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Synthesizing nanopores which mimic the functionality of ion-selective biological channels has been a challenging yet promising approach to advance technologies for precise ion-ion separations. Inspired by the facilitated fluoride (F-) permeation in the biological fluoride channel, we designed a highly fluoride-selective TiO2 film using the atomic layer deposition (ALD) technique. The subnanometer voids within the fabricated TiO2 film (4 A < d < 12 A, with two distinct peaks at 5.5 and 6.5 A), created by the hindered diffusion of ALD precursors (d = 7 A), resulted in more than eight times faster permeation of sodium fluoride compared to other sodium halides. We show that the specific Ti-F interactions compensate for the energy penalty of F- dehydration during the partitioning of F- ions into the pore and allow for an intrapore accumulation of F- ions. Concomitantly, the accumulation of F- ions on the pore walls also enhances the transport of sodium (Na+) cations due to electrostatic interactions. Molecular dynamics simulations probing the ion concentration and mobility within the TiO2 pore further support our proposed mechanisms for the selective F- transport and enhanced Na+ permeation in the TiO2 film. Overall, our work provides insights toward the design of ion-selective nanopores using the ALD technique.

Summary Hydrogen peroxide (H2O2) is receiving growing interest for energy storage because it can be locally synthesized from renewable energy through the two-electron water oxidation and the two-electron oxygen reduction reactions. Recently, engineering the microenvironment of existing catalysts has become a promising approach to address the activity, selectivity, and stability challenges of H2O2 synthesis and fuel cells, reducing the gap between theoretical prediction and experimental observations. We summarize these progresses from a multi-scale perspective, including tailoring the active sites on the catalytic surface, engineering the interface near the reactive sites, and improving the device design to achieve selective H2O2 conversion. Such strategies tune the thermodynamic energy barriers and reaction pathways, facilitate mass transfer for reactants and products, and stabilize the products and catalytic surfaces. The discussions here are expected to stimulate further efforts to achieve efficient on-site H2O2 production and power generation by H2O2 with high round-trip efficiency.

Highly robust, swiftly reversible thermochromic nature of a two-dimensional (2D) perovskite of (PDMA)(CH3NH3)n-1PbnI3n+1, nominally prepared as n = 2 is found, where PDMA = C6H4(CH2NH3)2. A wide band gap variation from 700 to 430 nm is observed between room temperature and >60 °C under ambient conditions, resulting from moisture absorption and desorption. X-ray diffraction and Fourier-transform infrared spectroscopy are performed to analyze the hydrated and dehydrated states. Furthermore, the (PDMA)(CH3NH3)n-1PbnI3n+1 film is demonstrated as an active material for smart windows and thermochromic solar cells, which could lower the inside air temperature in an enclosed space and supply a power conversion efficiency of more than 0.5% at a high ambient temperature, respectively. Overall, we may pave a pathway for exploring the novel phenomena and applications of Dion-Jacobson 2D perovskites.

Using substrates at room temperature or at 110 °C, two-dimensional (2D) perovskite films and solar cells using mixed butylammonium (BA) and formamidinium (FA) cations, i.e., (BA)2(FA)n−1PbnI3n+1 (n...

One key objective in electrocatalysis is to design selective catalysts, particularly in cases where the desired products require thermodynamically unfavorable pathways. Electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron water oxidation reaction (2e− WOR) requires a +0.54 V higher potential than four-electron O2 evolution. So far, best-performing electrocatalysts require considerable overpotentials before reaching peak faradaic efficiency. We present Mn-alloyed TiO2 coatings prepared by atomic layer deposition (ALD) and annealing as a stable and selective electrocatalyst for 2e− WOR. Faradaic efficiency of >90% at < 150 mV overpotentials was achieved for H2O2 production, accumulating 2.97 mM H2O2 after 8 hours. Nanoscale mixing of Mn2O3 and TiO2 resulted in a partially filled, highly conductive Mn3+ intermediate band (IB) within the TiO2 mid-gap to transport charge across the (Ti,Mn)Ox coating. This IB energetically matched that of H2O2-producing surface intermediates, turning a wide bandgap oxide into a selective electrocatalyst capable of operating in the dark. However, the high selectivity is limited to the low overpotential regime, which limits the system to low current densities and requires further research into increasing turn-over frequency per active site.

Arrays of GaAs nanowires have been grown by selective-area metal–organic chemical-vapor deposition (MOCVD) onto photoactive planar Si substrates. This tandem, vertical-wire-array-on-planar absorber...

Surface plasmons (SPs) of metals enable the tight focusing and strong absorption of light to realize an efficient utilization of photons at nanoscale. In particular, the SP-generated hot carriers have emerged as a promising way to efficiently drive photochemical and photoelectric processes under moderate conditions. In situ measuring of the transport process and spatial distribution of hot carriers in real space is crucial to efficiently capture the hot carriers. Here, we use electrochemical tip-enhanced Raman spectroscopy (EC-TERS) to in situ monitor an SP-driven decarboxylation and resolve the spatial distribution of hot carriers with a nanometer spatial resolution. The transport distance of about 20 nm for the reactive hot carriers is obtained from the TERS imaging result. The hot carriers with a higher energy have a shorter transport distance. These conclusions can be guides for the design and arrangement of reactants and devices to efficiently make use of plasmonic hot carriers., Revealing the spatial distribution of hot carriers in real space is crucial to their efficient utilization. Here, the authors show that in-situ electrochemical tip-enhanced Raman spectroscopy is able to resolve the spatial distribution of reactive hot carriers with a nanometer spatial resolution.

A TiO2 coating was grown on a CdTe absorber by atomic layer deposition for stabilization against its photocorrosion during photoelectrochemical water splitting. Under simulated sunlight (AM 1.5G, 1...

Y3Al5-xGaxO12:Ce3+,V3+ (YAG:Ce) has excellent chemical stability and unprecedented luminous efficiency. Its strong photoresponsive property is thoroughly utilized in designing excellent optical information storage device. Here, the remarkable photoconductivity of YAG:Ce is exploited to demonstrate a hybrid YAG:Ce-silicon device that shows high speed terahertz wave spatial modulation. A wide terahertz spectra modulation is observed under different pump powers in frequency range from 0.2 to 1.8 THz. Furthermore, a dynamic control of the terahertz wave intensity is also observed in the transmission system. The modulation speed and depth of the device is measured to be 4 MHz (vs 0.2 kHz)and 83.8%(vs50%) for bare silicon, respectively. The terahertz transmission spectra exhibits highly efficiency terahertz modulation by optically pumping a YAG:Ce film on silicon with low optical pump fluence.

Understanding the interactions between molecules and metal surfaces is of widespread importance in electrochemistry, sensing, medical imaging/targeting, molecular electronics and spintronics. Although many techniques have characterized the molecule-metal transient bonds, conflicting conclusions arise from their buried location and heterogeneity, while single-molecule probes are scarce. Confinement of optical fields to picometre length-scales around adatoms (termed picocavities [1] , Fig. 1a ) has enabled tip-enhanced and surface-enhanced Raman spectroscopies (TERS and SERS, Fig. 1e ) of single-molecules. However how adatoms change with molecule-metal interactions, with light (both key ingredients in photocatalysis), and how they link to picocavity formation in metal nanogaps is not understood.

Electrochemical synthesis of hydrogen peroxide from oxygen and water can be a cost-effective and energy-efficient alternative to the traditional approach which requires high energy input and expens...

The electrical transport in amorphous titanium dioxide (a-TiO2) thin films deposited by atomic-layer deposition (ALD), and across heterojunctions of p+-Si|a-TiO2|metal substrates that had various top metal contacts, has been characterized by AC conductivity, temperature-dependent DC conductivity, space-charge-limited current (SCLC) spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and current density versus voltage (J-V) characteristics. Amorphous TiO2 films were fabricated using either tetrakis(dimethylamido)-titanium (TDMAT) with a substrate temperature of 150 °C or TiCl4 with a substrate temperature of 50, 100, or 150 °C. EPR spectroscopy of the films showed that the Ti3+ concentration varied with the deposition conditions, and increases in the concentration of Ti3+ in the films correlated with increases in film conductivity. Valence-band spectra for the a-TiO2 films exhibited a defect-state peak below the conduction-band minimum (CBM), and increases in the intensity of this peak correlated with increases in the Ti3+ concentration measured by EPR as well as with increases in film conductivity. The temperature dependent conduction data showed Arrhenius behavior at room temperature with an activation energy that decreased with decreasing temperature, suggesting that conduction did not occur primarily through either the valence or conduction bands. The data from all of the measurements are consistent with a Ti3+ defect-mediated transport mode involving a hopping mechanism with a defect density of 1019 cm-3, a 0.83 wide defect-band centered 1.47 eV below the CBM, and a free-electron concentration of 1016 cm-3. The data are consistent with substantial room-temperature anodic conductivity resulting from introduction of defect states during the ALD fabrication process as opposed charge transport intrinsically associated with the conduction band of TiO2.

A tunable blue random laser based on solid waveguide gain films with silver nanoparticles (NPs) and SiO2 NPs is demonstrated. Localized surface plasmon resonance (LSPR) property and multiple scattering are proven playing an important role simultaneously. The tunability of the blue random laser is realized by simply roughing and changing the thickness of the solid waveguide gain films. To our knowledge, it is the first time using this method to achieve a wide wavelength tuning range of ∼24 nm.

In the field of surface plasmon-mediated photocatalysis, the coupling reactions of p-aminothiophenol (PATP) and p-nitrothiophenol (PNTP) to produce p, p'-dimercaptoazobenzene (DMAB) are the most widely investigated systems. However, a clear understanding of the structure-function relationship is still required. Here, we used tip-enhanced Raman spectroscopy (TERS) to study the coupling reactions of PATP and PNTP on well-defined Ag(111) and Au(111) surfaces using 632.8 and 532 nm lasers. On Au(111), the oxidative coupling of PATP can proceed under irradiation by a 632.8 nm laser, and the reductive coupling of PNTP can only occur under irradiation by a 532 nm laser. Neither wavelength of laser light can induce the coupling reactions of these two molecules on Ag(111). Density functional theory (DFT) was used to calculate the stable adsorption configurations of PATP and PNTP on Ag(111) and Au(111). Both the adsorption configurations of the two molecules on the surfaces and laser energies were, experimentally and theoretically, found to determine whether the coupling reactions can occur on different substrates. These results may help the rational design of photocatalysts with enhanced reactivity.

Absorption and photoluminescence spectra at various temperatures below 200 K had been used to study the optical properties of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) fi...

Films of two-dimensional (2D) perovskite (PEA)2(MA)n-1PbnI3n+1 (PEA = phenylethylammonium, MA = methylammonium) series (n = 1, 2, 3) show high stability in contrast to their three-dimensional counterparts. Development of an effective means to fabricate 2D perovskite solar cells which can achieve a better power conversion efficiency (PCE) and have less current density-voltage (J-V) hysteresis, is crucial to boost their applications. We present a one-step solution process to fabricate the 2D perovskite (PEA)2(MA)2Pb3I10 as light absorbers in solar cells by adding methylammonium acetate (MAAc) in a precursor solution. With an appropriate molar ratio of MAAc, the 2D perovskite films show a smoother surface, higher coverage, and better crystallinity, resulting in an optimal PCE of 5.7%, and importantly, no J-V hysteresis.

Photocatalytic water splitting using particulate suspensions is a promising approach for achieving large-scale production of renewable hydrogen fuels. Previous studies have hypothesized that band energy levels of such photocatalysts in water are both flat and symmetrical, and charge separation in such photocatalysts is driven by random charge carrier diffusion. However, it is not well understood how the observed asymmetry of carrier diffusion is achieved during photocatalysis. To fully understand this charge separation process, we used double-side polished, intrinsic silicon as a model light absorber and manipulated the direction of charge-carrier diffusion using combinations of carrier-selective contacts. Degenerately p-type doped and n-type doped silicon, along with the as-grown and annealed TiO2 overlayers grown by atomic layer deposition, was used as carrier selective back and front contacts, respectively. The protective TiO2 layers along with nickel oxide co-catalysts enabled bi-functional, stable silicon photoelectrodes for photoelectrochemical hydrogen evolution and water oxidation in alkaline solution. A device simulation was applied to analyse the experimental results and further gain understanding on the charge separation process in photocatalysts involving semiconductor/liquid junctions. Combined experimental and simulation studies indicated that the contacts established asymmetric band bending inside the intrinsic silicon layer and drove directional charge separation, primarily carrier diffusion. By scaling down the thickness of the silicon layer in the simulation, analogies of charge separation in particulate photocatalysts can be drawn. Based on the findings from intrinsic silicon, we further revealed that photocatalysts generally do require asymmetric band bending to drive diffusional charge separation and that a small band edge offset of 0.45 eV between reductive and oxidative catalytic sites can provide a sufficient, steady-state photovoltage of over 1.23 V for overall water splitting by using a model SrTiO3 absorber. This study provides insightful guidance for designing efficient and stable particulate photocatalysts especially those using Si and III–V semiconductors with protective layers such as TiO2.

Developing efficient earth-abundant transition metal-based electrocatalysts for the hydrogen evolution reaction (HER) is crucial for hydrogen production at scale. This paper reports that the buried electrocatalytic interfaces between Ni–Fe sulfide (NiFeS) nanosheets and TiO2 conformal coatings (about 5 nm) achieved remarkable HER activity improvement, lowering the HER overpotential from −170 mV to −107 mV at −50 mA cm−2 in a base. Non-HER active, permeable TiO2 coatings grown by atomic layer deposition (ALD) achieved continuous fine-tuning of the electronic properties at the buried TiO2/NiFeS interfaces, as a novel strategy and the main factor for electron accumulation at the interface. Core-level and valence band X-ray photoelectron spectroscopy (XPS) was used to investigate the TiO2 electronic-structure tuning effect on the charge-transfer energetics during the HER. Their alkaline HER mechanism was elucidated by supplementing characterizations of membrane permeation, Tafel slope, and synchrotron X-ray absorption spectroscopy, which verified that the buried TiO2/NiFeS interfaces are electrocatalytically active. This study offers a general strategy for improving the charge-transfer kinetics of an electrocatalytic system by confining catalysis at a permeable solid–solid interface. The broad applicability of permeable and tunable coatings potentially accelerates the optimization of earth-abundant catalysts to achieve high performance under operationally relevant conditions.

Three types of membrane-less photoelectrochemical (PEC) devices for solar-driven hydrogen peroxide (H2O2) production have been proposed, including (a) a H2O2 electrolyzer; (b) a photoelectrode-based PEC device; and (c) particulate photocatalysts in a suspension reactor. These devices can produce H2O2 from sunlight, water, and oxygen in air as the only inputs. Their respective efficiency limits were calculated by using the measured performance of H2O2 evolving electrocatalysts and by assuming idealized 100% selectivity for H2O2 accumulation, and by using the energy-conversion performance of light absorbers at their Shockley–Queisser limit. Multi-physics models for the three device configurations were employed for evaluating their electrochemical polarization behaviour as a function of the operating current density and for quantifying the respective contribution from the catalyst overpotential loss, the resistive loss between the cathode and anode, and the Nernstian potential loss due to pH gradients across the electrolyte. For particulate photocatalysts in a suspension, the concept of a non-zero light intensity threshold was for the first time applied to account for net positive H2O2 accumulation, which implies that the most efficient photocatalyst suspension should not fully absorb sunlight. The maximum solar-to-H2O2 conversion efficiency for a photoelectrode-based device was found to be 20.0%, fundamentally limited by the photocurrent density that is matched by dual absorbers in tandem series under 1-sun illumination. The maximum solar-to-H2O2 conversion efficiency for a particulate photocatalyst suspension can achieve 24.5–27.5% with a single-absorber band gap of 1.5–1.7 eV, depending on particle sizes. The modelling outcomes emphasize the importance of water-oxidation selectivity for achieving H2O2 accumulation towards molar concentration levels, and should guide the PEC H2O2 device implementation as the activity and selectivity of H2O2-evolving electro-catalysts continue to improve.

We here present an innovative approach to increase the electron density of metallic Pd nanoparticles loaded on TiO2 photocatalysts by coordinating Pd with surface-anchored organic ligands. X-ray ph...

The temperature dependence of absorption and photoluminescence (PL) spectroscopies were used to study the optical properties of 2D perovskite films, including n = 1 and 3 of (PEA)2(CH3NH3)n−1[PbnI3n+1] (PEA = C6H5(CH2)2NH3). In (PEA)2[Pb1I4] (PEPI), excitons coupling to optical phonons with an average energy of ∼30 meV dominate the photophysics of absorption and PL. (PEA)2(CH3NH3)2[Pb3I10] (shortened as PMPI3), nominally prepared as n = 3, actually was a mixture of multiple layered perovskites with various n. In absorption, a PMPI3 film presents respective n materials’ excitonic features, coupling to phonons with an average energy of ∼30 meV; in analyzing PL peaked singly at ∼1.6 eV and its width as a function of temperature, we found that PMPI3 behaves like PEPI at around 80 K but like 3D perovskite near room temperature, with three times larger electron–phonon interaction strength compared to that in PEPI.

Enhancing the chemical and physical properties of the polyamide active layer of thin-film composite (TFC) membranes by surface coating is a goal long-pursued. Atomic layer deposition (ALD) has been proposed as an innovative approach to deposit chemically robust metal oxides onto membrane surfaces due to its unique capability to control coating conformality and thickness with atomic scale precision. This study examined the potential to coat the surface of TFC reverse osmosis (RO) and nanofiltration (NF) membranes via ALD of TiO2. Our results suggest that the optimal ALD conditions, the film growth kinetics, and the depth of deposition are different for RO and NF membranes due to the different diffusive transport of ALD precursors through the membrane pores. The TiO2 coating mainly located at the surface of the RO membrane; in contrast, the TiO2 coating extended to the depth of the NF membrane. The TiO2 coating degraded membrane water permeability and salt rejection beyond 10 cycles of ALD, the condition commonly employed in previous ALD-based membrane modification studies. Instead, this study showed that with fewer than 10 cycles, the TiO2 coating of RO membrane increased the membrane surface charge without negatively impacting water permeability and salt rejection. For the NF membranes, the coating of TiO2 inside their pores led to the tuning of pore sizes and increased the rejection of selected solutes.

Quasi-two-dimensional (2D) perovskites recently came into the focus because of their moisture stability. In addition to ambient air, light illumination could also cause degradation for the film of 2D perovskites, however, few studies have investigated their photostability. Here, we work on light-induced photoluminescence quenching, as well as the degradation of quasi-2D perovskites of PEA2MAn−1PbnI3n+1 (n = 3 nominally, PEA+ = C6H5(CH2)2NH3+, MA+ = CH3NH3+). Light-induced photoluminescence (PL) quenching generally happens with different speeds, depending on the wavelength and intensity of the laser as well as the film’s environment. With red light (635 nm) illumination, the film does not decompose into ambient air with an intensity below ~500 mW/cm2, although in general, a higher laser intensity and/or higher photon energy (447 nm) could render the decomposition process easier and faster. On the other hand, when the film is in a vacuum, both light-induced PL quenching and film degradation are significantly suppressed. Furthermore, we find that the multiphase of n = 1, 2, 3 in the PEA2MA2Pb3I10 film decomposes together and that the degradation processes begin with the collapses of the crystalline structures.

Semiconductors of narrow bandgaps and high quantum efficiency have not been broadly utilized for photocatalytic coevolution of H(2) and O(2) via water splitting. One prominent issue is to develop effective protection strategies, which not only mitigate photocorrosion in an aqueous environment but also facilitate charge separation. Achieving local charge separation is especially challenging when these reductive and oxidative sites are placed only nanometers apart compared to two macroscopically separated electrodes in a photoelectrochemical cell. Additionally, the driving force of charge separation, namely the energetic difference in the barrier heights across the two type of sites, is small. Herein, we used conformal coatings attached by nanoscale cocatalysts to transform two classes of tunable bandgap semiconductors, i.e., CdS and GaInP(2), into stable and efficient photocatalysts. We used hydrogen evolution and redox-mediator oxidation for model study, and further constructed a two-compartment solar fuel generator that separated stoichiometric H(2) and O(2) products. Distinct from the single charge-transfer direction reported for conventional protective coatings, the coating herein allows for concurrent injection of photoexcited electrons and holes through the coating. The energetic difference between reductive and oxidative catalytic sites was regulated by selectivity and local kinetics. Accordingly, the charge separation behavior was validated using numerical simulations. Following this design principle, the CdS/TiO(2)/Rh@CrO(x) photocatalysts evolved H(2) while oxidizing reversible polysulfide redox mediators at a maximum rate of 90.6 μmol⋅h(−1)⋅cm(−2) by stacking three panels. Powered by a solar cell, the redox-mediated solar water-splitting reactor regenerated the polysulfide repeatedly and achieved solar-to-hydrogen efficiency of 1.7%.

Semiconductors of narrow bandgaps and high quantum efficiency have not been successfully utilised for coevolving photocatalysis despite the widely demonstrated protective coating schemes. Herein, we showcase a general strategy of using conformal coatings and cocatalysts energetic properties to transform CdS powders and GaInP2 films into stable and efficient photocatalysts for coevolution of H2 and reversible redox couples. A scalable redox-mediated solar water-splitting reactor was constructed, regenerating the redox mediators while evolving O2 in a separate compartment. Distinct from the single direction of charge transfer found with conventional photoelectrode stabilisation, the coating herein allows both photo-excited electrons and holes to spatially separate and inject simultaneously to the respective reductive and oxidative sites. With TiO2 stabilisation, CdS particles produced H2 continuously for 150 hours. Under simulated sunlight, solar-to-hydrogen (STH) efficiency of 5.9% and 9.4% can be achieved for the CdS and GaInP2 panels, respectively, by stacking multiple panels and matching the rate of redox regeneration to that of H2 production.

Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive technique with molecular specificity, making it an ideal analytical tool in various fields. However, the breadth of practical applications of SERS has been severely limited because it is still a great challenge to achieve simultaneously a high sensitivity and a high reproducibility. Herein, we report a highly controllable method to fabricate periodic bowtie SERS substrates with a narrow nanogap, high SERS enhancement, and good uniformity over a large area. The periodic bowtie template is first fabricated over a gold film by holographic lithography (HL), followed by Au deposition to obtain a conductive plasmonic bowtie array. The gap size is then narrowed down by pulsed electrodeposition of Ag simultaneously monitored in situ by electrochemical dark field spectroscopy. Thus, we are able to observe the most sensitive change in the scattering spectra when the gap is just about to merge and obtain uniform SERS substrates with a gap size down to around 5 nm. The average enhancement factor of 5 × 107 to 1 × 108 is obtained, which is 50 times larger than that from Au nanoparticle-assembled substrates and 140 times larger than that from commercial Klarite chips. This substrate offers a promising opportunity for SERS practical applications.

The multiple light scattering of nanoporous (NP) GaN was systematically studied and applied to the color down-conversion for micro-light-emitting diode (LED) display applications. The transport mean free path (TMFP) in NP GaN is 660 nm at 450 nm (light wavelength), and it decreases with a decreasing wavelength. It was observed that the short TMFP of the NP GaN increased the light extinction coefficient at 370 nm by 11 times. Colloidal QDs were loaded into a half 4″ wafer scale NP GaN, and 96 and 100% of light conversion efficiencies for green and red were achieved, respectively. By loading green and red QDs selectively into NP GaN mesas, we demonstrated the RGB microarrays based on the blue-violet pumping light with green and red color converting regions.

Underpotential deposition offers a predominant way to tailor the electronic structure of the catalytic surface at the atomic level, which is key to engineering materials with a high activity for (electro)catalysis. However, it remains challenging to precisely control and directly probe the underpotential deposition of a (sub)monolayer of atoms on nanoparticle surfaces. In this work, we in situ observe silver electrodeposited on gold nanocrystals surface from sub-monolayer to one monolayer by designing a highly sensitive electrochemical dark field scattering setup. The spectral variation is used to reconstruct the optical “cyclic voltammogram” of every single nanocrystal for understanding the underpotential deposition process on nanocrystals, which cannot be achieved by any other methods but are essential for creating novel nanomaterials., Underpotential deposition (UPD) is important to modify the surface properties of nanocrystals. Here, the authors show the application of in situ electrochemical dark field spectroscopy in identifying the UPD processes of silver on different facets of gold nanocrystals at the single nanoparticle level.

This paper reports the simultaneous output of 358.7nm and 420.3nm laser generated by two-photon excitation (52 S1/2→62 D5/2, TPE) and four-wave mixing effect (FWM) in rubidium system for the first time. Unlike some fluorescent signals, this four-wave mixing beam has a high monochromaticity and extreme directivity and can be used as a laser source. In this study, we also measured the fluorescence lines in the range of 300-820 nm under 52 S1/2→62 D5/2 TPE, and studied other transitions that may occur. The experimental results show that the blue-violet laser produced by this alkali metal rubidium four-wave mixing can provide a new laser source for underwater laser communication, display technology, fluorescence excitation, Raman spectroscopy, marine resource detection, laser biomedicine, lithography, high density information storage and other fields.

Random lasing from a polydimethylsiloxane substrate prepared from abalone shell by soft lithography was investigated. The substrate has better scattering efficiency than abalone shell and its groove structure can support both incoherent and coherent random lasing when covered with a layer of dye solution. When employing rhodamine 640 dye as gain medium, a dual-band random laser signal based on the mechanism of optical feedback intensity and mode competition can be observed, where the signals of the two bands are shown as incoherent and coherent random lasing regimes respectively. Speckle-free imaging is achieved by using incoherent and coherent random lasers as illumination sources and imaging effects are compared. This research shall promote the development of random lasers in the fields of illumination and imaging.

Discovering electrode materials with exceptional capacitance, an indicator of the ability of a material to hold charge, is critical for developing capacitive deionization devices for water desalina...

We present the time-resolved character of stimulated Brillouin scattering (SBS) and backward stimulated Raman scattering (BSRS) in heavy water and its application in Coherent Anti-Stokes Raman Scattering (CARS) technique. A nanosecond laser from a frequency-doubled Nd: YAG laser is introduced into a heavy water cell, to generate SBS and BSRS beams. The SBS and BSRS beams are collinear, and their time resolved characters are studied by a streak camera, experiment show that they are ideal source for an alignment-free CARS system, and the time resolved property of SBS and BSRS beams could affect the CARS efficiency significantly. By inserting a Dye cuvette to the collinear beams, the time-overlapping of SBS and BSRS could be improved, and finally the CARS efficiency is increased, even though the SBS energy is decreased. Possible methods to improve the efficiency of this CARS system are discussed too.

Accomplishing acid-stable water oxidation is a critical matter for achieving both long-lasting water-splitting devices and other fuel-forming electro- and photocatalytic processes. Because water ox...

Plasmon-induced magnetic resonance has shown great potentials in optical metamaterials, chemical (bio)-sensing, and surface-enhanced spectroscopies. Here, we have theoretically and experimentally revealed (1) a correspondence of the strongest near-field response to the far-field scattering valley and (2) a significant improvement in Raman signals of probing molecules by the plasmon-induced magnetic resonance. These revelations are accomplished by designing a simple and practical metallic nanoparticle-film plasmonic system that generates magnetic resonances at visible-near-infrared frequencies. Our work may provide new insights for understanding the enhancement mechanism of various plasmon-enhanced spectroscopies and also helps further explore light-matter interactions at the nanoscale.

The development of low overpotential, non-precious metal oxide electrocatalysts is important for sustainable water oxidation using renewable energy. Here we report the fabrication of nano-interfaces between MnOx nanoscale islands and NiFe layered double hydroxide (LDH) nanosheets, which were chosen as baseline electrocatalysts for OER activity tuning. The MnOx nano-islands were grown on the surfaces of NiFe-LDH nanosheets by atomic layer deposition (ALD). Morphological and structural characterization indicated that the MnOx formed flat nanoscale islands which uniformly covered the surfaces of NiFe-LDH nanosheets, giving rise to a large density of three-dimensional nano-interfaces at the NiFe-LDH/MnOx/electrolyte multi-phase boundaries. We showed by X-ray spectroscopic characterization that these nano-interfaces induced electronic interactions between NiFe-LDH nanosheets and MnOx nano-islands. Through such modifications, the Fermi level of the original NiFe-LDH was lowered by donating electrons to the MnOx nano-islands, dramatically boosting the OER performance of these electron-deficient NiFe-LDH catalysts. Using only 10 cycles of ALD MnOx, the MnOx/NiFe-LDH nanocomposites exhibited remarkable and enhanced electrocatalytic activity with an overpotential of 174 mV at 10 mA cm−2. This work demonstrates a promising pathway for tuning transition metal electrocatalysts via a generic ALD surface modification technique.

Partial circularly polarized photoluminescence (CPL) with a polarization degree (P) of 2% from CH3NH3PbBr3 film at 77 K is observed, excited by a circularly polarized 532 nm laser. However, P decreases to 0.3% when excited using a circularly polarized 447 nm laser, and to zero using a linear polarized laser. The Hanle effect is measured to study spin relaxation in CH3NH3PbBr3 film, yielding a spin lifetime of ∼240 ps at 77 K, which however becomes one order of magnitude smaller when the temperature increases to 110 K. The existence of a CPL that is dependent on the helicity of the excitation laser, and the unexpectedly long spin lifetime with large spin–orbit coupling, suggest the potential of hybrid perovskites for spintronic applications.

Mixed halide perovskites are considered to have great application prospects in the field of optoelectronics due to their bandgap tunability. However, their applications are limited by phase instability under illumination. Here, we have used PL measurement to investigate phase segregation in mixed halide perovskite films with and without post-treatment using methylammonium halide solutions. Our findings reveal the PL evolution is strongly dependent on the morphology of perovskite films: the PL peak from small I-rich clusters is observed at the initial time in the films with unreacted lead halides, accompanied by faster PL evolution with increase of the concentration of methylammonium halide solution; adding excess methylammonium halide solution to the perovskite film leads to the disappearance of that PL peak. We attribute the difference of PL evolution in various films to the different evolution of local electric fields, which are induced by carrier trapping at grain boundaries. Our results indicate the local electric fields play an essential role in the halide segregation process.

Collimated ultraviolet (UV) light is generated via four-wave mixing (FWM) in cesium vapor by continuously tuning the wavelength of the pump laser. Terahertz (THz) Stokes light is generated by the stimulated Raman scattering (SRS) effect in the FWM process, and its frequency is adjustable. When exciting the cesium atom to a virtual level using different combinations of pump lasers (P1 and P2), the strength distribution of UV light is asymmetric, which can be explained through a phase-matching mechanism. Furthermore, the SRS effect and phase matching influence the FWM.

Here we reported on a tunable and stable random laser based on the abalone shell. The groove structure on the inner surface of abalone shell can support coherent random lasing when covered with a layer of dye doped film. By changing the pump position, the emission spectrum wavelength can be tuned by 12.10 nm due to the random distribution of the groove structure on the inner surface of abalone shell. The random laser can also be tuned by 13.85 nm using different concentrations of dye solutions. Furthermore, several different kinds of dyes were used to extent the emission wavelength range of the random laser. The normalized scattering efficiency spectrum confirms the experimental results. The excellent mechanical properties of the abalone shell endow the random laser with good stability. The random laser has potential applications in speckle-free imaging and probing nanoscale structural alterations.

Multi-line frequency up-conversions are realized in Cs vapor using 718.8 nm pumping laser resonating with the two-photon transition 62S1/2 → 82D5/2 of Cs atom. The pumping beam is converted into a beam including wavelengths of 361.2, 387.7, 455.7 and 621.5 nm. Experiments with collimated and focused pumping configurations are carried out and compared. Spectrum peak at 361.2 nm is strongest under collimated pumping condition, while 387.7 nm is strongest under focused pumping beam. The output beam under focused pumping is more stable than that under collimated pumping. Results in this work may be useful in laser frequency standard, beacon light, laser measuring and optics communications, etc.

Diffusion bonded joints of Ti alloys and Al alloys are widely applied in chemical, nuclear, aerospace industries. In the present study, TC4/Al thin film/1060 Al joints were bonded successfully by means of diffusion bonding under low temperature. The microstructure and mechanical properties of the joints were investigated by SEM,XRD and shear strength test. The results showed that the highest shear strength of TC4/Al thin film/1060 Al joints was 80.2 MPa. With the increasing of temperature, the shear strength increases firstly and then almost remains the same. Ti and Al elements diffused to each other in the bonding process and the intermetallic compounds can’t be found. The fracture of the joint had taken place in the 1060 Al/Al thin film rather than in the TC4/Al thin film and the fracture way of the joints was ductile fracture.

Stimulated Raman Scattering (SRS) is important method of laser frequency conversion. Optical frequency-comb is a special kind of SRS which output multiple Stokes beam simultaneously, and lasers with mutiple wavelength have broad applications. In this paper, the optical frequency-comb generated by SRS of CO2 is presented and the spectral range covers from 0.4 μm to 1.5 μm. Research also indicates that the characteristics of optical frequency-comb depends on the wavelength of pumping laser. For instance, the SRS photon conversion efficiency pumped by 1064 nm laser is high at 1248nm, 1510nm but that pumped by 532 nm laser is high at 574nm, 624nm 683nm. The different features are compared and analyzed by the use of the mechanism of four-wave mixing and the change of SRS gain coefficient with Stokes wavelength.

A blue random laser based on solid waveguide gain films with silver nanoparticles (NPs) and SiO2 NPs is demonstrated. Located surface plasmon resonance (LSPR) property and multiple scattering are proven playing an important role simultaneously.

After the multiphoton ionization of sodium-argon mixture, time-resolved atomic emission spectrum is used to experimentally study the unusual phenomenon of the obviously different broadening between Na D1 and D2 lines spectra. The primary reason for the unusual broadening of Na D2 line is that the spectral line of Ar I 588.9 nm overlays with Na D2 line (589.0 nm) after ionization, and the serious self-absorption on Na D2 line is the secondary reason. Although there is difference of population between 32P3/2 and 32P1/2 states, the experiment result demonstrates that the difference between Na D lines in radiation channel will not affect the broadening of spectral profile.

Using a fiber of that is 125 μm in diameter in rhodamine 6G ethanol solution, controllable multi- and single-whispering-gallery-mode (WGM) optofluidic lasers based on evanescent-wave-coupled gain are both available. With multi-mode WGM emission, lasing emission with almost pure TM (transverse magnetic) or almost TE (transverse electric) modes can be obtained when the pump laser has an electric field parallel (perpendicular) to the fiber axis, i.e., the polarization direction of output laser is the same as that of the pump laser. On the other hand, when the laser emission is single-mode, the TE output laser always emerges firstly above lasing threshold, then keeps TE mode while the pump laser’s intensity increases with polarization direction perpendicular to the fiber axis; on the contrary, TE emission will dwindle relatively, while the TM emission emerges and dominates the spectra, when the pump laser’s intensity increases with polarization parallel to the fiber axis. Our work proves that controlling the leakage of the evanescent wave from high-Q microcavities is crucial for both modes of lasing emission and its polarization.

Terahertz emitting and FWM (Four wave mixing) processes in 6P3/2→11DJ near-resonating pumped cesium vapor are studied in this work. Using a nanosecond 550 nm pump laser, collimated frequency converted lights around 557 nm and 563 nm are observed in cesium vapor. A detailed analysis shows that the frequency converted lights come from FWM processes driven by the pump laser and stimulated terahertz emissions in the frequency range of 1–7 THz. These stimulated terahertz emissions are generated by cesium atom SERS (stimulated electronic Raman scattering) or ASE (amplified spontaneous emission) under pumping. The terahertz emission iQEs (internal quantum efficiency) are estimated to be on the order of 1 E -3 ~ 1 E -2 as their lower limits. Results of this work will contribute to studies on atom FWM physics, terahertz light source and detector based on atom vapor.

We report the observation of the undocumented visible one-photon photoluminescence (PL) of single silver nanorods excited by 532 and 633 nm continuous wave lasers with single-nanoparticle spectroscopy. We attribute the PL of silver nanorods to the intraband transition excited hot-electron radiative decay. The PL of silver nanorods closely resembles the corresponding LSPR scattering spectrum, and both are dependent on their aspect ratio. The good correlation between the quantitative PL intensity and the absorption cross section at the excitation wavelength of each nanorod leads to an aspect ratio independent PL quantum yield. The PL quantum yield of silver nanorods is similar to that of gold nanorods (10–6), indicating an efficient intraband excitation of hot electrons. The understanding of the PL mechanism of Ag nanorods points to the high-energy nature of the hot electrons excited via intraband transition, which has important indications in utilizing hot electrons for energy harvesting and photocatalysis.

Surface-enhanced Raman spectroscopy (SERS) has attracted tremendous interest as a label-free highly sensitive analytical method. For optimization of SERS activity, it is highly important to systematically investigate the size effect of nanoparticles on the SERS enhancement, which appears to be challenging in experiment, as the localized surface plasmon resonance (LSPR) of nanoparticles also changes with the change of the particle size. This challenge can be overcome by utilizing the unique property of gold nanorods, whose LSPR wavelength can be controlled to be the same by properly choosing the size and aspect ratio of the nanorods. We obtained the correlated SEM images, scattering spectra, and SERS spectra on a home-built single nanoparticle spectroscopy system and systematically investigate the size effect on SERS of individual gold nanorods using the adsorbed malachite green isothiocyanate (MGITC) molecule as the probe molecule. The dark field scattering intensity was found to increase with the increas...