquer aforementioned limitations. Furthermore, it was proved that coupling with co-catalysts over pristine g-C3N4 could significantly develop its photocatalytic performance through synergistic effects of the incorporated semiconductors. This review gives an outline the recent progress in the improvement of g-C3N4 based ternary composite (CNT). Various methods utilized to prepare the g-C3N4 based ternary composite photocatalyst including with their corresponding examples were explained. Also, this review article discussed the g-C3N4 based ternary composite photocatalytic applications in the O2 evaluation, H2 production and CO2 reduction and photocatalytic degradation of organic dyes in aqueous solution.

The accumulation of contaminants on the electrical devices could adversely affect the operation. The present work used photocatalytic functional material to coat on the surface of the electrical devices to prevent the influence of organic contamination. This kind of material was mainly composed of TiO 2 that can remove the contamination by the effect of photooxidation. The photocatalysis was affected by the strength of UV light and electric field. In the experiment, methyl orange (MO) was used as the organic contaminant. The effect of UV light and auxiliary electric field were analysed based on the theoretical simulation. With the stronger UV light, more electron–hole pairs were generated, photocatalytic effect became more pronounced. With the auxiliary electric field, the recombination of electron and hole could be restrained that would increase the productive rate of hole; therefore, more hydroxyl radical will be produced to degrade MO.

Photocatalytic nitrogen fixation provides an attractive approach to produce reactive nitrogen compounds at benign conditions. Herein, Ag decorated δ-Bi2O3 photocatalyst, which has the features of multilayer ultrathin structure, suitable absorption edge and many exposed surface sites, is prepared by a hydrothermal and photoreduction process. Under visible light illustration, the obtained Ag-δ-Bi2O3 photocatalyst exhibits efficient photocatalytic activity for NH4+ generation at room temperature and atmospheric pressure in aqueous solution. The multilayer ultrathin sheets in the structure of Ag-δ-Bi2O3 favors the effective separation of photogenerated electron-hole pairs and fast interfacial charge transfer. Due to the Ag surface plasmonic resonance, obvious trap is formed in the ultrathin Ag-δ-Bi2O3 sheets, which not only inhibites the recombination of electron hole pairs but also produces light-induced oxygen vacancies under irradiation. Those factors significantly improve the photocatalytic ability of as-prepared Ag-δ-Bi2O3. The results provide insights into rational design of enhanced active photocatlysts with Ag surface plasmonic resonance and ultrafast charge carrier transfer for photocatalytic nitrogen fixation.

In this paper, a new magnetic photocatalyst MnxZn1-xFe2O4/α-Bi2O3 is synthesized by the dip-calcination technology, using manganese zinc ferrite as a magnetic substrate. It is beneficial to separate the composite from liquid solution under an extra magnetic field. This heterojunction of composite MnxZn1-xFe2O4/α-Bi2O3 presents remarkable photocatalytic activity and prominent photocatalysis for degradation of Rhodamine B (RhB), far exceeding the pure α-Bi2O3. Especially, the introduction of MnxZn1-xFe2O4 not only reduces the bandgap of photocatalyst α-Bi2O3, but also improves its response in the visible region. Importantly, the magnetic photocatalyst is capable of being used repeatedly, and the photocatalytic activity would remain above 90% after 3 cycles. Such an outstanding stability and retrievability of composite are mainly ascribed to the soft-magnetic material MnxZn1-xFe2O4, enhancing separation of photoinduced electron hole pairs. This work will replace the traditional semiconductor photocat...

Stationary waves in the condensate of electron-hole pairs in the $n\ensuremath{-}p$ bilayer system are studied. The system demonstrates the transition from a uniform (superfluid) to a nonuniform (supersolid) state. The precursor of this transition is the appearance of the roton-type minimum in the collective mode spectrum. Stationary waves occur in the flow of the condensate past an obstacle. It is shown that the roton-type minimum manifests itself in a rather complicated stationary wave pattern, with several families of crests which cross one another. It is found that the stationary wave pattern is essentially modified under variation in the density of the condensate and under variation in the flow velocity. It is shown that the pattern is formed in the main part by short-wave modes in the case of a point obstacle. The contribution of long-wave modes is clearly visible in the case of a weak extended obstacle, where the stationary wave pattern resembles the ship wave pattern.

Low lattice thermal conductivity (κL) is desirable for advancing thermoelectric (TE) materials and devices. However, κL depends on many factors such as phonon scattering sources, electron-phonon interactions, etc. It remains not fully understood how κL is influenced by excited electron-hole (e-h) pairs ubiquitously present in thermoelectrics. To address this issue, the constrained density functional theory (CDFT) simulations are performed to investigate the phonon transport properties of two typical TE materials, Mg2Si and PbTe. Surprisingly, at high e-h concentrations of ∼1021 cm-3, the κL of Mg2Si is reduced significantly by ∼30% due to the softening phonon modes. In contrast, the κL of PbTe first decreases by ∼18% at a relatively low e-h concentration of 2.34 × 1020 cm-3, but it is enhanced by ∼3.4% as the carrier concentration increases to 7.02 × 1020 cm-3. The different behaviors of these two materials arise from the different distributions of excess electrons and holes under e-h excitation. The simulation results suggest that controlling e-h pairs may offer a promising approach to design high-performance TE devices.

Construction of heterojunction is an effective way to improve the photocatalytic activity of photocatalyst. In this work, a simple precipitation method was adopted to anchor rod-like AgVO3 on Bi4Ti3O12 nanosheets to form heterojunction. The results show that Ag can act as an electronic medium to construct Z-scheme heterojunctions, that more visible light can be absorbed and facilitates the separation of electron hole pairs compared with the pure Bi4Ti3O12. The AgVO3/Bi4Ti3O12 composites displayed superior photocatalytic photodegradation of tetracycline (TC) under visible irradiation (λ > 420 nm). 12%AgVO3/Bi4Ti3O12 (AgVO3 with the mass ratio of AgVO3/Bi4Ti3O12 = 12%) showed the highest photocatalytic degradation efficiency, 57% of TC was degraded within 60 min which was the 9.5 times and 2.5 times higher than pure AgVO3 and Bi4Ti3O12. The capture experiment results showed that ·O2− and h+ are the main active radicals in the process of TC degradation. The improved photocatalytic activity is attributed to the construction of Z-scheme heterojunction, which leads to expand the light absorption range and efficient separation of photogenerated carriers. In addition, the mechanism of the photocatalytic degradation of antibiotics was proposed.

Piezo-photocatalysis (implement by ultrasound vibration and UV-vis light irradiation), a new-emerging strategy, can suppress the rapid recombination of electrons and holes to enhance the catalytic performance. The modulation of interface structures (e.g., the introduction of oxygen vacancies, OVs) plays a significant role in the charge-transfer and the catalytic activity. In this paper, the AgNbO3 (ANO) powder was prepared by a facile hydrothermal method. Based on this, we introduce OVs into ANO successfully by annealing in N2 (ANO-N2). The ANO-N2 with OVs exhibits much better piezo-photocatalytic activity for degradation of Rhodamine B (RhB) than the ANO. The result found that OVs can narrow the band gap and improve the UV-vis light absorption, and most importantly, promote the separation of electron hole pairs under electric field to enhance the piezo-photocatalytic performance. The work thus supplies an in-depth understanding of the mechanism between OVs and piezo-photocatalytic performance.

Designing efficient visible light photocatalysts is targeted to improve the solar utilization to ameliorate environmental problems. Ag10Si4O13 has great application potential due to a narrow band gap and the existence of internal electric field（spontaneous polarization electric field inside the crystal）. Here, a novel and convenient synthetic strategy based on sol-gel method and template method was proposed to fabricate 3D sponge-like hierarchical pore Ag10Si4O13 (HPA) microblock with enhanced photocatalytic activities. The group multiple coordination is conducive to further improve the dispersion of Ag10Si4O13 precursor around polystyrene (PS) microsphere. Weak sintering between nano-Ag10Si4O13 particles ensured the formation of sponge skeleton structure. Compared with Ag10Si4O13, HPA showed enhanced separation efficiency of electron hole pairs due to the carbon doping. And the uniform and well-developed pore structures further improved the photocatalytic performance. As a result, HPA (P-5) exhibited a degradation efficiency of 98.98% at 30 min under visible light, and an excellent cycle performance were obtained. The proposed strategy provides an important reference for the preparation of easily recoverable microblock photocatalyst.

The demand for low-cost high efficient photoelectronic devices tends to drive the present need for investigations on advanced multi-functional semiconducting nanostructures. In this regard, the physico-chemical traits of sonochemically processed ZnTe nanostructures and hydrothermally grown ZnO nanostructures were studied using Raman, UV–vis absorbance, X-ray photoelectron spectroscopy and high resolution microscopic tools. The p-n ZnTe/ZnO heterojunctions were then fabricated via spin casting a colloidal ZnTe suspension on periodically aligned ZnO nanowires and investigated for their photoelectronic functionalities. The current-voltage (I-V) characteristics revealed an obvious rectifying behaviour with the forward current and rectification ratio getting improved on lowering the threshold voltages. The series resistance of the diodes were additionally studied using the dV/dlnI derivate plots. The stability of the diodes were also affirmed using their time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the interface. Finally, the ZnTe/ZnO heterojunction behaviour was assimilated using the electrochemical impedance spectroscopic (EIS) results that were studied individually for ZnTe and ZnO nanostructures and collectively across ZnTe/ZnO heterostructure.

In this research, we did not use any template, but a prickly structure urchin like morphology made of composite TiO 2 /g-C 3 N 4 was synthesized by a one-step solvothermal method. It is generally reported that TiO 2 is a pure phase, besides, the photocatalytic effect of multiphase TiO 2 will be better. After the g-C 3 N 4 was successfully loaded on the TiO 2 surface, the morphology did not change. The special sea urchin morphology provides more active sites for catalysis. The band gap becomes smaller, because two materials were combined to form an interface effect. Meanwhile, it could effectively separate electron hole pairs, and promote charge transfer efficiency. More active substances were produced under visible light, such as superoxide radicals and holes. The scavenging experiment further confirms that superoxide radicals and holes play an important role in the catalytic process. The photocatalytic degradation of ibuprofen under visible light was improved. A possible enhanced photocatalytic mechanism of g-C 3 N 4 /TiO 2 heterojunction photocatalysts was proposed.

Intriguing intrinsic properties of light quanta and related topics are reviewed by emphasizing the self-consistency of light-matter interactions and open nano-systems dynamics. It is pointed out that there still remain fundamental and challenging issues related to quantization of a finite nano-system interacting with a massive (i.e., localized) photon field,as well as with a hierarchical or structured phonon field. By using theoretical frameworks developed for an infinite system, some of quantum nature of a finite nano-system are revealed, and it is theoretically shown that dynamic phonon environments and the interplay of coherent and incoherent phonons play an important role in quantum coherent dynamics of electron-hole pairs interacting with massive photon fields.

Phosphorus (P) and boron (B) co-doped Si nanocrystals (NCs) have raised interest in the optoelectronic industry due to their electronic tunability, optimal carrier multiplication properties, and straightforward dispersibility in polar solvents. Yet a basic understanding of the interaction of photoexcited electron–hole (e–h) pairs with new physical features that are introduced by the co-doping process (free carriers, defect states, and surface chemistry) is missing. Here, we present the first study of the ultrafast carrier dynamics in SiO2-embedded P–B co-doped Si NC ensembles using induced absorption spectroscopy through a two-step approach. First, the induced absorption data show that the large fraction of the dopants residing on the NC surface slows down carrier relaxation dynamics within the first 20 ps relative to intrinsic (undoped) Si NCs, which we interpret as enhanced surface passivation. On longer time-scales (picosecond to nanosecond regime), we observe a speeding up of the carrier relaxation dynamics and ascribe it to doping-induced trap states. This argument is deduced from the second part of the study, where we investigate multiexciton interactions. From a stochastic modeling approach we show that localized carriers, which are introduced by the P or B dopants, have minor electronic interactions with the photoexcited e–h pairs. This is understood in light of the strong localization of the introduced carriers on their original P- or B-dopant atoms, due to the strong quantum confinement regime in these relatively small NCs (

Bismuth-based nanomaterials exhibiting unique structures, which endow them with fascinating physicochemical properties, have received more and more interests as promising photocatalysts. Fabrication of BiOIO 3 photocatalysts by calcination method was investigated for the first time. XRD patterns showed that the crystallinity of BiOIO 3 photocatalysts could be controlled by calcination temperature. TGA demonstrated that calcining the precursor at a specific temperature range was appropriate for preparing BiOIO 3 photocatalysts. XPS and FT-IR characterization revealed that the BiOIO 3 photocatalysts prepared by calcination method possessed oxygen vacancies, which acted as the positive charge centers to trap the electron easily, inhibiting the recombination of photo electron-hole pairs. Furthermore, PL spectra confirmed the oxygen vacancies can favor for the separation of the electron-hole pairs and in turn enhance the photocatalytic performance. From the above analysis, the mechanism of preparing BiOIO 3 photocatalysts by calcination method was proposed. Meanwhile, the effect of oxygen vacancies on the photocatalytic activity of BiOIO 3 photocatalysts was investigated. The BiOIO 3 photocatalysts with oxygen vacancies were found to be efficiently photocatalytically remove gaseous Hg 0 and the relative photocatalysis mechanism was investigated.

Graphene model with a high-energy k · p-Hamiltonian has been proposed. A feature of the model is the increasing spin-orbital coupling at relativistic exchange interactions of electron-hole pairs. Topological nontriviality of the model has been established by non-abelian Zak phase calculations. It has been shown that the homotopy group of the model is Z2 × Z4.

The preparation of vertical heterojunction structures using low dimensional films combined with strong light-absorption bulk material has dramatically accelerated the development of next-generation photovoltaic systems. Among the transition metal dichalcogenides, molybdenum disulfide (MoS2) exhibits enormous potential for light-matter interactions and band nesting in photovoltaic devices, improving the absorption of photons and the generation of electron hole pairs. Unfortunately, the lateral scale of MoS2 prepared by traditional methods is in the order of a few micrometers, which severely limits its industrial application. In this work, a novel method to synthesize MoS2 monolayers on a large scale by directly sulfurizing molybdenum foil is presented. This method allows precise control of the layer number as well as the nondestructive transference of MoS2 monolayers on various substrates. In this work, MoS2 monolayers with optimized layer numbers are inserted at the graphene/n-Si interface and function as photon absorption and interfacial band engineering layers. This dramatically enhances the photovoltaic conversion efficiency of Schottky junction solar cells based on graphene. Finally, relatively high conversion efficiency of ~12% is successfully achieved in the heterojunction solar cells based on 2D materials. This work provides a promising new approach to obtaining 2D materials on a large scale, with potential for application in next-generation photovoltaic devices.

Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar Eg and Efb values of 1.93±0.04 eV and 0.48±0.06 eV respectively. Eonset of 0.48±0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm-2 at 0 V vs RHE of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for the bare Cu2O photocathodes. Although different deposition methods show a similar average photocurrent density 2.8±0.3 mA/cm2 at 0 V vs RHE, large variations in the photocurrent density are observed for samples prepared under nominally identical deposition methods.

Bismuth as an element of group VA (P, As, Sb, Bi), which is considered as beyond graphene materials, has attracted much attention because of its stable topological insulator properties. Herein, photoelectrochemical (PEC)-type photodetector based on two-dimensional bismuth nanosheets was designed and fabricated. By using a solid electrolyte to replace the traditional electrolyte, we have achieved a novel structure to make the device more portable. Besides that, due to the solid/liquid heterojunction, which generates an built-in electric field that can separate electron hole pairs effectively, this type of photodetector possess self-powered ability, and it exhibited preferable photoresponsivity which is about 0.5 μA W−1 without external bias potential; meanwhile, the rise time of the photodetector is about 3.3 s and decay time is about 1.8 s. Moreover, we used the flexible indium-tin oxide (ITO) as the substrate; the prepared device can work under the bending states. The novel structure and the excellent properties of the fabricated self-powered flexible PEC-type photodetector make it more promising in the optical detection field.

In this work, ZnO/rGO nanocomposites (NCs) were synthesized through a low temperature sol–gel method. Zinc oxide decorated on graphene sheets could provide surface enhancement and hinder the rapid recombination rate of electron hole pairs that occur during a photocatalysis process. It has been observed that the loading of ZnO decorated on graphene sheets is important in controlling the morphologies and surface enhancement of ZnO/rGO NCs. Field Emission Scanning Electron Microscope (FESEM) micrographs reveal that spherical shape and hexagonal-based nanopyramid of ZnO can be formed at low and high loading of ZnO, respectively. NCs showed excellent performance for degradation of perfluorooctanoic acid (PFOA) and methyl orange in aqueous solution under solar irradiation. Herein, mechanisms for the formation of different shapes of ZnO nanostructures decorated on graphene and their enhancement towards surface and photoactivity were discussed in details.

CoWO4/PbWO4 nanocomposites were successfully synthesized at room temperature (RT) by co-precipitation route without using any templates or surfactants and sintered at 600 °C for good crystallization. The sintered samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy and Zeta potential measurements. UV–Visible diffuse reflectance spectroscopy, photoluminescence (PL) and PL lifetime were studied at RT. The results indicate that the composites have two-phase composition: CoWO4 and PbWO4. SEM micrograph and zeta potential measurements reveal particle agglomeration. The intrinsic PL peak emission at 467 nm of CoWO4 nano sample was enhanced upto four times by optimizing the atomic ratio of Pb/Co concentration. The interconnected interface of CoWO4/PbWO4 nanocomposites could have led to increase in number of recombination of electron hole pairs in CoWO4 and enhanced its intrinsic PL emission intensity. The mechanism of enhanced PL emission for the CoWO4/PbWO4 nanocomposites can be attributed to charge transfer between [WO4]2− and [WO6]6− complexes due to intra particle agglomeration leading to possible interface.

Delocalization of charge carriers through formation of native defects in NiO, to achieve a good metal oxide hole transport layer was attemted in this work and thus a heterojunction of p-type NiO and n-type FTO have been prepared through sol-gel process on FTO coated glass substrate. The synthesis process was stimulated by imparting large number of OH− sites during nucleation of Ni(OH)2 on FTO, so that during oxidation through annealing Ni vacancies are introduced. The structural properties as observed from X-ray diffraction measurement indicate formation of well crystalline NiO nanoparticles. Uniform distribution of NiO nanoparticles has been observed in the images obtained from scanning electron microscope. The occurrence of p-type conductivity in the NiO film was stimulated through the formation of delocalized defect carriers originated from crystal defects like vacancies or interstitials in the lattice. Ni vacancy creates shallow levels with respect to the valance band maxima and they readily produce holes. Thus a native p-type conductivity of NiO originates from Ni vacancies. NiO was thus obtained as an auspicious hole transport medium, which creates an expedient heterojunction at the interface with FTO. Excellent rectifying behavior was observed in the electrical J–V plot obtained from the prepared heterojunction. The results are explained from the band energy diagram of the NiO/FTO heterojunction. Remarkable photoresponse has been observed in the reverse characteristics of the heterojunction caused by photon generated electron hole pairs.

Organic semiconductors possess low dielectric property which indeed constrains their applications in organic electronic devices, such as organic photovoltaics. Here, we report an optically tunable magneto-capacitive response from NPB based organic electronic devices at excited states. The devices exhibit some remarkable magneto-capacitance phenomena at room temperature due to the spin-dependent dissociation and charge accumulation at PMMA/NPB interfaces. With two different preparation methods for the NPB layers, such as the thermal evaporation and solution methods, we have found the line-shape of the magneto-capacitance can be significantly changed, and the line-shape narrowing is more favorable for the devices based on the solution method. We have proposed that the effect is due to the formation of some large aggregates, and it eventually leads to the decrease of the spin exchange interaction within intermolecular electron-hole pairs.

Heterostructured mixed oxide BiVO4-ZnO is used as semiconductive photocatalyst for the degradation of simulated wastewater from tannery industry in the presence of sun light at neutral pH by semiconductive photocatalysis. The mixed oxide catalyst showed higher degrading efficiency in comparison to bare ZnO and bare BiVO4 metal oxides. Analysis of FESEM and AFM images reveals that particles are in the range of 40 nm and mixed oxide catalyst exhibit uniform porous structure respectively. The crystallinity and planes of the catalysts were studied by XRD analysis. The optical band gap of the mixed oxide catalyst (3.02 eV) was examination by UV–Vis diffuse reflectance spectroscopy. The higher catalytic activity with BiVO4-ZnO is attributed to the change in charge carrier equilibrium at the interface of mixed oxide catalyst, which in turn reduces the recombination rate of electron hole pairs and also decreases the energy gap suitable for degradation in solar light. Under the optimal experimental conditions, 64% reduction in COD has been observed with heterostructured BiVO4-ZnO catalyst in six hours of reaction in the presence of sun light.

It is generally believed that electrons and holes in organic solar cells are generated by dissociation of excitons at the interface between donor and acceptor materials in the form of geminate, coulombically bound electron-hole pairs. The further motions of electrons and holes are restricted to the acceptor material and donor material, respectively. Using the method of prescribed diffusion, we solve the Smoluchowski equation describing evolution of the spatial distribution of electrons and holes. The separation probability of electron-hole pairs is found as a function of an initial intrapair separation and external electric field.

Single junction solar cells were fabricated with intrinsic hydrogenated amorphous silicon germanium (a-SiGe:H) as the active layer, that shows a 10% photovoltaic conversion efficiency. The a-SiGe:H active layer of the solar cells of type-A had constant band gap materials while that of type-B had a four step graded band gap by composition gradient (CG). The cells with composition gradient show an enhancement in fill factor and open circuit voltage (V oc) by 5% and 20 mV respectively, with respect to a cell without the graded band gap active layer. Such an enhanced device performance is attributed to reduction in recombination loss of photo-generated electron hole pairs. The effect of this photo-current loss was investigated in the electrical bias dependent external quantum efficiencies (EQE), illumination dependent current-voltage measurements and dark current-voltage characteristics. The device parameters like reverse saturation current density (J o), series resistance (R s) and diode quality factor (n) were also estimated. In comparison to the cell without the composition gradient, the EQE shows a reduced recombination loss across the whole wavelength range for the cell with the CG. Furthermore, the introduction of the CG results in a significantly increased shunt resistance from 720 to 1200 Ω.cm 2. The estimated n values of the cells under dark operating condition, decreases from 1.8 to 1.7 along with J o from 3 × 10 −7 down to 4.5 × 10 −8 A/cm 2 with CG, while the same parameters decreased from 3.73 to 3.06, 2.96 × 10 −6 to 3.05 × 10 −7 A/cm 2 respectively under AM1.5G insolation.

Made available in DSpace on 2018-12-11T16:46:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-04-15 The present study shows how electronic parameters (e.g. band gap energy, band edge positions) on semiconductors affect photoelectrochemical activity in simulated solar light using WO3, TiO2 and WO3/TiO2 as model systems. Hydrothermal synthesis was conducted to study heterostructure (HE) formation, which the loading of WO3 in TiO2 structure were varied to 20, 40 and 80 wt%. Scanning electron microscopy images show that WO3 and TiO2 particles are in contact with each other and the synthesis method as well as the deposition method are appropriate for the formation of WO3/TiO2 HE film. Important findings were obtained with a hole scavenger during photoelectrochemical characterization of WO3/TiO2–40 wt% film. This strategy was effective to clearly distinguish charge transport from charge separation, the essential mechanisms that affect water splitting which are often misinterpreted experimentally for HE. The hole scavenger experiment depicts the increase by 17.5% in photocurrent density for the WO3/TiO2–40 wt% film as compared to WO3 film, corresponding to 210 and 12 μA cm−2 vs Ag/AgCl respectively. Additionally, this HE film showed water oxidation initiated at lower applied potentials and indicating that coupling of the materials resulted in optimization of band edge properties for water splitting with the increase on light absorption at the visible range. Flat band potential was determined by the Mott-Schottky plot and it indicated the difference of 1.08 V vs Ag/AgCl between TiO2 and WO3 potentials, which makes the charge injection from one structure to another effective and thermodynamically stable for charge separation. A charge carrier density of 1.59 × 1020 was observed for the WO3/TiO2–40 wt% and it supports the best photoelectrochemical performance for water oxidation. Chemistry Department Federal University of São Carlos Chemistry Department Sao Paulo State University UNESP Materials Science and Engineering Department Federal University of São Carlos Embrapa Instrumentation Chemistry Department Sao Paulo State University UNESP

We measured transient absorption in α-Al2O3 after pulsed electron beam irradiation to analyze the relaxation process of excited states. We used two measurement systems to obtain transient absorption in nanosecond and picosecond time scales. In the nanosecond time scale, we observed a band at 610 nm in addition to a shoulder at 420 nm. This observation is consistent with that in a previous paper, and these bands are attributed to Al interstitials according to the paper. The decay behavior of these bands was significantly different in the picosecond time scale. The difference in the decay kinetics strongly suggests that the band at 610 nm and the shoulder at 420 nm are attributed to two kinds of Al interstitials.

Green tunnel-junction (TJ) light-emitting diodes (LEDs) are investigated theoretically in this letter. The influence of Auger recombination on the optical performance of green single LED and TJ LED is explored. Simulation results show that non-uniform carrier distribution and Auger recombination are critical issues influencing the performance of conventional green LED. The TJ LED can be operated at relatively low current density that possesses suppressed Auger recombination and high quantum efficiency when compared with its single LED counterpart at the same level of output power. Simulated wall-plug efficiency of the TJ LEDs with two and three unit LEDs is increased from 5.67% to 10.51% and 12.54%, respectively, in comparison with the single LED when the output power is 21 mW.

In this paper, the improvement of the method measuring the junction temperature of light-emitting diodes (LEDs) has been studied experimentally. A practical method is proposed with only three measurement procedures. With the consideration of indium (In) composition and blue shift, the method has a high applicability, which is practical for the LED chips vary from blue to green chips under different currents, including the packaged chips. On the other hand, according to the experimental and derived results, the junction-temperature difference and peak-wavelength shift in both blue-shift and red-shift fields show similar parabolic-like relations. To simplify the experimental processes, dual-wavelength LEDs were fabricated and measured instead of conventional single-wavelength LEDs.

The pure ZnO, pure MgO NPs and ZnO/MgO (1:1) nanocomposite were synthesized by solution combustion method by using Oxalyl dihydrazide (ODH) as fuel. The synthesized samples were characterized by XRD, FTIR, UV-DRS, SEM and EIS. The SEM analysis revealed that the presence of porous and foamy cave like structures in ZnO/MgO (1:1) nanocomposite suitable for efficient photocatalysis. The Optical studies showed that increased band gap from 3.328 to 3.598 eV for pure ZnO and ZnO/MgO (1:1) nanocomposite respectively. The photocatalytic studies towards decolorization of IC dye under UV light by using ZnO/MgO (1:1) nanocomposite showed 78% of decolorization efficiency for irradiation time of about 90 minutes. The reason for enhancement attributed to increase in the separation of the photo induced electron hole pairs. Therefore ZnO/MgO (1:1) nanocomposite can be exercised as prospective photocatalyst.

In efficient solar energy conversion for environmental and energy applications, the use of visible-light-active photocatalysis as a green and sustainable technology has become a promising technology. A visible-light-active photocatalyst (λ > 400 nm) for efficiently harvesting solar energy and addressing a recent primary concern has been designed and fabricated. An effective separation of photo-generated electron hole pairs and their rapid transport to the semiconductor surface is required for high-efficiency solar photocatalysis; therefore, significant efforts have been devoted to designing and developing hetero-binuclear oxo-bridged systems, owing to their unique physical and electronic properties, which make them promising candidates for photocatalysis. These materials exhibit excellent light-harvesting properties, due to metal-to-metal charge-transfer (MMCT) excitation, and possess band-gap energies that are more suitable for solar light absorption. Recently, hetero-binuclear oxo-bridged systems have facilitated the rapid progress in enhancing photocatalytic efficiency under visible light irradiation; therefore, this mini-review aims to provide a systematic study of heteronuclear oxo-bridged systems for environmental decontamination and artificial photosynthesis (water splitting and photocatalytic CO2 reduction). This review provides a few perspectives on the challenges hindering the further advancement of oxo-bridged materials for application in photocatalysis.

Photogeneration of excess charge carriers in semiconductors produces electronic strain. Under transient conditions, electron-hole pairs may be separated across a potential barrier. Using time-resolved X-ray diffraction measurements across an intrinsic AlGaAs/n-doped GaAs interface, we find that the electronic strain is only produced by holes, and that electrons are not directly observable by strain measurements. The presence of photoinduced charge carriers in the n-doped GaAs is indirectly confirmed by delayed heat generation via recombination.

The band gap controlled photocatalyst (Zn0.74Cu0.13In2S3.805) was prepared via a simple one-step solvothermal method. The effects of doping of Cu+ and excess In on the photocatalytic activity of ZnIn2S4 photocatalyst were investigated. In addition, optical properties, surface morphology and crystal structure were evaluated. The maximum H2 evolution rate (2370 &micro, mol h&minus, 1 g&minus, 1) was achieved with Zn0.74Cu0.13In2S3.805, which was about five times higher than that of untreated ZnIn2S4 under visible light (&lambda, &ge, 420 nm). The band gap of Zn0.74Cu0.13In2S3.805 decreased to 1.98 eV by raising the maximum position of the valence band, compared to ZnIn2S4. Furthermore, the recombination of electron hole pairs was effectively reduced. This research contributes to the development of highly active photocatalysts under visible light.

All-solid Z-scheme Bi–BiOCl/AgCl heterojunction microspheres are successfully prepared via hydrothermal, NaBH4 reduction and chemical deposition strategy. They are tested by various characterization methods, and they show that metal Bi is present after reduction and AgCl nanoparticles are successfully compounded onto BiOCl. Bi plays the role of a bridge connecting the two semiconductors of BiOCl and AgCl. All-solid Z-scheme heterojunction structures are formed successfully. The narrow band gap of the Z-scheme Bi–BiOCl/AgCl heterojunction microspheres is about 2.17 eV, which can expand the optical response range. Moreover, the photocatalytic hydrogen production rate still reaches 198.2 μmol h–1 g–1, extends the electron transport life, inhibits the recombination of electron hole pairs, and improves the photocatalytic activity.