Luminescent Quantum Dots Research Articles

Direct patterning of colloidal quantum dots with adaptable dual-ligand surface.

Colloidal quantum dots (QDs) stand at the forefront of a variety of photonic applications given their narrow spectral bandwidth and near-unity luminescence efficiency. However, integrating luminescent QD films into photonic devices without compromising their optical or transport characteristics remains challenging. Here we devise a dual-ligand passivation system comprising photocrosslinkable ligands and dispersing ligands to enable QDs to be universally compatible with solution-based patterning techniques. The successful control over the structure of both ligands allows the direct patterning of dual-ligand QDs on various substrates using commercialized photolithography (i-line) or inkjet printing systems at a resolution up to 15,000 pixels per inch without compromising the optical properties of the QDs or the optoelectronic performance of the device. We demonstrate the capabilities of our approach for QD-LED applications. Our approach offers a versatile way of creating various structures of luminescent QDs in a cost-effective and non-destructive manner, and could be implemented in nearly all commercial photonics applications where QDs are used.

Synthesis of luminescent graphene quantum dots from biomass waste materials for energy‐related applications—An overview

AbstractA review of the current developments in the synthesis of graphene fragments of porous carbon material by utilizing green precursors in the form of graphene quantum dots (GQDs) and their applications in energy storage devices such as supercapacitors, batteries, fuel cells, and solar cells is presented in this study. Two different approaches, including top‐down and bottom‐up, are discussed. The experimental approaches include hydrothermal or solvothermal method, microwave‐assisted method, electrochemical oxidation, controllable synthesis, oxidative cleavage, and carbonization from small molecules or polymers. The advantages and disadvantages of the green synthesis of GQDs are discussed. Current challenges and prospective applications of GQDs in energy‐related areas are presented. A brief outlook is provided for addressing the problems for further advancement of GQDs. It is anticipated that the results discussed in this study will lead to a better understanding of GQDs as well as their significant roles in developing innovative strategies and applications.

Mercury (Hg2+) Detection in Aqueous Media, Photocatalyst, and Antibacterial Applications of CdTe/ZnS Quantum Dots.

In the present work, CdTe/ZnS high luminescence quantum dots (QDs) were synthesized by a facile, fast, one-pot, and room temperature photochemical method. Synthesized QDs were characterized by different structural and optical analyses such as X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR), Raman, photoluminescence (PL) and UV-visible (UV-vis) spectroscopies. The results confirmed the successful growth of the ZnS shell and formation of CdTe/ZnS core/shell structure. CdTe/ZnS prepared QDs indicated a PL quantum yield of about 51%. These high luminescence QDs were used for detection of Hg2+ ions in aqueous media, as catalyst for photodegradation of different organic dyes, and as antibacterial material for the inhibition of bacterial growth. PL intensity of the CdTe/ZnS QDs was completely quenched after addition of 1m molar Hg2+in to the media. Photocatalyst activity of CdTe/ZnS QDs was studied by rhodamine b, methylene blue, and methylene orange as organic dyes under both the sun and UV illuminations, and results showed that CdTe/ZnS QDs had the best photocatalyst activity for methylene blue degradation under UV irradiation and radical scavenger results indicated that electrons have a main role in photodegradation of methylene blue dye by CdTe/ZnS QDs under UV illumination. Antibacterial effects of CdTe/ZnS QDs evaluated by Minimum Inhibitory Concentration (MIC), and Minimum Bactericidal Concentration (MBC) methods against two strains of bacteria. The results of the antibacterial test showed that CdTe/ZnS could inhibit bacterial growth in Bacillus cereus (Gram-positive) and Escherichia coli (Gram-negative G) bacteria.

Luminescence encoding of polymer microbeads with organic dyes and semiconductor quantum dots during polymerization

Luminescence-encoded microbeads are important tools for many applications in the life and material sciences that utilize luminescence detection as well as multiplexing and barcoding strategies. The preparation of such beads often involves the staining of premanufactured beads with molecular luminophores using simple swelling procedures or surface functionalization with layer-by-layer (LbL) techniques. Alternatively, these luminophores are sterically incorporated during the polymerization reaction yielding the polymer beads. The favorable optical properties of semiconductor quantum dots (QDs), which present broadly excitable, size-tunable, narrow emission bands and low photobleaching sensitivity, triggered the preparation of beads stained with QDs. However, the colloidal nature and the surface chemistry of these QDs, which largely controls their luminescence properties, introduce new challenges to bead encoding that have been barely systematically assessed. To establish a straightforward approach for the bead encoding with QDs with minimized loss in luminescence, we systematically assessed the incorporation of oleic acid/oleylamine-stabilized CdSe/CdS-core/shell-QDs into 0.5–2.5 µm-sized polystyrene (PS) microspheres by a simple dispersion polymerization synthesis that was first optimized with the organic dye Nile Red. Parameters addressed for the preparation of luminophore-encoded beads include the use of a polymer-compatible ligand such as benzyldimethyloctadecylammonium chloride (OBDAC) for the QDs, and crosslinking to prevent luminophore leakage. The physico-chemical and optical properties of the resulting beads were investigated with electron microscopy, dynamic light scattering, optical spectroscopy, and fluorescence microscopy. Particle size distribution, fluorescence quantum yield of the encapsulated QDs, and QD leaking stability were used as measures for bead quality. The derived optimized bead encoding procedure enables the reproducible preparation of bright PS microbeads encoded with organic dyes as well as with CdSe/CdS-QDs. Although these beads show a reduced photoluminescence quantum yield compared to the initially very strongly luminescent QDs, with values of about 35%, their photoluminescence quantum yield is nevertheless still moderate.

High-Luminescence Electrospun Polymeric Microfibers In Situ Embedded with CdSe Quantum Dots with Excellent Environmental Stability for Heat and Humidity Wearable Sensors.

In this paper, hydrophobic luminescent CdSe quantum dots are successfully dispersed in a mixture of styrene and methyl methacrylate through the oleic to methacrylic acid ligand exchange. Further in situ solution polymerization of the quantum dots in a mixture of styrene and methyl methacrylate followed by electrospinning allowed us to prepare luminescence hybrid styrene-co-methyl methacrylate fibers embedded with quantum dots. CdSe@P(S+MMA) hybrid fibers with 27% quantum yield showed excellent moisture, heat and salt resistance with a photoluminescence output below 120 °C. When dry heated, the hybrid fibers of the fluorescence signals decreased with temperature to 79%, 40%, 28%, 20% and 13% at 120 °C, 140 °C, 160 °C, 180 °C and 200 °C, respectively, due the to the chemical degradation of CdSe QDs. Such hybrid fibers show the potential to manufacture wearable moisture- and heat-sensing protective clothing in a 120–200 °C range due to the thermal-induced quenching of quantum dot photoluminescence.

Nitrogen doped carbon quantum dots (N-CQDs) with high luminescence for sensitive and selective detection of hypochlorite ions by fluorescence quenching

A highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) with a quantum yield of 44% was prepared by a facile hydrothermal synthesis method using citric acid (CA) and ethylenediamine (EDA) with a molar ratio of 1:1 at 200 °C for 5 h. The hypochlorite (ClO−) ions significantly quench the fluorescence of the N-CQDs according to a pseudo-second-order kinetic model. A sensitive and selective quantification method with an excellent linearity in the range of 1.0–10.0 μM was developed to detect ClO− ions based on the fluorescence quenching. The limit of detection (LOD) of 0.43 μM and the limit of quantification (LOQ) of 1.04 μM were achieved, respectively. This approach was successfully applied to detect the residual ClO− ions in local tap water and in swimming pool water. In addition, the developed fluorescence quenching method was also successfully applied in anti-counterfeiting and paper encryption. Both of the applications in real world suggest that the as-prepared N-CQDs is a kind of promising fluorescence probe for rapid detecting ClO− ions in environment fields, and has potential applications in text secrecy fields.

Fast, eco-friendly synthesis of blue luminescent nitrogen-doped graphene quantum dots in glycerol

Nitrogen-functionalized graphene quantum dots (N-GQDs) were synthesized by hydrothermal transformation of glycine precursors in glycerol. Functionalization of GQDs with nitrogen was confirmed with FTIR spectroscopy. Atomic force microscopy (AFM) analysis revealed that the thickness of the quantum dots is around ~ 1 nm while the lateral dimensions are in the range from 20 to 80 nm. N-GQDs exhibit strong fluorescence in the blue (420 nm) region and they are suitable for bioimaging applications.

Luminescent properties of spatially ordered Ge/Si quantum dots epitaxially grown on a pit-patterned “silicon-on-insulator” substrate

The results of studying the luminescent properties of epitaxially grown structures with spatially ordered Ge/Si nanoislands (quantum dots), in which the pit-patterned “silicon-on-insulator” substrates serve both for the spatial ordering of quantum dots and for the two-dimensional photonic crystal formation, are presented. It is found that with a certain choice of pit-patterned substrate parameters (diameter of pits and their spatial period), in the photoluminescence spectra of such structures, the multiple narrow peaks are observed. In addition, a significant increase in the quantum dot luminescence signal intensity occurs in the near-infrared range. The effects are related to resonance interaction of quantum dot emitters with photonic crystal modes. The luminescence enhancement effect persists up to room temperatures.

Full wafer property control of local droplet etched GaAs quantum dots

We present strategies for controlling growth parameters of local droplet etched GaAs quantum dots. We manage the local QD density and emission wavelength by gradient material deposition. We find regions with no light-emitting quantum dots sharply separated from regions with strong quantum dot luminescence. Close to this transition, we expect the lowest quantum dot densities possible under the used parameters. The maximum wavelength shift achieved due to a variation of GaAs hole filling level on a single 3-inch wafer ranges from 731to 795 nm. By locally controlling the surface roughness, a profound additional influence on the emission wavelength and density is found. We show how to control this modulation on a millimeter-scale over the whole wafer.

Plasmon-exciton nanostructures, based on CdS quantum dots with exciton and trap state luminescence

The study is devoted to the establishment of plexciton coupling manifestations in the luminescence of colloidal CdS quantum dots (3.7 nm), passivated with Oleic acid (OA) in mixtures with spherical silver nanoparticles (Ag NPs), coated with Oleylamine (OAm) with size of 10–15 nm. Mixtures of CdS QDs and Ag NPs in toluene, in which the associates formation occurs as a result of the π-staking and dipole-dipole interaction have been realized. The case of the simultaneous effect of plasmonic nanoparticles on exciton and trap state luminescence is considered. Under conditions of maximum overlap of Ag NPs extinction spectrum (415 nm) and exciton luminescence band, it was found that the exciton luminescence quenching (430 nm), accompanied by an decrease in its lifetime from 7.4 ns to 2.5 nm due to resonance energy transfer with an efficiency of 0.66 is dominant effect. At the same time, under conditions of weak plexciton coupling, caused by an insignificant overlap of Ag NPs plasmon band, an increase in the intensity of trap state luminescence (603 nm) by a factor of 1.8 with simultaneous decrease in its luminescence lifetime from 75 ns to 25 ns was observed due to the manifestation of the Purcell effect. The obtained results demonstrate the possibility of increasing the quantum yield of QDs trap state luminescence due to the Purcell effect.

Rapid and green synthesis of highly luminescent MoS2 quantum dots via microwave exfoliation of MoS2 powder and its application as a fluorescence probe for cortisol detection in human saliva

We have introduced a simple, straightforward, green, and fast microwave exfoliation of MoS2 powder to prepare highly luminescent MoS2 quantum dots (QDs). The microwave irradiation of MoS2 powder was evaluated in the different solvents, including EtOH 30%, MeOH 30%, NaOH 1 M, and NH4OH 1 M in both open and closed microwave system setups. The results indicated that the highest luminescent MoS2 QDs is obtained when MoS2 powder was dispersed in 1 M ammonium solution and exposed to 850 W microwave radiation in a closed microwave system at 30 bars for 30 min. Different microscopic and spectroscopic techniques were used to characterize as-prepared MoS2 QDs. The MoS2 QDs have shown the maximum emission at 413 nm with excitation at 310 nm. The Quantum yield of as-prepared QDs was 1.98%. Cu2+, Pb2+, Cd2+, Ag+, Fe3+, and Al3+ quenched the luminescence intensity of MoS2 QDs. The luminescence of MoS2 QDs-Ag+ and Cu2+ mixtures were recovered on addition of cortisol with the higher emission recovery for Cu2+ ion. Therefore, proof-of-concept for cortisol sensing in human saliva was evaluated and discussed using off-on protocol. A linear cortisol calibration curve was obtained in the range of 100 ng mL−1 to 500 ng mL−1, with a detection limit of 16 ng mL−1 (S / N = 3). The method was successful in determining the cortisol content of saliva.

Quantum dot bead-based competitive immunochromatographic assay for enterotoxin aureus A detection in pasteurized milk

Staphylococcal enterotoxin A (SEA) is an important biotoxin, produced by Staphylococcus aureus under appropriate conditions, and often contaminates milk and dairy products. Herein, an anti-SEA monoclonal antibody (anti-SEA mAb) was prepared by injecting the SEA protein in BALB/c mice, and a novel immunochromatographic assay (ICA) was developed for the rapid and sensitive determination of SEA in pasteurized milk by using highly luminescent quantum dot beads (QB) as signal amplification probe. Given the 1020-fold enhancement in the photoluminescence intensity of QB to the original quantum dot, the proposed QB-ICA exhibits high sensitivity for SEA determination in real milk samples with a limit of detection of 1.89 ng/mL, and shows good dynamic linearity for SEA quantitative detection from 2 to 150 ng/mL within 15 min of test time. The proposed QB-ICA also shows good selectivity to SEA detection with a negligible cross-reaction to common analogs, including staphylococcal enterotoxins B, C, D, and E. In addition, the accuracy and precision of QB-ICA were assessed by analyzing SEA-fortified milk samples. The average recoveries of intra- and interassays range from 85.5 to 128.1%, and the coefficients of variation range from 4.6 to 14.2%, indicating an acceptable accuracy for the quantitative detection of SEA in real milk samples. In summary, this work provides a powerful and rapid analysis tool for the sensitive monitoring of SEA contamination in pasteurized milk samples.

High luminescence of CdTe/CdSe/CdS core/shell/shell QDs: synthesis via a simple photochemical approach and gamma dosimetry application

In this research CdTe/CdSe/CdS core/shell/shell quantum dots (QDs) were synthesized by a photochemical approach using thioglycolic acid as capping agent and S2- source for CdS shell growth. X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR), and Raman results confirmed formation of CdTe/CdSe/CdS core/shell/shell structure. Photoluminescence (PL) quantum yield (QY) of the CdTe QDs was 23% and 50 and 70% for CdTe/CdSe and CdTe/CdSe/CdS QDs, respectively. Effect of 60Co gamma irradiation on optical and structural properties of CdTe and CdTe/CdSe/CdS core/shell/shell QDs was investigated. The obtained results indicated stability of crystalline structure of QDs after gamma irradiation but PL intensity of the CdTe/CdSe/CdS QDs decreased gradually after receiving different doses of gamma irradiation with a red shift in PL peak position. The obtained results suggested these luminescence QDs as potential materials for gamma dosimetry.

In-situ synthesis of luminescent CdS quantum dots embedded in phosphate glass

CdS quantum dots (QDs) are a promising nanomaterial for optical and emitter devices. The main difficulty is controlling the QDs growth due to their instability and tendency to agglomerate. Phosphate glasses are an interesting host for QDs owing to their intrinsic characteristics. In this sense, we report an in-situ synthesis of luminescent CdS QDs into a phosphate glass and their growth upon heat treatments (HT) above Tg for different times. Quasi-spherical QDs were obtained with the average size of 8.1 nm and an intense emission at 550 nm under excitation at 340 nm. A significant emission intensity decreases and about 10 nm Stokes shift was observed after HT. Hence, this study describes a facile synthesis of luminescent CdS QDs in a novel and stable glass system, which makes it a promising material for photonic applications with possibility to adjust the emitted light wavelength.

Chemical Fabrication of Efficient Blue‐luminescent Carbon Quantum Dots from Coal Washery Rejects (Waste) for Detection of Hg2+ and Cr6+ Ions in Water

AbstractAn economical facile method was established for the preparation of luminescent carbon quantum dots (CQDs) by utilizing the waste coal washery rejects as precursor materials. The derived CQDs were extensively characterized for their physio‐chemical properties and they (Mcqds and Dcqds) show an efficient maximum quantum yield of 11 % with an average particle size of 2.5‐3.0 nm. The derived CQDs exhibited better physical and chemical properties at maximum excitation and emission wavelengths of 360 nm and 450 nm, respectively, with blue‐light emission. The as‐synthesized CQDs (Mcqds) were applied as a fluorescent sensing probe for sensitive detection of Hg2+ and Cr6+ ions in water samples, showing reasonable limit of detection and quantification with recovery percentage of 96–100 %. The study has shown potential for using such cheap waste‐material derived CQDs as for further development of sensing devices in future.

Highly luminescent pH-responsive carbon quantum dots for cell imaging

Carbon quantum dots (CDs) have attracted tremendous interest owing to their idiosyncratic functions and wide-ranging applications. However, it remains a great challenge to empolder an integrated CDs combining high luminescence, biocompatibility and luminescence color tunability for bioimaging via simple approach. In this work, pH-responsive carbon quantum dots (Si-CDs) with high luminescence (quantum yield = 74.8%) were fabricated by one-step hydrothermal method using (3-mercaptopropyl) triethoxysilane (KH-580) as modifier for the first time. The optical properties of the as-prepared Si-CDs can be controlled from obvious green–blue–violet transformation by altering the pH. More importantly, the change is reversible and repeatable. In addition, the Si-CDs have good biocompatibility and chemically inert in vitro cell system simulation. Such non-toxic, environmental friendly, low-cost, inert CDs materials are promising candidates for biomedical and pH-sensitive sensors.

Multi-layer programmable spectral anti-counterfeiting based on quantum dots inkjet printing.

High security and convenient operation have been the aim of the anticounterfeiting field. An anticounterfeit system in which multiple information are written on an overlapping area with quantum dot (QD) inks of different fluorescence wavelengths that combines spectroscopy technology for information identification is proposed in this study. Because the emission spectra of QDs can be tuned by simply changing the size, ultraviolet (UV) glue mixed with different sizes of CdSe/ZnS QDs is used as the printing ink with different fluorescence wavelengths. Software-design labels with different information are printed on the overlapping area using inks with different luminescent QDs. The printed information can only be identified by the bandpass filter with the corresponding wavelength under UV light. Under natural light, the information cannot be identified by the naked eye. In the proposed anticounterfeiting system, the excitation light and filter are both indispensables. Our method makes the fabrication of anticounterfeit labels flexible in design, fast in production, and high in information concealment. Meanwhile, the proposed system is quick and convenient, which has huge application potential in the field of display and anticounterfeiting.

New-Generation Low-Toxic I–III–VI2 Quantum Dots in Chemical Analysis

Luminescent quantum dots (QDs) of I–III–VI2 semiconductors present a new class of luminescence materials that combine unique optical and electronic properties while exhibiting low toxicity compared to conventional cadmium-based QDs. Advances in the colloidal synthesis of ternary QDs have been used to develop fluorescence chemical and biological sensors for the detection of various analytes. The review covers the main approaches to synthesizing QDs of the I–III–VI2 structure, the features of their structure and properties, and current trends in their use as low-toxic luminescent labels in biomedicine and chemical analysis.

SYNTHESIS OF CdTe QUANTUM DOTS IN AQUEOUS PHASE USING MERCAPTOSUCCINIC ACID

Highly luminescent CdTe quantum dots (QDs) are the most widely used nanoparticles for making fluorescent biosensors and optoelectronic devices. In this paper, we present the successful synthesis of CdTe QDs in the aqueous phase using mercaptosuccinic acid (MSA) as a capping ligand. The CdTe QDs were formed by the reaction of the Te precursor (in TeO2) with Cd2+/MSA in solution at 80 oC for 30 min, then annealing in an autoclave at different temperatures (110 - 150 oC) and time intervals (60 - 180 min). The synthesis of QDs in water has many advantages such as the simplicity, environmental friendliness, and using cheap chemical agents, and particularly make the CdTe QDs suitabble for bioapplications because of the biocompatibility. The high quality of the synthesized CdTe QDs was confirmed by X-ray diffraction (XRD) and their optical properties. The XRD pattern shows the cubic zinc blende structure of the synthesized CdTe QDs. Additionally, the influences of the synthesis parameters, namely the annealed temperature, time to the optical properties of the obtained QDs were systematically investigated with regard to the growth rate and particle size. As a result, CdTe QDs become bigger causing the red-shifted of peaks in their absorption and photoluminescence spectra with increasing annealed temperature and time. This provides evidence for the quantum confinement effect.

Vibronic fingerprints in the luminescence of graphene quantum dots at cryogenic temperature.

Atomically precise graphene quantum dots synthesized by bottom-up chemistry are promising versatile single emitters with potential applications for quantum photonic technologies. Toward a better understanding and control of graphene quantum dot (GQD) optical properties, we report on single-molecule spectroscopy at cryogenic temperature. We investigate the effect of temperature on the GQDs' spectral linewidth and vibronic replica, which we interpret building on density functional theory calculations. Finally, we highlight that the vibronic signatures are specific to the GQD geometry and can be used as a fingerprint for identification purposes.