Coupled Dots Research Articles

Enhanced oxygen evolution reaction performance of flower-like CoHS @NCDs through in-situ coupling of Nitrogen-Doped carbon dots and cobalt hydroxide nanosheets

Enhanced oxygen evolution reaction performance of flower-like CoHS @NCDs through in-situ coupling of Nitrogen-Doped carbon dots and cobalt hydroxide nanosheets

VN Quantum Dots Anchored onto Carbon Nanofibers as a Superior Anode for Sodium Ion Storage.

Vanadium-based compounds exhibit a high theoretical capacity to be used as anode materials in sodium-ion batteries, but the volume change in the active ions during the process of release leads to structural instability during the cycle. The structure of carbon nanofibers is stable, while it is difficult to deform. At the same time, the huge specific surface area energy of quantum dot materials can speed up the electrochemical reaction rate. Here, we coupled quantum-grade VN nanodots with carbon nanofibers. The strong coupling of VN quantum dots and carbon nanofibers makes the material have a network structure of interwoven nanofibers. Secondly, the carbon skeleton provides a three-dimensional channel for the rapid migration of sodium ions, and the material has low charge transfer resistance, which promotes the diffusion, intercalation and release of sodium ions, and significantly improves the electrochemical activity of sodium storage. When the material is used as the anode material in sodium ion batteries, the specific capacity is stable at 230.3 mAh g-1 after 500 cycles at 0.5 A g-1, and the specific capacity is still maintained at 154.7 mAh g-1 after 1000 cycles at 2 A g-1.

Se–S bonded non-metal elementary substance heterojunction activating photoelectrochemical water splitting

Non-metal elements are often merely regarded as electronic modulators, yet their intrinsic characteristics are frequently overlooked. Indeed, non-metal elements possess notable advantages in high-abundance, excellent hydrogen adsorption and the ability of active sites to be inversely activated, rendering them potential photoelectrochemical (PEC) materials. However, weak non-metal interbinding, susceptibility to photocorrosion, and high photogenerated carrier recombination rates hinder their practical applications. Herein, for the first time, we report a novel non-metal elementary substance heterojunction Se/S based on interfacial bonding engineering strategy. Atomic-level tight coupling of sulfonyl-rich sulfur quantum dots (SQDs) with selenium microtube arrays (Se-MTAs) enhances the structural stability of Se/S and introduces crucial Se–S heterointerfacial bonds, which not only endow Se/S with robust internal electronic interactions, but also provide high-speed channels for charge separation via unique bridging. Consequently, Se/S achieves optimal photocurrent density of 3.91 mA cm−2 at 0 VRHE, accompanied by long-term stability over 24 h. It is the highest value reported to date for Se-based photocathodes without co-catalyst and outperforms most metal-selenide-based photoelectrodes. Furthermore, the direct Z-scheme charge transport mechanism is exposed by in-depth spectroscopic analyses. Our work fills the gap in application of non-metal elementary substance heterojunction for PEC, poised for potential expansion into other new-energy devices.

Surface Engineering Enables Efficient AgBiS2 Quantum Dot Solar Cells.

Surface ligand chemistry is vital to control the synthesis, diminish surface defects, and improve the electronic coupling of quantum dots (QDs) toward emerging applications in optoelectronic devices. Here, we successfully develop highly homogeneous and dispersed AgBiS2 QDs, focus on the control of interdot spacing, and substitute the long-chain ligands with ammonium iodide in solution. This results in improved electronic coupling of AgBiS2 QDs with excellent surface passivation, which greatly facilitates carrier transport within the QD films. Based on the stable AgBiS2 QD dispersion with the optimal ligand state, a homogeneous and densely packed QD film is prepared by a facile one-step coating process, delivering a champion power conversion efficiency of approximately 8% in the QD solar cells with outstanding shelf life stability. The proposed surface engineering strategy holds the potential to become a universal preprocessing step in the realm of high-performance QD optoelectronic devices.

The synergistic effect of Cl doping and Bi coupling to promote the carrier separation of BiOBr for efficient photocatalytic nitrogen reduction

Photocatalytic nitrogen reduction reaction (NRR) is a sustainable process for ammonia synthesis under mild conditions. However, photocatalytic NRR activity and are generally limited by inefficient carrier separation and transfer. Therefore, parallel engineering of bulk phase doping and surface coupling is critical to achieving the goal of efficient NRR. In this study, Cl doped BiOBr nanosheet assemblies (BiOBr/Cl) were constructed in delicately designed deep eutectic solvents (DESs), combined with ionothermal methods at low temperatures and Bi3+ exsolution reduction strategy at high temperatures. The unique liquid state and reducibility of DESs induce the reduction of Bi3+ and the in situ coupling of Bi quantum dots at the surface of BiOBr/Cl nanosheets along with the construction of Bi-BiOBr/Cl nanosheet assemblies. The experimental results show that Cl doping could reduce the exciton dissociation energy and promote its dissociation to free carriers. Bi quantum dots could form tightly coupled Schottky junction with BiOBr/Cl enabling the efficient and unidirectional transmission of photogenerated electrons from BiOBr/Cl to metal Bi. The formed electron deficient region at Schottky interface promotes the adsorption and activation of N2. The hierarchical structure of Bi-BiOBr/Cl nanosheet assembly benefits to providing more N2 adsorption active sites. The DFT calculation shows that the accumulation of high concentration of active hydrogen in Bi-BiOBr/Cl leads to a significant decrease of energy barrier of the first step hydrogenation of N2. Bi-BiOBr/Clis more inclined to adsorb nitrogen for NRR in comparison with H* for hydrogen production. The synergistic effect of Cl doping and Bi coupling result in a high NRR activity of Bi-BiOBr/Cl photocatalyst of 6.67 mmol·g−1·h−1, which was 11.3 times higher than that of initial BiOBr. This study provides a promising strategy for designing highly active NRR photocatalysts with high efficiency carrier dissociation and transport.

Slow Hot-Exciton Cooling and Enhanced Interparticle Excitonic Coupling in HgTe Quantum Dots.

Rapid hot-carrier/exciton cooling constitutes a major loss channel for photovoltaic efficiency. How to decelerate the hot-carrier/exciton relaxation remains a crux for achieving high-performance photovoltaic devices. Here, we demonstrate slow hot-exciton cooling that can be extended to hundreds of picoseconds in colloidal HgTe quantum dots (QDs). The energy loss rate is 1 order of magnitude smaller than bulk inorganic semiconductors, mediated by phonon bottleneck and interband biexciton Auger recombination (BAR) effects, which are both augmented at reduced QD sizes. The two effects are competitive with the emergence of multiple exciton generation. Intriguingly, BAR dominates even under low excitation fluences with a decrease in interparticle distance. Both experimental evidence and numerical evidence reveal that such efficient BAR derives from the tunneling-mediated interparticle excitonic coupling induced by wave function overlap between neighboring HgTe QDs in films. Thus, our study unveils the potential for realizing efficient hot-carrier/exciton solar cells based on HgTe QDs. Fundamentally, we reveal that the delocalized nature of quantum-confined wave function intensifies BAR. The interparticle excitonic coupling may cast light on the development of next-generation photoelectronic materials, which can retain the size-tunable confinement of colloidal semiconductor QDs while simultaneously maintaining high mobilities and conductivities typical for bulk semiconductor materials.

Stronger Coupling of Quantum Dots in Hole Transport Layer Through Intermediate Ligand Exchange to Enhance the Efficiency of PbS Quantum Dot Solar Cells.

Nowadays, the extensively used lead sulfide (PbS) quantum dot (QD) hole transport layer (HTL) relies on layer-by-layer method to replace long chain oleic acid (OA) ligands with short 1,2-ethanedithiol (EDT) ligands for preparation. However, the inevitable significant volume shrinkage caused by this traditional method will result in undesired cracks and disordered QD arrangement in the film, along with adverse increased defect density and inhomogeneous energy landscape. To solve the problem, a novel method for EDT passivated PbS QD (PbS-EDT) HTL preparation using small-sized benzoic acid (BA) as intermediate ligands is proposed in this work. BA is substituted for OA ligands in solution followed by ligand exchange with EDT layer by layer. With the new method, smoother PbS-EDT films with more ordered and closer QD packing are gained. It is demonstrated stronger coupling between QDs and reduced defects in the QD HTL owing to the intermediate BA ligand exchange. As a result, the suppressed nonradiative recombination and enhanced carrier mobility are achieved, contributing to ≈20% growth in short circuit current density (Jsc) and a 23.4% higher power conversion efficiency (PCE) of 13.2%. This work provides a general framework for layer-by-layer QD film manufacturing optimization.

In situ coupling of carbon dots with zeolitic imidazolate frameworks enabling highly red emission in solid state

In this work, an extraordinary solid red emissive phosphor was prepared based on red-emitting carbon dots (R-CDs). The synthesis was conducted under an in-situ strategy, with assistance of zeolitic imidazolate frameworks. The obtained phosphor possesses a stronger red emission located at 630 nm in solid state, with CIE coordinate of (0.63, 0.35) and quantum yield of ∼ 45 %. As a consequence, not only aggregation-induced fluorescence quenching of R-CDs is avoided in solid state, but also an enhanced emission with high quantum yield is presented. Fluorescence properties were further explored in detail. The emission is found to be responsive to temperature and applied pressure. Based on the excellent emissive performance, the material has great potentials in anti-counterfeiting, latent fingerprint imaging, and temperature/pressure-sensing. This work provides a facile and promising way of preparing solid carbon-based phosphors for special applications.

Portable tri-color ratiometric fluorescence paper sensor for intelligent visual detection of dual-antibiotics and aluminium ion

The toxicological effect between co-existed antibiotics and metal ions was dangerous to the ecological environment and public health. However, the rapid quantification tools with convenience, accuracy and low cost for the detection of multiple targets were still challenging. Herein, a portable tri-color ratiometric fluorescence paper sensor was constructed by coupling of blue carbon dots and fluorescence imprinted polymer for down/up conversion simultaneous detection of tetracycline and sulfamethazine. Interestingly, the cascade detection of aluminum ion was also realized based on the individual detection system of tetracycline without the assistance of complex coupling reagents. The detection limits of smartphone method for the visual detection of tetracycline, sulfamethazine and aluminum ion were calculated as 0.014 μM, 0.004 μM and 0.019 μM, respectively. The portable fluorescence paper sensor was applied for the visual detection of tetracycline, sulfamethazine and aluminum ion in actual samples successfully with satisfactory recoveries. With the advantages of rapidness, low cost, and portability, the developed portable fluorescence paper sensor provided a new strategy for the visual real-time detection of multiple targets.

Both enhancement and strong coupling of quantum dots on asymmetric Fabry-Perot cavity at room temperature

Abstract The interaction of light and matter is an eternal theme in optics and optoelectronics. Until now, there is almost no report about realization of both strong coupling and enhancement simultaneously. In this study, the angle-resolved photoluminescence spectra of colloidal quantum dots on the surface of SiO2/Si material are investigated. When the PL spectrum peak overlaps with the Fabry–Perot (F-P) mode of SiO2 film, the PL spectrum near emission wavelength of bare colloidal quantum dots splits into two peaks, which is Rabi splitting. Moreover, a huge enhancement factor is obtained for the PL spectra in the short-wavelength region. Both extremely huge enhancement and large Rabi splitting are obtained with colloidal quantum dots coupled low-refractive-index/high-refractive-index dielectric material system.

Spin-photon interaction in a nanowire quantum dot with asymmetrical confining potential

The electron (hole) spin–photon interaction is studied in an asymmetrical InSb (Ge) nanowire quantum dot. The spin–orbit coupling in the quantum dot mediates not only a transverse spin–photon interaction, but also a longitudinal spin–photon interaction due to the asymmetry of the confining potential. Both the transverse and the longitudinal spin–photon interactions have non-monotonic dependence on the spin–orbit coupling. For realistic spin–orbit coupling in the quantum dot, the longitudinal spin–photon interaction is much (at least one order) smaller than the transverse spin–photon interaction. The order of the transverse spin–photon interaction is about 1 nm in terms of length |zeg| , or 0.1 MHz in terms of frequency eE0|zeg|/h for a moderate cavity electric field strength E0=0.4 V m−1.

An Exact Expression for Multidimensional Spectroscopy of a Spin‐Boson Hamiltonian

AbstractMultidimensional coherent spectroscopy is a powerful tool to characterize nonlinear optical response functions. Typically, multidimensional spectra are interpreted via a perturbative framework that straightforwardly provides intuition into the density matrix dynamics that give rise to specific spectral features. When the goal is to characterize system coupling to a thermal bath however, the perturbative formalism becomes unwieldy and yields less intuition. Here, an approach developed by Vagov et al. is extended to provide an exact expression for multidimensional spectra of a spin‐boson Hamiltonian up to arbitrary order of electric field interaction. The utility of this expression is demonstrated by modeling polaron formation and coherent exciton‐phonon coupling in quantum dots, which strongly agree with experiment.

Chiral Majorana fermions resonance exchange moudulated by quantum dot coupling strength

We study the resonance exchanges of two chiral Majorana fermions in two distinct systems theoretically in this work: one is an isolated Majorana zero mode interacting with complexes formed by two chiral Majorana fermions and a Majorana zero mode, and the other involves isolated quantum dots that are coupled to a system composed of Majorana fermions and a quantum dot. Our research results reveal that both of these coupled systems can facilitate the effective transmissions of the two chiral Majorana fermions as <inline-formula><tex-math id="M1">\begin{document}$ {\gamma _1} \to - {\gamma _2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M1.png"/></alternatives></inline-formula>and <inline-formula><tex-math id="M2">\begin{document}$ {\gamma _2} \to - {\gamma _1} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M2.png"/></alternatives></inline-formula>, and the resonant tunneling effects in the two systems are equivalent. Therefore, quantum dots can replace Majorana zero modes to achieve resonant tunneling. In order to observe the resonance exchange of two chiral Majorana fermions with the two quantum dots, a circuit based on anomalous quantum Hall insulator proximity-coupled with s-wave superconductor is proposed as shown in figure. The numerical results indicate that the resonant exchange of chiral Majorana fermions can be modulated by the coupling strength between the two quantum dots, and it is particularly noteworthy that the tunneling process is independent of the superconducting phase. If one of the chiral Majorana fermions undergoes resonance coupling with another quantum dot or Majorana zero mode, an additional negative sign is obtained, leading to <inline-formula><tex-math id="M3">\begin{document}$ - {\gamma _2} \to {\gamma _1} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M3.png"/></alternatives></inline-formula>. After experiencing two resonance exchange processes, the final result is <inline-formula><tex-math id="M4">\begin{document}$ {\gamma _1} \to {\gamma _2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M4.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M5">\begin{document}$ {\gamma _2} \to - {\gamma _1} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M5.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M5.png"/></alternatives></inline-formula>, which implies the realization of non-Abelian braiding operations. Our conclusion is that the modulation of coupling strength between two quantum dots can be used to achieve the switch of Majorana fermions braiding-like operation, which is independent of superconducting phase. Therefore, the designed scheme provides a new way for adjusting the braiding-like operation of Majorana fermions. These findings may have potential applications in the realization of topological quantum computers.

Light-Driven Metabolic Pathways in Non-Photosynthetic Biohybrid Bacteria.

Biomanufacturing via microorganisms relies on carbon substrates for molecular feedstocks and a source of energy to carry out enzymatic reactions. This creates metabolic bottlenecks and lowers the efficiency for substrate conversion. Nanoparticle biohybridization with proteins and whole cell surfaces can bypass the need for redox cofactor regeneration for improved secondary metabolite production in a non-specific manner. Here we propose using nanobiohybrid organisms (Nanorgs), intracellular protein-nanoparticle hybrids formed through the spontaneous coupling of core-shell quantum dots (QDs) with histidine-tagged enzymes in non-photosynthetic bacteria, for light-mediated control of bacterial metabolism. This proved to eliminate metabolic constrictions and replace glucose with light as the source of energy in Escherichia coli, with an increase in growth by 1.7-fold in 75 % reduced nutrient media. Metabolomic tracking through carbon isotope labeling confirmed flux shunting through targeted pathways, with accumulation of metabolites downstream of respective targets. Finally, application of Nanorgs with the Ehrlich pathway improved isobutanol titers/yield by 3.9-fold in 75 % less sugar from E. coli strains with no genetic alterations. These results demonstrate the promise of Nanorgs for metabolic engineering and low-cost biomanufacturing.

Carbon dots with full-color-tunable room-temperature phosphorescence for photo-stimulated responsive application

Advances in polymeric matrices with ultralong and color-tunable phosphorescence were recently made, but their luminescence mechanism was not yet thoroughly understood. The current experimental and theoretical studies show that the red-shift of phosphorescence spectrum is caused by increasing the C–N and C=O of carbon dots in the polymeric matrix. In addition, theoretical calculations explain the charge transfer and spin orbit coupling of carbon dots in a system containing different covalent bonds. The phosphorescence emission color and lifetime can be modulated, which is applied into triple anti-counterfeiting of photo-stimulated-dependent color, time-dependent color, and time-dependent phosphorescence lifetime. In the application, the phosphorescence color of carbon dots in the polymeric matrix can be varied from deep blue (431 nm) to red (620 nm) with a maximal lifetime of 2.02 s and a maximum phosphorescence quantum yield of 20.1%. This work provides a new direction for the development of carbon dots with efficient and color-tunable ultra-long phosphorescence.

In-situ coupling of N-doped carbon dots with manganese hexacyanoferrate as a cathode material for aqueous zinc-ion batteries

Prussian blue analogs (PBAs) are a competitive class of aqueous Zn-ion batteries (AZIBs) cathode materials with an ideal three-dimensional open structure for rapid insertion and removal of Zn2+. Meanwhile, PBAs have the advantages of high working voltage and a simple synthesis process. However, these materials are inherently poor in electrical conductivity and are susceptible to structural collapse during cycling. These defects affect the performance of zinc storage in this type of material. Here, the integration of zero-dimensional nitrogen-doped carbon dots (NCDs) and in-situ grown manganese hexacyanoferrate (MnHCF) affords the MnHCF/NCDs cathode materials, which are applied to AZIBs. The introduction of NCDs modifies the active component of MnHCF effectively. Meanwhile, NCDs significantly enhance the overall electrical conductivity and structural stability of the composites and also provide abundant active sites for electrochemical reactions. Benefiting from these merits, the MnHCF/NCDs composite exhibits an excellent electrochemical zinc storage performance. It has a high discharge-specific capacity of 131.2 mAh g−1 at 50 mA g−1 and has outstanding cycling stability of 91% capacity retention after 1000 cycles at 1000 mA g−1. The electrochemical performance of PBAs-based cathodes for AZIBs may be improved using the straightforward and efficient method presented in this work.

Offline Coupling of CdS Quantum Dots with Ion Mobility Spectrometry: Simultaneous Determination of Pantoprazole and Domperidone

Offline Coupling of CdS Quantum Dots with Ion Mobility Spectrometry: Simultaneous Determination of Pantoprazole and Domperidone

Identifying Pauli blockade regimes in bilayer graphene double quantum dots

Recent experimental observations of current blockades in 2D material quantum-dot platforms have opened new avenues for spin and valley-qubit processing. Motivated by experimental results, we construct a model capturing the delicate interplay of Coulomb interactions, inter-dot tunneling, Zeeman splittings, and intrinsic spin–orbit coupling in a double quantum dot (DQD) structure to simulate the Pauli blockades. Analyzing the relevant Fock-subspaces of the generalized Hamiltonian, coupled with the density matrix master equation technique for transport across the setup, we identify the generic class of blockade mechanisms. Most importantly, and contrary to what is widely recognized, we show that conducting and blocking states responsible for the Pauli-blockades are a result of the coupled effect of all degrees of freedom and cannot be explained using the spin or the valley pseudo-spin only. We then numerically predict the regimes where Pauli blockades might occur, and, to this end, we verify our model against actual experimental data and propose that our model can be used to generate data sets for different values of parameters with the ultimate goal of training on a machine learning algorithm. Our work provides an enabling platform for a predictable theory-aided experimental realization of single-shot readout of the spin and valley states on DQDs based on 2D-material platforms.

Interplay of Pauli blockade with electron-photon coupling in quantum dots

Both quantum transport measurements in the Pauli blockade regime and microwave cavity transmission measurements are important tools for spin-qubit readout and characterization. Based on a generalized input-output theory we derive a theoretical framework to investigate how a double quantum dot (DQD) in a transport setup interacts with a coupled microwave resonator while the current through the DQD is rectified by Pauli blockade. We show that the output field of the resonator can be used to infer the leakage current and thus obtain insight into the blockade mechanisms. In the case of a silicon DQD, we show how the valley quasidegeneracy can impose limitations on this scheme. We also demonstrate that a large number of unknown DQD parameters including (but not limited to) the valley splitting can be estimated from the resonator response simultaneous to a transport experiment, providing more detailed knowledge about the microscopic environment of the DQD. Furthermore, we describe and quantify a back action of the resonator photons on the steady-state leakage current.

Narrow Intrinsic Line Widths and Electron–Phonon Coupling of InP Colloidal Quantum Dots

InP quantum dots (QDs) are the material of choice for QD display applications and have been used as active layers in QD light-emitting diodes (QDLEDs) with high efficiency and color purity. Optimizing the color purity of QDs requires understanding mechanisms of spectral broadening. While ensemble-level broadening can be minimized by synthetic tuning to yield monodisperse QD sizes, single QD line widths are broadened by exciton-phonon scattering and fine-structure splitting. Here, using photon-correlation Fourier spectroscopy, we extract average single QD line widths of 50 meV at 293 K for red-emitting InP/ZnSe/ZnS QDs, among the narrowest for colloidal QDs. We measure InP/ZnSe/ZnS single QD emission line shapes at temperatures between 4 and 293 K and model the spectra using a modified independent boson model. We find that inelastic acoustic phonon scattering and fine-structure splitting are the most prominent broadening mechanisms at low temperatures, whereas pure dephasing from elastic acoustic phonon scattering is the primary broadening mechanism at elevated temperatures, and optical phonon scattering contributes minimally across all temperatures. Conversely for CdSe/CdS/ZnS QDs, we find that optical phonon scattering is a larger contributor to the line shape at elevated temperatures, leading to intrinsically broader single-dot line widths than for InP/ZnSe/ZnS. We are able to reconcile narrow low-temperature line widths and broad room-temperature line widths within a self-consistent model that enables parametrization of line width broadening, for different material classes. This can be used for the rational design of more spectrally narrow materials. Our findings reveal that red-emitting InP/ZnSe/ZnS QDs have intrinsically narrower line widths than typically synthesized CdSe QDs, suggesting that these materials could be used to realize QDLEDs with high color purity.