Bright Dots Research Articles

Glow-to-arc transition in graphite cathode with high-current magnetron discharge

The glow-to-arc transition is a critical phenomenon in plasma discharges, commonly leading to detrimental effects. The physical mechanisms triggering this transition remain poorly understood. The advent of a discharge called Hyper-Power Impulse Magnetron has opened possibilities. Hyper-Power Impulse Magnetron allows the glow mode to be maintained over long periods (1 ms) and at high-current densities (>5 A .cm−2), which has unveiled certain features in the glow-to-arc transition. This work focuses on a graphite target that transits easily in the arc regime. The high-speed video-camera analysis revealed specific properties of graphite in ExB discharges, and the statistical study of the arc transition revealed differences from other refractory target materials. The early stage of cathodic spot formation, observed as bright dots, will be presented and analyzed within the known “ecton” and “vaporization” models for spot formation. This experimental study highlights the role of luminous spot formation prior to arc transition, with possible optimization on the stability of magnetron discharges.

Dual Detection of Norfloxacin and Gatifloxacin by Excitation Tuning Strategy Based on Yellow Carbon Dots.

Fluoroquinolones (FQs) are widely used in hospitals, animal husbandry and aquaculture for the treatment of infectious diseases. However, overuse of FQs poses a potential threat to the environment and human. Detection of antibiotics is of great importance in various fields. In this paper, bright yellow fluorescence carbon dots (y-CDs) with quantum yield of 32% were synthesized via a simple and rapid microwave-assisted method using o-phenylenediamine and salicylic acid as raw materials. The fluorescence properties of y-CDs varied under different excitation wavelengths. It is discovered that the excitation wavelength is a critical factor to develop a dual functional fluorescence probe. Under selected excitation wavelength (355nm), y-CDs can realize dual detection of norfloxacin (NOR) and gatifloxacin (GAT) with good selectivity and high sensitivity in a "turn-on" mode. The detection limits of NOR and GAT are 0.0881 µM and 0.0125 µM, respectively. y-CDs prove practical application in the detection of NOR and GAT in milk and egg samples.

Purifying quantum-dot light in a coherent frequency interface

Abstract Quantum networks typically operate in the telecom wavelengths to take advantage of low-loss transmission in optical fibres. However, bright quantum dots (QDs) emitting highly indistinguishable quantum states of light, such as InGaAs QDs, often emit photons in the near infrared thus necessitating frequency conversion (FC) to the telecom band. Furthermore, the signal quality of quantum emissions is crucial for the effective performance of these networks. In this work we report a method for simultaneously implementing spectral purification and frequency shifting of single photons from QD sources to the c-band in a periodically poled lithium niobate waveguide. We consider difference frequency generation in the counter-propagating configuration to implement FC with the output emission bandwidth in units of GHz. Our approach establishes a clear path to integrating high-performance single-emitter sources in a hybrid quantum network.

Biocompatible bright orange emissive carbon dots: Multifunctional nanoprobes for highly specific sensing toxic Cr(VI) ions and mitochondrial targeting cancer cell imaging

Although several luminescent-based nanostructured materials are used as cellular imaging probes, creating a biocompatible subcellular imaging probe can be challenging. Instantaneously, it is crucial and urgently needed for certain fluorescent nanoprobes to identify possibly harmful heavy metal ions. We present a straightforward one-pot preparation of bright orange emissive (quantum yield approximately 16 %) Nitrogen/Sulfur co-doped carbon dots (N/S CDs) from citric acid and methylene blue as raw materials that will serve as a specific Cr(VI) ions sensor and an effective mitochondrial labeling in cancer cells. They had several benefits including low ecological impact, facile synthesis, good water solubility, photostability, and high stability. We found that N/S CDs photoluminescence (PL) could be reduced when Cr(VI) ions were present near them, and the PL reduction occurred highly sensitively to the presence of Cr(VI) compared to other metal ions including Cr(III) ions. This specific reduction of PL was due to the non-fluorescent complex formation through the inner filter effect (IFE). The established fluorescence-based sensing technique could serve for Cr(VI) ion quantification with exceptional sensing efficiency in the wide linear range of 7 to 70 μM (R2 = 0.9873), with the limit of detection of 53.5 nM. It was also revealed that the current fluorescent probe could be encouragingly utilized to quantify the concentration of Cr(VI) ions in various water specimens such as tap water. In addition, they were shown to function as a mitochondria-targeting nanoprobe in human cancer cells (ME 180 cells and Hela cells) for cell imaging. Concludingly, it was envisioned that these fluorescent nanoprobes could find a use in real-time monitoring of Cr(VI) ions in water-based ecosystems with ultrahigh sensitivity and cell image tracking via mitochondria labeling as biocompatible nanoprobes.

Bright yellow fluorescent carbon dots as selective nanoprobe for detection of 2-nitrophenol and 4-nitrophenol in aqueous medium

Different types of phenolic pollutants pose a major risk to the environment and the health of living things. It is therefore crucial for their selective recognition especially nitrophenols. In this work, yellow fluorescent carbon dots (C-dots) were used as selective nanoprobe to efficiently detect 2-nitrophenol (2-NP) and 4-nitrophenol (4-NP). One-pot synthetic method was adopted for making C-dots from o-phenylenediamine and oleic acid mixture. The synthesized C-dots showed an excitation wavelength of 420 nm with Stokes shift of up to 135 nm. These C-dots exhibited instantaneous selective detection of 2-NP and 4-NP in aqueous solution with a detection limit of 6.4 nM and 4.8 nM respectively. Upon incubated with 2-NP and 4-NP, the C-dots’ fluorescence underwent quenching with a maximum extent of respective 80 % and 83 %. By comparing with other analogs of analyte, it was discovered that the emission intensity of the C-dots remained unchanged. Static quenching was proposed behind the changes of fluorescence after the treatment with 2-NP and 4-NP. Such type of C-dots will demonstrate the selective sensing platform in real field application.

Fabrication and Efficient Interfacial Assembly of Bright Red-Emitting Carbon Quantum Dots for Security-Warning Textiles.

Carbon quantum dots (CQDs) have attracted more attentions due to their multiple performances. However, the fabrication of long-wavelength emitting CQDs with aliphatic precursors still remains a challenge, mainly because it is difficult to generate large sp2 domains to reduce energy gap, which is not conducive to a redshift of the luminescence peak. Hereon, by regulating the pH of citric acid and thiourea mixture, a N, S co-doped CQD emitting bright red fluorescence at 635nm is successfully fabricated through the solvothermal reaction under acidic condition, achieving a high quantum yield of 32.66%. Solvatochromic effects of the CQDs are discussed through theoretical equations and models, which confirm that the hydrogen-bonding interaction dominates the fluorescence emission behavior of CQDs in polar solvents. Besides, a feasible strategy is proposed to prepare an anti-counterfeiting textile via the deposition of red-emitting CQDs onto cotton fibers, through rapidly evaporating the preferred organic solvent. As expected, the CQD-decorated textiles exhibit encouraging anti-counterfeiting and security-warning functions, along with underwater and long-distance detectability, washability, and sun resistance. It is worth noting that the present work is innovative in realizing the application of red-light-emitting CQDs in the fields of security-warning textiles.

Mutant mice with rod-specific VPS35 deletion exhibit retinal α-synuclein pathology-associated degeneration

Vacuolar protein sorting 35 (VPS35), the core component of the retromer complex which regulates endosomal trafficking, is genetically linked with Parkinson’s disease (PD). Impaired vision is a common non-motor manifestation of PD. Here, we show mouse retinas with VPS35-deficient rods exhibit synapse loss and visual deficit, followed by progressive degeneration concomitant with the emergence of Lewy body-like inclusions and phospho-α-synuclein (P-αSyn) aggregation. Ultrastructural analyses reveal VPS35-deficient rods accumulate aggregates in late endosomes, deposited as lipofuscins bound to P-αSyn. Mechanistically, we uncover a protein network of VPS35 and its interaction with HSC70. VPS35 deficiency promotes sequestration of HSC70 and P-αSyn aggregation in late endosomes. Microglia which engulf lipofuscins and P-αSyn aggregates are activated, displaying autofluorescence, observed as bright dots in fundus imaging of live animals, coinciding with pathology onset and progression. The Rod∆Vps35 mouse line is a valuable tool for further mechanistic investigation of αSyn lesions and retinal degenerative diseases.

An investigation of quantum dot theranostic probes for prostate and leukemia cancer cells using a CdZnSeS QD-based nanoformulation

Anticancer theranostic nanocarriers have the potential to enhance the efficacy of pharmaceutical evaluation of drugs. Semiconductor nanocrystals, also known as quantum dots (QDs), are particularly promising components of drug carrier systems due to their small sizes and robust photoluminescence properties. Herein, bright CdZnSeS quantum dots were synthesized in a single step via the hot injection method. The particles have a quasi-core/shell structure as evident from the high quantum yield (85 %), which decreased to 41 % after water solubilization. These water solubilized QDs were encapsulated into gallic acid / alginate (GA-Alg) matrices to fabricate imaging QDs@mod-PAA/GA-Alg particles with enhanced stability in aqueous media. Cell viability assessments demonstrated that these nanocarriers exhibited viability ranging from 63 % to 83 % across all tested cell lines. Furthermore, the QDs@mod-PAA/GA-Alg particles were loaded with betulinic acid (BA) and ceranib-2 (C2) for in vitro drug release studies against HL-60 leukemia and PC-3 prostate cancer cells. The BA loaded QDs@mod-PAA/GA-Alg had a half-maximal inhibitory concentration (IC50) of 8.76 μg/mL against HL-60 leukemia cells, which is 3-fold lower than that of free BA (IC50 = 26.55 μg/mL). Similar enhancements were observed with nanocarriers loaded with C2 and simultaneously with both BA and C2. Additionally, BA:C2 loaded QDs@mod-PAA/GA-Alg nanocarriers displayed a similar enhancement (IC50 = 3.37 μg/mL compared against IC50 = 11.68 μg/mL for free BA:C2). The C2 loaded QDs@mod-PAA/GA-Alg nanocarriers had an IC50 = 2.24 μg/mL against HL-60 cells. C2 and BA loaded QDs@mod-PAA/GA-Alg NCr had IC50 values of 7.37 μg/mL and 24.55 μg/mL against PC-3 cells, respectively.

Water sensitized and highly bright multicolor Ni-doped carbon dots nanoarchitectonics in polar solvents towards stable flexible films

To address the issues of low photoluminescence quantum yields (PLQYs), broad PL spectra, and poor stability, multicolor carbon dots (CDs) were synthesized by using different precursors. Blue-emitting CDs were created via a solvothermal synthesis by using citric acid and ethylenediamine while green-emitting CDs were fabricated using O-phenylenediamine. Ni doping further increased the PLQYs and stability of CDs. Ni-doped CDs (Ni-CDs) with blue- and green-emitting were synthesized through a one-step solvothermal method. The PL peak wavelengths of Ni-doped blue CDs (Ni-BCDs) and Ni-doped green CDs (Ni-GCDs) were located at 450 and 540 nm, respectively. After Ni-doping, the average particle size of green-emitting CDs was increased from 2.35 to 2.65 nm. Compared with undoped CDs, Ni-CDs exhibited narrow PL spectra, high PLQYs, and long fluorescent lifetime. The PLQYs of Ni-BCDs and Ni-GCDs were increased to 83.92 and 35.60 %, respectively. Interestingly, the PL peak wavelengths of Ni-doped CDs revealed a red-shift with increasing the solvent polarity (e.g. acetone, acetonitrile, N, N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, ethanol, methanol, and H2O). In addition, the PL peaks of green-emitting Ni-CDs generated a large red-shift with increase the ratio of water in organic solvents compared with blue one. Namely, solid Ni-GCDs powders also revealed water dependent PL. After incorporating the CDs in flexible films, Ni-GCDs still revealed high brightness and stability. These results supplied important possibility for the application of multicolor CDs.

Vacuum-Boosting Precise Synthetic Control of Highly Bright Solid-State Carbon Quantum Dots Enables Efficient Light Emitting Diodes.

Carbon quantum dots (C-dots) have emerged as efficient fluorescent materials for solid-state lighting devices. However, it is still a challenge to obtain highly bright solid-state C-dots because of the aggregation caused quenching. Compared to the encapsulation of as-prepared C-dots in matrices, one-step preparation of C-dots/matrix complex is a good method to obtain highly bright solid-state C-dots, which is still quite limited. Here, an efficient and controllable vacuum-boosting gradient heating approach is demonstrated for in situ synthesis of a stable and efficient C-dots/matrix complex. The addition of boric acid strongly bonded with urea, promoting the selectivity of the reaction between citric acid and urea. Benefiting from the high reaction selectivity and spatial-confinement growth of C-dots in porous matrices, in situ synthesize C-dots bonded can synthesized dominantly with a crosslinked octa-cyclic compound, biuret and cyanuric acid (triuret). The obtained C-dots/matrix complex exhibited bright green emission with a quantum yield as high as 90% and excellent thermal and photo stability. As a proof-of-concept, the as-prepared C-dots are used for the fabrication of white light-emitting diodes (LEDs) with a color rendering index of 84 and luminous efficiency of 88.14lm W-1, showing great potential for applications in LEDs.

The "energy gap law" for mid-infrared nanocrystals.

Colloidal quantum dots are of increasing interest for mid-infrared detection and emission, but device performances will vastly benefit from reducing the non-radiative recombination. Empirically, the photoluminescence quantum yield decreases exponentially toward the mid-infrared, which appears similar to the energy gap law known for molecular fluorescence in the near-infrared. For molecules, the mechanism is electron-vibration coupling and fast internal vibrational relaxation. Here, we explore the possible mechanisms for inorganic quantum dots. The primary mechanism is assigned to an electric dipole near-field energy transfer from the quantum dot electronic transitions to the infrared absorption of surface organic ligands and then to the multiphonon absorption of the quantum dot inorganic core or the surrounding inorganic matrix. In order to obtain luminescent quantum dots in the 3-10μm range, we motivate the importance of using inorganic matrices, which have a higher infrared transparency compared to organic materials. At longer wavelengths, inter-quantum dot energy transfer is noted to be much faster than radiative relaxation, indicating that bright mid-infrared colloidal quantum dot films might then benefit from dilution.

Bright, Flexible, and Waterproof Top-Emitting InP Quantum Dot Light-Emitting Diodes on Al Foil

Bright, Flexible, and Waterproof Top-Emitting InP Quantum Dot Light-Emitting Diodes on Al Foil

Bright InP quantum dots by Ga-doping for red emitters

Bright InP quantum dots by Ga-doping for red emitters

Composition analysis of Magnolia flower and their use for highly bright carbon dots

Colloidal carbon dots (C-dots) have excellent optical properties and they have been widely used for various types of applications. Compared to the C-dots prepared using chemicals, the Biomass-derived C-dots have attracted a great of attention because of their environmental friendliness and biocompatibility. However, currently obtained C-dots using biomass have low quantum yield. In this work, we demonstrated an efficient precursor of Magnolia flower for synthesizing high-quantum yield C-dots via hydrothermal approach. High performance liquid chromatography and Bradford assay were used to analyze the compositions of the Magnolia flower, which determine the quality of the C-dots. The typical emission bands of the as-prepared C-dots cover from 400 to 550 nm at different excitation wavelengths. The C-dots synthesized using violet Magnolia flower have the QY as high as 11.9%, which is higher than that of 10.4% (white Magnolia flower), because the violet color gives the higher content of the N. The as-obtained C-dots have excitation-dependent color and high quantum yield, showing a great potential for the use of the anti-counterfeiting system.

Bright Nonblinking Photoluminescence with Blinking Lifetime from a Nanocavity-Coupled Quantum Dot.

Colloidal quantum dots (QDs) are excellent luminescent nanomaterials for many optoelectronic applications. However, photoluminescence blinking has limited their practical use. Coupling QDs to plasmonic nanostructures shows potential in suppressing blinking. However, the underlying mechanism remains unclear and debated, hampering the development of bright nonblinking dots. Here, by deterministically coupling a QD to a plasmonic nanocavity, we clarify the mechanism and demonstrate unprecedented single-QD brightness. In particular, we report for the first time that a blinking QD could obtain nonblinking photoluminescence with a blinking lifetime through coupling to the nanocavity. We show that the plasmon-enhanced radiative decay outcompetes the nonradiative Auger process, enabling similar quantum yields for charged and neutral excitons in the same dot. Meanwhile, we demonstrate a record photon detection rate of 17 MHz from a colloidal QD, indicating an experimental photon generation rate of more than 500 MHz. These findings pave the way for ultrabright nonblinking QDs, benefiting diverse QD-based applications.

Manipulations of Electronic and Spin States in Co-Quantum Dot/WS2 Heterostructure on a Metal-Dielectric Composite Substrate by Controlling Interfacial Carriers.

Charge and spin are two intrinsic attributes of carriers governing almost all of the physical processes and operation principles in materials. Here, we demonstrate the manipulation of electronic and spin states in designed Co-quantum dot/WS2 (Co-QDs/WS2) heterostructures by employing a metal-dielectric composite substrate and via scanning tunneling microscope. By repeatedly scanning under a unipolar bias, switching the bias polarity, or applying a pulse through nonmagnetic or magnetic tips, the Co-QDs morphologies exhibit a regular and reproducible transformation between bright and dark dots. First-principles calculations reveal that these tunable characters are attributed to the variation of density of states and the transition of magnetic anisotropy energy induced by carrier accumulation. It also suggests that the metal-dielectric composite substrate is successful in creating the interfacial potential for carrier accumulation and realizes the electrically controllable modulations. These results will promote the exploration of electron-matter interactions in quantum systems and provide an innovative way to facilitate the development of spintronics.

DNA‐Programmed (De)Hybridization of Near‐Infrared Photosensitized UCNP‐QDs‐GNPs Nanoprobes for MicroRNA Imaging and Image‐Guided Cancer Therapy

AbstractAccurate and sensitive analysis of cancer‐associated microRNAs in living tissue is of great significance for the early diagnosis and treatment of cancer. Herein, a hierarchical nanoprobe denoted as UCNP‐QDs‐GNPs is delicately designed, where a near‐infrared (NIR) absorptive upconversion nanoparticle (UCNP) serves as the core, broad‐absorptive and bright emissive quantum dots (QDs) and emission‐quencher gold nanoparticles (GNPs) surround as satellites for microRNA imaging and image‐guided cancer therapy. Through the programmed assembly of heterobivalent DNA‐conjugated QDs with DNA‐modified GNPs and UCNPs, the well‐defined nanostructured UCNP‐QDs‐GNPs are generated with quenched fluorescence. Upon encountering the microRNA‐21 target, GNPs underwent catalytic disassembly, resulting in the concurrent recovery and amplification of fluorescence from QDs and UCNPs, which enabled sensitive imaging and quantification of microRNA‐21 within living cells. Furthermore, dithiol‐constituted aggregation‐induced emission (AIE) photosensitizers bonded on the surface of QDs, are effectively photosensitized by the QDs. The NIR excitation harvested by UCNPs is therefore efficiently transferred to QDs and subsequently converged on the AIE photosensitizers, boosting photodynamic activity for image‐guided therapy in deep‐seated tumors. The DNA‐programmed (de)hybridization strategy, facilitating the conversion of NIR excitation into imaging signals and photodynamic activity, offers a promising avenue for the early theranostics of malignancies.

Bright silicon quantum dot synthesis and LED design: insights into size–ligand–property relationships from slow- and fast-band engineering

Abstract Multicolor, bright silicon quantum dots (SiQDs)—SiQDs with photoluminescence in a range of colors and quantum yields (PLQYs) of >90%—are promising heavy-metal-free light sources for full-color displays, lighting, and biomedical imaging. Colloidal SiQDs can be used to manufacture devices via printing and roll-to-roll processing. Furthermore, the in vivo use of biodegradable SiQDs and Si nanomaterials, for imaging cancer cells and as drug delivery systems, has been demonstrated. However, a large body of research demonstrates that the photoluminescence (PL) wavelength and PLQY of colloidal SiQDs are dependent not only on the SiQD particle size but also on the methods and/or procedures and chemical reagents used to synthesize them. This is because SiQDs are quite sensitive to both the intrinsic properties of Si and external factors. These intrinsic and external factors can be respectively linked to different PL mechanisms: the quantum confinement effect, which produces a slow-decaying “S”-band PL signal, and surface ligand effects, corresponding to fast-decaying “F”-band PL. This review focuses on mechanistic insights into the relationships linking the structures, ligands, and optical properties of SiQDs. Synthesis methods and the application performance of bright multicolor colloidal SiQDs, based on excellent state-of-the-art experimental and theoretical studies, are also reviewed.

Highly bright solid-state carbon dots for efficient anticounterfeiting.

Carbon dots (C-dots) as promising fluorescent materials have attracted much attention because of their low toxicity and excellent optoelectronic properties. However, the aggregation-caused quenching (ACQ) of the solid-state C-dots has limited their potential applications in anti-counterfeiting and optoelectronic devices. In this work, C-dot powder was prepared by directly dispersing the as-prepared C-dots in a polymer matrix or in situ formation of the C-dot/Ca-complex by vacuum heating in the presence of boric acid. The as-prepared C-dots have high quantum yields (QYs) in the range of 40-67% with temperature-dependent photoluminescent (PL) properties. As a proof of concept, the as-synthesized C-dots were used to produce a flexible anti-counterfeiting code and showed high-level security. This highlights the potential of C-dots in solid-state information, anti-information encryption and anti-counterfeiting.

Bright and Stable Yellow Quantum Dot Light-Emitting Diodes Through Core-Shell Nanostructure Engineering.

Solution-processed and efficient yellow quantum dot light-emitting diodes (QLEDs) are considered key optoelectronic devices for lighting, display, and signal indication. However, limited synthesis routes for yellow quantum dots (QDs), combined with inferior stress-relaxation of the core-shell interface, pose challenges to their commercialization. Herein, a nanostructure tailoring strategy for high-quality yellow CdZnSe/ZnSe/ZnS core/shell QDs using a "stepwise high-temperature nucleation-shell growth" method is introduced. The synthesized CdZnSe-based QDs effectively smoothed the release stress of the core-shell interface and revealed a near-unit photoluminescence quantum yield, with nonblinking behavior and matched energy level, which accelerated radiative recombination and charge injection balance for device operation. Consequently, the yellow CdZnSe-based QLEDs exhibited a peak external quantum efficiency of 23.7%, a maximum luminance of 686050cdm-2, and a current efficiency of 103.2cdA-1, along with an operating half-lifetime of 428523h at 100cdm-2. To the best of the knowledge, the luminance and operational stability of the device are found to be the highest values reported for yellow LEDs. Moreover, devices with electroluminescence (EL) peaks at 570-605nm exhibited excellent EQEs, surpassing 20%. The work is expected to significantly push the development of RGBY-based display panels and white LEDs.