Charged Quantum Dots Research Articles

Singlet oxygen generation by nanoassemblies containing porphyrin macrocycles: Steric and screening effects, energy transfer and competing processes

In this semi-review paper, we discuss some principal aspects that should be taken into account upon quantitative analysis of the interaction with molecular oxygen O2 and the singlet oxygen (1O2 or [Formula: see text] generation by various tetrapyrrolic photosensitizers (including monomers, chemical dimers, triads, pentads and organic-inorganic nanoassemblies). In all cases, the direct experimental measurements of 1O2 emission at [Formula: see text] = 1.27 μ need to be corrected to the solvent influence (refractive indexes, molecular polarizability) on the rate constant of the radiative transition [Formula: see text] in a 1O2 molecule. For porphyrin and chlorin chemical dimers, T1 states quenching by O2 followed by 1O2 generation depends on donor-acceptor interactions between the dimer halves, and extra-ligation effects as well as the spacer flexibility. In the case of self-assembled triads and pentads containing Zn-porphyrin dimers and pyridyl substituted porphyrin free bases (H2P) as extra-ligands, quenching rate constants of H2P T1 states by O2 are smaller compared to those found for individual monomeric H2P molecules which is explained by the spatial screening influence of a strongly quenched Zn-porphyrin dimer in multiporphyrin complexes. Finally, at 293 K for nanoassemblies of two types (semiconductor quantum dots CdSe/ZnS + coordinative linked tetra-pyridyl porphyrins, and semiconductor negatively charged quantum dots AgInS/ZnS + positively charged porphyrin molecules) it was quantitatively shown that non-radiative energy transfer FRET quantum dot [Formula: see text] porphyrin (competing with electron tunneling under conditions of quantum confinement) is only responsible for the singlet oxygen 1O2 generation by nanoassemblies.

Birefringent Spin‐Photon Interface Generates Polarization Entanglement

AbstractA spin‐photon interface based on the luminescence of a singly charged quantum dot in a micropillar cavity allows for the creation of photonic entangled states. Current devices suffer from cavity birefringence, which limits the generation of spin‐photon entanglement. In this study, we conduct a theoretical analysis of the light absorption and emission by the interface with an anisotropic cavity and derive the maximal excitation and spin‐photon entanglement conditions. It is shown that the concurrence of the spin‐photon state equal to one and complete quantum dot population inversion can be reached for a micropillar cavity with any degree of birefringence by tuning the quantum dot resonance strictly between the cavity modes. This sweet spot is also valid for generating a multiphoton cluster state, as demonstrated by calculating the three‐tangle and fidelity with the maximally entangled state.

Role of charge in enhanced nuclear transport and retention of graphene quantum dots

The nuclear pore complexes on the nuclear membrane serve as the exclusive gateway for communication between the nucleus and the cytoplasm, regulating the transport of various molecules, including nucleic acids and proteins. The present work investigates the kinetics of the transport of negatively charged graphene quantum dots through nuclear membranes, focusing on quantifying their transport characteristics. Experiments are carried out in permeabilized HeLa cells using time-lapse confocal fluorescence microscopy. Our findings indicate that negatively charged graphene quantum dots exhibit rapid transport to the nuclei, involving two distinct transport pathways in the translocation process. Complementary experiments on the nuclear import and export of graphene quantum dots validate the bi-directionality of transport, as evidenced by comparable transport rates. The study also shows that the negatively charged graphene quantum dots possess favorable retention properties, underscoring their potential as drug carriers.

Quantum paraelectric varactors for radiofrequency measurements at millikelvin temperatures

Radiofrequency reflectometry can provide fast and sensitive electrical read-out of charge and spin qubits in quantum dot devices coupled to resonant circuits. In situ frequency tuning and impedance matching of the resonator circuit using voltage-tunable capacitors (varactors) is needed to optimize read-out sensitivity, but the performance of conventional semiconductor- and ferroelectric-based varactors degrades substantially in the millikelvin temperature range relevant for solid-state quantum devices. Here we show that strontium titanate and potassium tantalate, materials which can exhibit quantum paraelectric behaviour with large field-tunable permittivity at low temperatures, can be used to make varactors with perfect impedance matching and resonator frequency tuning at 6 mK. We characterize the varactors at 6 mK in terms of their capacitance tunability, dissipative losses and magnetic field insensitivity. We use the quantum paraelectric varactors to optimize the radiofrequency read-out of carbon nanotube quantum dot devices, achieving a charge sensitivity of 4.8 μe Hz−1/2 and a capacitance sensitivity of 0.04 aF Hz−1/2.

High-performance zinc-ion hydrogel electrolytes based on molecular-level hybridization of PVA with polymer quantum dots

Aqueous zinc ion batteries have received widespread attention. However, the growth of zinc dendrites and hydrogen evolution reaction generation seriously hinder the practical application of zinc ion batteries. Herein, it is reported that a multifunctional dendrites-free low-temperature PVA-based gel electrolyte by introducing negatively charged polymer carbon quantum dots (QDs) and the organic antifreeze dimethyl sulfoxide (DMSO) into it. The QDs carrying a large number of functional groups on the surface can effectively adsorb Zn2+, eliminating the “tip effect”, and inducing the uniform deposition of Zn2+ and the formation of a dendrites-free structure. Meanwhile, the solvation structure of adsorbed Zn2+ can be controlled by charged groups to reduce the generation of side reactions, thus obtaining high-performance zinc ion batteries. The Zn/polyaniline (PANi) full battery can be stably cycled more than 1000 times at –20 °C, and the design of this gel electrolyte can provide good feasibility for safe, stable, and flexible energy storage devices.

Simultaneous monitoring of competing photo-induced weathering processes in colloidal CdSe/ZnS semiconductor quantum dots using multivariate frequency-domain dynamic photoluminescence measurements

Coincident photo-induced weathering processes in oleic acid capped CdSe/ZnS semiconductor quantum dots (QDs), stimulated by exposure to artificial sunlight in samples with different headspace volumes, were monitored using multichannel frequency-domain photoluminescence (PL) decay measurements. The combination of process monitoring using matrix-formatted measurements and multivariate data mining permits resolution of the spectra, frequency-domain decays and kinetic profiles of the PL emitted by distinct QD subpopulations. The data indicate that three components contribute to the PL: photodarkened QDs that emit bluer, shorter-lived spectra reflecting photoionization-induced QD charging and ligand desorption; photobrightened QDs that emit redder, short-lived spectra indicative of photooxidative QD surface passivation; and photoripened QDs that emit weak, red-shifted, large bandwidth, very long-lived spectra reflecting increasing nanoparticle growth and polydispersity. Analysis of the kinetic traces of the QD subpopulations during photoirradiation using systems of exponentials revealed the extent of coupling between the coincident photoinduced processes. The assignment of these components was supported by their emission maxima, spectral bandwidths, average and irradiation-time specific PL decay times, irradiation-dependent kinetic profiles, TEM images and literature precedents. As expected, the results show that QD photodarkening is faster and photobrightening is slower in the samples that have more exposure to water and oxygen. They also show that the dominant photodarkening and photobrightening pathways in those samples are not as strongly coupled, indicating the importance of contributions by additional processes in that case. Transmission electron microscopy (TEM) images were consistent with the PL results, but the QD samples proved too polydisperse to be characterized by single-beam dynamic light scattering measurements.

Uv–vis spectroscopy for simple chloride content analysis in edible oil using charged amino-functionalized carbon quantum dots fluorophore reagent

The utilization of UV–Vis spectroscopy with amino-functionalized carbon quantum dots (NCQD) as a positive fluorophore reagent for chloride sensing in oil marks a notable advancement in analytical spectroscopy chemistry. This approach streamlines the detection process by eliminating the need for lengthy procedures and pretreatment steps typically associated with chloride detection in edible oil. By incorporating NCQD in chloride detection within the oil matrix, the wavelength analysis transitions from the UV to the visible region. This shift eliminates interference from oil matrix interactions, ensuring more accurate results. Molecular analysis of NCQD reveals significant shifts in its Fourier Transformation Infrared and photoluminescence spectroscopy peaks due to interaction with chloride in edible oil. It has two impressive sensitivity ranges spanning from 0.1–1.0 to 1.0–8.0 ppm, with a value of −0.4656 au. ppm−1 (R2 = 0.998) and −0.0361 au. ppm−1 (R2 = 0.931), respectively, the technique meets regulatory standards while achieving a low limit of detection (LOD) of 0.1 ppm. This places it on par with conventional methods and commercial sensors. The NCQD-UV–Vis spectroscopy method not only enhances the efficiency and accuracy of chloride detection but also holds promise for various industrial applications requiring simple and precise monitoring of chloride levels in oil samples.

Size-dependent photoluminescence blinking mechanisms and volume scaling of biexciton Auger recombination in single CsPbI3 perovskite quantum dots.

Determining the correlation between the size of a single quantum dot (QD) and its photoluminescence (PL) properties is a challenging task. In the study, we determine the size of each QD by measuring its absorption cross section, which allows for accurate investigation of size-dependent PL blinking mechanisms and volume scaling of the biexciton Auger recombination at the single-particle level. A significant correlation between the blinking mechanism and QD size is observed under low excitation conditions. When the QD size is smaller than their Bohr diameter, single CsPbI3 perovskite QDs tend to exhibit BC-blinking, whereas they tend to exhibit Auger-blinking when the QD size exceeds their Bohr diameter. In addition, by extracting bright-state photons from the PL intensity trajectories, the effects of QD charging and surface defects on the biexcitons are effectively reduced. This allows for a more accurate measurement of the volume scaling of biexciton Auger recombination in weakly confined CsPbI3 perovskite QDs at the single-dot level, revealing a superlinear volume scaling (τXX,Auger ∝ σ1.96).

Absorption and Fluorescence Emission Investigations on Supramolecular Assemblies of Tetrakis-(4-sulfonatophenyl)porphyrin and Graphene Quantum Dots.

The one-pot synthesis of N-doped graphene quantum dots (GQDs), capped with a positively charged polyamine (trien), has been realized through a microwave-assisted pyrolysis on solid L-glutamic acid and trien in equimolar amounts. The resulting positively charged nanoparticles are strongly emissive in aqueous solutions and are stable for months. The interaction with the anionic tetrakis(4-sulphonatophenyl)porphyrin (TPPS4) has been investigated at neutral and mild acidic pH using a combination of UV/vis absorption spectroscopy together with static and time-resolved fluorescence emission. At pH = 7, the experimental evidence points to the formation of a supramolecular adduct mainly stabilized by electrostatic interactions. The fluorescence emission of the porphyrin is substantially quenched while GQDs remain still emissive. On decreasing the pH, protonation of TPPS4 leads to formation of porphyrin J-aggregates through the intermediacy of the charged quantum dots.

Precise Layer-by-Layer Assembly of Dual Quantum Dots Artificial Photosystems Enabling Solar Water Oxidation.

Quantum dots (QDs) colloidal nanocrystals are attracting enduring interest by scientific communities for solar energy conversion due to generic physicochemical merits including substantial light absorption coefficient, quantum confinement effect, enriched catalytically active sites, and tunable electronic structure. However, photo-induced charge carriers of QDs suffer from ultra-short charge lifespan and poor stability, rendering controllable vectorial charge modulation and customizing robust and stable QDs artificial photosystems challenging. Herein, tailor-made oppositely charged transition metal chalcogenides quantum dots (TMCs QDs) and MXene quantum dots (MQDs) are judiciously harnessed as the building blocks for electrostatic layer-by-layer assembly buildup on the metal oxides (MOs) framework. In these exquisitely designed LbL assembles MOs/(TMCs QDs/MQDs)n heterostructured photoanodes, TMCs QDs layer acts as light-harvesting antennas, and MQDs layer serves as electron-capturing mediator to relay cascade electrons from TMCs QDs to the MOs substrate, thereby yielding the spatially ordered tandem charge transport chain and contributing to the significantly boosted charge separation over TMCs QDs and solar water oxidation efficiency of MOs/(TMCs QDs/MQDs)n photoanodes. The relationship between interface configuration and charge transfer characteristics is unambiguously unlocked, by which photoelectrochemical mechanism is elucidated. This work would provide inspiring ideas for precisely mediating interfacial charge transfer pathways over QDs toward solar energy conversion.

Development of Fluorescent Sensors for Biorelevant Anions in Aqueous Media Using Positively Charged Quantum Dots.

Quantum dots (QDs) have captured the attention of the scientific community due to their unique optical and electronic properties, leading to extensive research for different applications. They have also been employed as sensors for ionic species owing to their sensing properties. Detecting anionic species in an aqueous medium is a challenge because the polar nature of water weakens the interactions between sensors and ions. The anions bicarbonate (HCO3-), carbonate (CO32-), sulfate (SO42-), and bisulfate (HSO4-) play a crucial role in various physiological, environmental, and industrial processes, influencing the regulation of biological fluids, ocean acidification, and corrosion processes. Therefore, it is necessary to develop approaches capable of detecting these anions with high sensitivity. This study utilized CdTe QDs stabilized with cysteamine (CdTe-CYA) as a fluorescent sensor for these anions. The QDs exhibited favorable optical properties and high photostability. The results revealed a gradual increase in the QDs' emission intensity with successive anion additions, indicating the sensitivity of CdTe-CYA to the anions. The sensor also exhibited selectivity toward the target ions, with good limits of detection (LODs) and quantification (LOQs). Thus, CdTe-CYA QDs show potential as fluorescent sensors for monitoring the target anions in water sources.

Electron–Electron and Electron–Phonon Interactions in the Dynamics of Trap-Filling in Charged Quantum Dots

Electron–Electron and Electron–Phonon Interactions in the Dynamics of Trap-Filling in Charged Quantum Dots

Hepatotoxicity evaluations of different surface charged carbon quantum dots in vivo and in vitro

Recently, carbon quantum dots (CQDs) have become popular because of their simple synthesis and potential applications. Although CQDs have high biocompatibility, their biotoxicity must be verified to reduce the possible risks associated with large-scale application. In this study, the hepatotoxicity of three CQD types, namely diammonium citrate (AC)-based (CQDs-AC), spermidine trihydrochloride (Spd)-based (CQDs-Spd), and AC- and Spd-based CQDs (CQDs-AC/Spd), were evaluated in vivo and in vitro. It was observed in vivo that CQDs-Spd and CQDs-AC/Spd, but not CQDs-AC, caused histopathological damage, including liver steatosis and mild mixed inflammatory cell infiltration; however, reduced liver function was only observed in CQD-Spd–treated mice. The in vitro results revealed that only CQDs-Spd significantly decreased the number of viable HepG2 cells (NADH depletion) and induced oxidative stress (heme oxygenase-1 activation) after 24 h of exposure, which promoted inflammatory factor secretion (NF-κB activation). Additionally, decreasing zonula occludens-2 and α1-antitrypsin protein expression in HepG2 cells suggested that CQD-Spd exposure increases the risk of liver diseases. Our results revealed that CQDs-Spd had greater hepatotoxic potential than CQDs-AC and CQDs-AC/Spd, which might be attributable to their high positive surface charge. Overall, the risk of CQD-induced hepatotoxic risk must be considered when applying positively charged CQDs.

Long-lived photon echo induced by nuclear spin fluctuations in charged InGaAs quantum dots

Long-lived photon echo induced by nuclear spin fluctuations in charged InGaAs quantum dots

Ground- and Excited-State Properties of Charged Non-Stoichiometric Quantum Dots

Ground- and Excited-State Properties of Charged Non-Stoichiometric Quantum Dots

Formation of vesicles between negatively charged carbon quantum dots and cationic surfactant cetylpyridinium chloride (CPC) due to oxidative photo induced electron transfer

The tuning of photo physical properties of highly emissive carbon quantum dots which was synthesized from citric acid in DMF medium through solvothermal method is investigated inside micelles formed by different types of surfactants like cationic surfactant cetylpyridinium chloride (CPC), cetrimonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS) and neutral surfactant polyethylene glycol tert-octyl phenyl ether (TX100), polyoxoethylene lauryl ether (BRIJ-35). Interestingly, only CPC interacts with greater extent and formed co-assembly with negatively-charged carbon quantum dots (CQDs) whereas other surfactants like CTAB, SDS, TX100 and BRIJ-35 do not alter the fluorescence intensity extensively. This results in the formation of a non fluorescent vesicle. No phase separation was observed over the large concentration barrier of the CPC surfactant. However, no such vesicle formation takes place for another cationic surfactant CTAB excluding the role of only electrostatic interaction. The synthesized vesicle is characterized by various techniques including HRTEM, DLS. For the aqueous solution of CQDs having concentration of 0.5 mg/ml, addition of CPC leads to formation of different sized vesicles of size 40 nm to 100 nm. The driving force behind this formation of non-fluorescent vesicles is oxidative photo induced electron transfer which is revealed by the highest occupied molecular orbital (HOMO) –lowest unoccupied molecular orbital (LUMO) interaction between the donor (CQDs) and the acceptor (CPC). We trust such type vesicle can be a suitable alternative for drug carriers, biomarkers and other various applications also.

Unraveling Mechanisms of Highly Efficient Yet Stable Electrochemiluminescence from Quantum Dots.

With CdSe/CdS/ZnS core/shell/shell quantum dots (QDs) as the model system, time- and potential-resolved spectroelectrochemical measurements are successfully applied for studying the general mechanisms and kinetics of electrochemiluminescence (ECL) generation. The rate constant of electron injection from the cathode into a QD to form a negatively charged QD (QD-) increases monotonically from -0.88 V to -1.2 V (vs Ag/AgCl). Mainly due to the deep LUMO of the QDs, the resulting QD- as the key intermediate for ECL generation is structurally stable and possesses very slow spontaneous deionization channels. The latter (the main non-ECL channels) are usually 3-4 orders of magnitude slower than the rate constant of the successive hole injection from an active co-reactant into a QD-. The kinetic studies quantify the internal ECL quantum yield of ideal QD ECL emitters to be nearly identical to that of photoluminescence, which is near unity for the current system. Identification of the key intermediate, discovery of the related elementary steps, and determination of all rate constants not only establish a general framework for understanding ECL generation but also offer basic design rules for ECL emitters.

Quadrupole assisted optical rectification and corresponding refractive index change in GaAs quantum dot in THz range

We investigate the optical rectification (OR) process and the corresponding refractive index change (RIC) in single electron charged GaAs spherical quantum dot. The effective mass approximation is used with the finite potential including the effect of conduction band nonparabolicity. The OR and the RIC processes are studied including dipole plus quadrupole effects within the framework of the density matrix approach for different dot radii and outside arsenide, nitride and oxide matrix in the terahertz range.

Charge Oscillations in Bilayer Graphene Quantum Confinement Devices.

Quantum confinement structures are building blocks of quantum devices in fundamental physics exploration and technological applications. In this work, we fabricate dual-gated bilayer graphene Fabry-Pérot quantum Hall interferometers employing two different gating strategies and conduct finite element simulations to understand the electrostatics of the confinement structures and to guide device design and fabrication. We observe two types of resistance oscillations arising from the charging of quantum dots formed inside the interferometers. We obtain the size, location, and charging energy of the dots by measuring the dependence of the oscillations on the magnetic field, gate voltages, and dc bias. We analyze and discuss the origin of the quantum dots and their impact on quantum Hall edge state backscattering and interference. Insights gained in these studies shed light on the construction of van der Waals quantum confinement devices.

Tuning Arrays with Rays: Physics-Informed Tuning of Quantum Dot Charge States

Tuning Arrays with Rays: Physics-Informed Tuning of Quantum Dot Charge States