Mixture Of Quantum Dots Research Articles

Microwave-Assisted Heating Method toward Multicolor Quantum Dot-Based Phosphors with Much Improved Luminescence.

Solid-state highly photoluminescent quantum dot (QD)-based phosphors attract great scientific interests as color converters because of an increasing demand for white-light-emitting devices. Herein, a microwave-assisted heating method is presented to fabricate multicolor QD-based phosphors within 30 s through microwave-assisted heating of the mixture of QDs and sodium silicate aqueous solution. In the composites, the formed cross-linked networks not only play as a matrix to prevent QD aggregation in solid state but also cause the variation of the refractive index around QDs and the QD surface optimization, which contributes to good stabilities and twice enhancement in photoluminescence quantum yields (69%) compared with the initial QD aqueous solution (33%). Using the QD-based phosphors as color conversion layers, white-light-emitting diodes were realized with controllable color temperature, high color purity, and high color-rendering index (90.3), which show a great potential in display and illumination. Furthermore, the luminescence lifetime of the QD-based phosphors is less than 25 ns. The potential application of the QD-based phosphors in visible light communication was also demonstrated, with the modulation bandwidth achieving 42 MHz.

Multiplexed analysis combining distinctly-sized CdTe-MPA quantum dots and chemometrics for multiple mutually interfering analyte determination

Semiconductor quantum dots (QDs) have demonstrated a great potential as fluorescent probes for heavy metals monitoring. However, their great reactivity, whose tunability could be difficult to attain, could impair selectivity yielding analytical results with poor accuracy. In this work, the combination in the same analysis of multiple QDs, each with a particular ability to interact with the analyte, assured a multi-point detection that was not only exploited for a more precise analyte discrimination but also for the simultaneous discrimination of multiple mutually interfering species, in the same sample. Three different MPA-CdTe QDs (2.5, 3.0 and 3.8nm) with a good size distribution, confirmed by the FWHM values of 48.6, 55.4 and 80.8nm, respectively, were used. Principal component analysis (PCA) and partial least squares regression (PLS) were used for fluorescence data analysis. Mixtures of two MPA-CdTe QDs, emitting at different wavelength namely 549/566, 549/634 and 566/634nm were assayed. The 549/634nm emitting QDs mixture provided the best results for the discrimination of distinct ions on binary and ternary mixtures. The obtained RMSECV and R2CV values for the binary mixture were good, namely, from 0.01 to 0.08mgL−1 and from 0.74 to 0.89, respectively. Regarding the ternary mixture the RMSECV and R2CV values were good for Hg(II) (0.06 and 0.73mgL−1, respectively) and Pb(II) (0.08 and 0.87mg L−1, respectively) and acceptable for Cu(II) (0.02 and 0.51mgL−1, respectively). In conclusion, the obtained results showed that the developed approach is capable of resolve binary and ternary mixtures of Pb (II), Hg (II) and Cu (II), providing accurate information about lead (II) and mercury (II) concentration and signaling the occurrence of Cu (II).

Polymeric nanohybrids containing SiO2 and C70 for initiation of aniline polymerization in the presence of CdSe quantum dots

This study presents the synthesis of complex hybrid materials containing SiO2, polymer and fullerene C70. The surface of SiO2-Br particles was used for the grafting of poly(methyl methacrylate) (PMMA) through ARGET polymerization technique, followed by the grafting of fullerene C70. The GPC analysis showed that even if the molecular weight increases, the hydrodynamic volume determines lower values with higher PD values. Aniline (ANI) polymerization initiation was achieved by the addition of a C70 suspension to the ANI – CdSe quantum dots mixture. The polymerization involves an electron transfer process that takes advantage on the difference between the HOMO-LUMO energy levels of the participating species.

氧化锌量子点和碳量子点及其复合物的制备与发光性能的研究

氧化锌量子点和碳量子点及其复合物的制备与发光性能的研究

Quantum-Dot and Polychalcone Mixed Nanocomposites for Polymer Light-Emitting Diodes

The present work is aimed at improving the efficiency of light-emitting diodes (LEDs) through the amalgamation of polymeric materials and quantum dots (QDs) in nanocomposites. Herein, we report on the polytriphenylamine-based chalcone (PTpC) or polycarbazole-based chalcone- (PCzC-) QDs mixture nanocomposites as emissive layers for polymer LEDs (PLEDs). QDs were evenly dispersed in the polymer matrix and the synthesized PTpC-QDs and PCzC-QDs nanocomposites were able to form smooth thin films. The luminance characteristics of PTpC-QDs and PCzC-QDs nanocomposites were better than those of the pristine QD, PTpC, and PCzC materials, owing to the high charge-carrier transport ability of polymer-QDs nanocomposites. These results indicate that the proposed polymer-QDs nanocomposites could be potential candidates for application in PLEDs.

Chiroptical activity in colloidal quantum dots coated with achiral ligands.

We studied the chiroptical properties of colloidal solution of CdSe and CdSe/ZnS quantum dots (QDs) with a cubic lattice structure which were initially prepared without use of any chiral molecules and coated with achiral ligands. We demonstrate circular dichroism (CD) activity around first and second excitonic transition of these CdSe based nanocrystals. We consider that this chiroptical activity is caused by imbalance in racemic mixtures of QDs between the left and right handed nanoparticles, which appears as a result of the formation of various defects or incorporation of impurities into crystallographic structure during their synthesis. We demonstrate that optical activity of colloidal solution of CdSe QDs with achiral ligands weakly depends on the QDs size and number of ZnS monolayers, but does not depend on the nature of achiral ligands or polarity of the solution.

Micro‐spectrometer based on 64‐pixel high‐sensitivity quantum dot detector array

A high photoexcited carrier multiplication photodetector operating at room temperature is reported. The device is a GaAs n-i-n photodetector with double-barrier AlAs in which a thin quantum well contains a mixture of quantum dot (QD) structures. This special structure makes the proposed photoelectric detector have high sensitivity to light under an operating temperature of 300 k. Its current responsivity can reach about 7 × 1011 A/W with 0.01 picowatts 633 nm light power and −0.5 V bias. The response voltage is 7 mV at an integration time of 80 μs. The voltage responsivity reached about 2.7 × 109 V/W. An embedded micro-spectrometer based on the high-sensitivity features of the photodetector has also been designed. By means of QD fluorescent sample testing and comparison, the proposed spectrometer is found to have higher sensitivity and a shorter integration time than the ‘NOVA’ spectrometer (product model of the spectrometer of ideaoptics, China) based on a backside-illuminated CCD (Hamamatsu, S7031–1006S). The QD spectrometer was mounded in a hyperspectral microscopy imaging system with an optical path switcher. The system has been used to analyse and to make a comparative study of the biological section. This kind of spectrometer with highly sensitive linear QD detectors has good application prospects in the fields of biological science, medical diagnosis and environmental detection.

Synthesis of fluorescent core-shell nanomaterials and strategies to generate white light

In this work, cadmium free core-shell ZnS:X/ZnS (X = Mn, Cu) nanoparticles have been synthesized and used for white light generation. First, the doping concentration of Manganese (Mn) was varied from 1% to 4% to optimize the dopant related emission and its optimal value was found to be 1%. Then, ZnS shell was grown over ZnS:Mn(1%) core to passivate the surface defects. Similarly, the optimal concentration of Copper (Cu) was found to be 0.8% in the range varied from 0.6% to 1.2%. In order to obtain an emission in the whole visible spectrum, dual doping of Mn and Cu was done in the core and the shell, respectively. A solid-solid mixing in different ratios of separately doped quantum dots (QDs) emitting in the blue green and the orange region was performed. Results show that the optimum mixture of QDs excited at 300 nm gives Commission Internationale del'Éclairage color coordinates of (0.35, 0.36), high color rendering index of 88, and correlated color temperature of 4704 K with minimum self-absorption.

In vivo study of immunogenicity and kinetic characteristics of a quantum dot-labelled baculovirus

Nanomaterials conjugated with biomacromolecules, including viruses, have great potential for in vivo applications. Therefore, it is important to evaluate the safety of nanoparticle-conjugated macromolecule biomaterials (Nano-mbio). Although a number of studies have assessed the risks of nanoparticles and macromolecule biomaterials in living bodies, only a few of them investigated Nano-mbios. Here we evaluated the in vivo safety profile of a quantum dot-conjugated baculovirus (Bq), a promising new Nano-mbio, in mice. Each animal was injected twice intraperitoneally with 50 μg virus protein labelled with around 3*10-5nmol conjugated qds. Control animals were injected with PBS, quantum dots, baculovirus, or a mixture of quantum dots and baculovirus. Blood, tissues and body weight were analysed at a series of time points following both the first and the second injections. It turned out that the appearance and behaviour of the mice injected with Bq were similar to those injected with baculovirus alone. However, combination of baculovirus and quantum dot (conjugated or simply mixed) significantly induced stronger adaptive immune responses, and lead to a faster accumulation and longer existence of Cd in the kidneys. Thus, despite the fact that both quantum dot and baculovirus have been claimed to be safe in vivo, applications of Bq in vivo should be cautious. To our knowledge, this is the first study examining the interaction between a nanoparticle-conjugated virus and a living body from a safety perspective, providing a basis for in vivo application of other Nano-mbios.

Influence of CdSe quantum dot on molecular/ionic relaxation phenomenon and change in physical parameters of ferroelectric liquid crystal

Spherical cadmium selenide (CdSe) quantum dots (QDs), capped with octadecylamine, dispersed in ferroelectric liquid crystal (FLC), can remarkably alter the electro-optical (E-O) parameters (material parameters) of the host compound. Here we present an E-O, dielectric, surface anchoring and fluorescence study demonstrating that the physical properties of host FLC strongly depend on the dopant (QD) concentration. The addition of QDs in FLC changes the surface anchoring of FLC molecules, which results the change in E-O parameters of pristine FLC as a function of QDs concentration. The ion–polarisation coupling induces a new temperature-dependent weak ionic relaxation mode (TDWIRM) in FLC–QDs mixture at a certain concentration of QDs. Dipolar coupling between CdSe QDs and FLC molecules readjust the dielectric properties and molecular/ionic relaxation phenomenon in the FLC–QDs mixtures. The fluorescence of FLC–QDs mixtures is probably due to the coupling between the exciton and photon in LC medium, which leads the radiative process. The behaviour of fluorescence property of FLC–QDs mixtures reveals that the concentration of uniform-sized QDs only changes the fluorescence intensity of the FLC–QDs mixtures.

Low-cost and high-color-quality white light emitting diodes based on CdSe/ZnS quantum dots

Low-cost and high-color-quality white light emitting diodes (WLEDs) have been realized based on CdSe/ZnS colloidal quantum dots (QDs). CdSe/ZnS QDs with different diameters and emission wavelengths were used as phosphors and coated on the unpackaged blue InGaN/GaN LED chips, the emission of QDs and the unabsorbed LED light collectively contribute to the white light generation. Drop-coating and layer-by-layer assembly techniques were used to integrate QDs on the LED chips. Comparison of the experimental results, we found layer-by-layer assembly method with larger QDs at the bottom were the suitable method to generate controllable white light emission. Using this easy and low cost method, WLED samples were fabricated using QD mixtures with one (‘single’), or two (‘dual’) emission wavelengths. High-quality warm WLED were obtained with a correlated color temperature of CCT = 3778 K, tristimulus coordinates of (x, y) = (0.36, 0.28) and color rending index of CRI = 80.8.

Ionic Bonding between Artificial Atoms

Conventional solids are prepared from building blocks that are conceptually no larger than a hundred atoms. While van der Waals and dipole-dipole interactions also influence the formation of these materials, stronger interactions, referred to as chemical bonds, play a more decisive role in determining the structures of most solids. Chemical bonds that hold such materials together are said to be ionic, covalent, metallic, dative, or otherwise a combination of these. Solids that utilize semiconductor nanocrystal quantum dots as building units have been demonstrated to exist; however, the interparticle forces in such materials are decidedly not chemical. Here we demonstrate the formation of charge transfer states in a binary quantum dot mixture. Charge is observed to reside in quantum confined states of one of the participating quantum dots. These interactions lead to materials that may be regarded as the nanoscale analog of an ionic solid. The process by which these materials form has interesting parallels to chemical reactions in conventional chemistry.

Quantum Dot Based Sensing Platform for Selective Detection of Volatile Organic Compounds and Biomarkers

Diagnosing and monitoring diseases such as lung cancer often involves expensive testing in advanced stages of development. An inexpensive method is desired for earlier detection and improved prognosis. Such diseases cause changes in body chemistry that result in the release of volatile organic biomarkers (VOBs) that are often different than those of healthy patients. Therefore, appropriate analysis of patients’ breath can lead to early diagnosis and monitoring. The objective of this research is to understand and improve new non-invasive selective sensors to quantify specific VOBs. These sensors consist of mixture of quantum dots and dye. The dye becomes colored when exposed to volatile organic biomarkers without a significant difference in color for different biomarkers. However, when the dye is tethered to quantum dots and exposed to light, the color for each biomarker is quantifiably different. Such a combination creates a sensitive and selective sensor for disease specific VOBs.

Simultaneous measurement of position and color of single fluorescent emitters using diffractive optics

We propose a method for simultaneously measuring the position and emission color of single fluorescent emitters based on the use of a large pitch diffraction grating in the emission light path. The grating produces satellite spots adjacent to the main spot; the relative distance between the spots is a measure for the emission wavelength. We present proof-of-principle experiments on beads and mixtures of quantum dots using a spatial light modulator for making a programmable diffraction grating. A wavelength precision of around 10nm can be achieved for 1000 signal photons and practical background levels, while maintaining a localization precision of around 10nm.

Synthesis of Multifunctional Silica Composites Encapsulating a Mixture Layer of Quantum Dots and Magnetic Nanoparticles

Multifunctional silica colloidal composites with enhanced photoluminescence (PL) and superparamagnetism are reported. Enhanced PL and superparamagnetism were achieved by encapsulating a mixture layer of quantum dots (QDs) and superparamagnetic iron oxide nanoparticles (SPIONs) within a silica sphere, wherein QDs and SPIONs were capped by 3-mercaptopropionic acid (MPA) and 2-carboxy ethyl phosphonic acid (CEPA), respectively. The silica composites encapsulating a mixture layer of QDs and SPIONs, i.e., S(Q,M)S core(layer)shell architectures with various diameters (80, 360, and 900 nm) were successfully prepared by utilizing electrostatic interaction between positively charged amine-functionalized silica (S) and negatively charged mixture of QD–MPA (Q) and SPION–CEPA (M) and then, by forming a silica shell of 10–20 nm. The S(Q,M)S showed more than twice higher PL intensity than MPA-capped QD with the same QD concentration. Increasing the molar ratio of M/Q from 0.02 to 0.05 in the S(Q,M)S increased the saturation magnetization value from 0.15 to 0.62 emu/g. The S(Q,M)S composites with enhanced PL intensity and superparamagnetism are expected to be a plausible probe material for bioimaing and sensing application. Also, the current synthetic strategy for S(Q,M)S composites is expected to be extendible to include other functional nanoparticles.

CMOS BQJ detector chip with integrated charge-amplifiers for fluorescence measurements

A CMOS buried quad-junction (BQJ) photodetector chip was designed for quantitative analysis in multi-labeling fluorescence detection applications. The chip integrates four-channel charge preamplifiers associated to the multi-output BQJ detector. The chip was tested for noise analysis and evaluation of the amplifiers’ characteristics. It has a sensitivity of 21.2V/lxs at 555nm and a detectivity D* up to 3×1013cmHz1/2W−1. A test of the chip for a two-label fluorescence case was performed using a mixture of quantum dots in a priori unknown proportions. Good agreement was obtained between the modeled and measured results.

Efficient hybrid solar cells using PbSxSe1−x quantum dots and nanorods for broad-range photon absorption and well-assembled charge transfer networks

We present hybrid solar cells with high efficiency utilizing a novel donor-acceptor combination of poly[2,6-(4,4'-bis-(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-alt-4,7(2,1,3-benzothiadiazole)] (PSBTBT) and a PbSxSe1-x inorganic semiconductor. Several nanocomposite parameters are evaluated in order to improve the hybrid device efficiency, including donor-acceptor materials, surface modification of the inorganic semiconductor, and mixture of quantum dots (QDs) and nanorods (NRs) in the polymer matrix. A high power conversion efficiency (PCE) of ~3.4% is attained from the optimal device with a PbS0.7Se0.3 QD : NR blending ratio of 0.3 : 0.7 (wt/wt) under air mass (AM) 1.5 solar illumination, which is attributed to the broad-range absorption of the solar energies and the efficient charge separation and transport dynamics. The optoelectronic and nanomorphological properties of these novel hybrid solar cells are described.

Site-Selective Chelation and Excitation Energy Transfer between the Higher Plant Major Light-Harvesting Complexes and Quantum Dots

The major light-harvesting complexes of photosystem II(LHCII) have been linked to many organic or inorganic materials to construct bio-inspired new hybrid materials. In this study, the authors reported a hybrid complex of recombinant LHCII and water-soluble quantum dots(QD) linked by nickel-nitriloacetic acid(NTA·Ni) with a series of molar ratio between LHCII and QD(1∶64, 1∶32, 1∶16, 1∶12, 1∶8, 1∶4,1∶2.7, 1∶2, 1∶1.6) on the QD and histidine tag on the LHCII. The spectroscopic results showed that the fluorescence at 680 nm from LHCII increased when more QD molecules were put into the hybrid system.The enhancement reached the maximum and saturated when the molar ratio between LHCII and QD was2.7∶1. The fluorescence spectra results could be explained by resonance energy transfer mechanism from QD to LHCII. Moreover, no obvious energy transfer was observed between native LHCII and QD mixture and this highlighted the necessity of linkage for such energy transfer.

Novel switchable sensor for phosphate based on the distance-dependant fluorescence coupling of cysteine-capped cadmium sulfide quantum dots and silver nanoparticles

A novel switchable sensor was developed for the determination of phosphate based on Ce(3+) induced aggregation and phosphate triggered disaggregation of cysteine (Cys)-capped CdS quantum dots (QDs) and silver nanoparticles (AgNPs). The rare earth metal Ce(3+) could aggregate a mixture of QDs and AgNPs, which induced electron or energy transfer between CdS QDs and AgNPs and serious fluorescence quenching. However, phosphate dissociated the formed aggregation of CdS QDs and AgNPs, restoring the enhanced fluorescence of Cys-capped CdS triggered by AgNPs. Although, CdS QDs alone could also be used to detect phosphate through the aggregation-disaggregation mechanism adjusted by Ce(3+) and phosphate. It was found that the distance-dependent interaction between AgNPs and CdS QDs driven by Ce(3+) and phosphate could lead to enhanced quenching or enhancement of the fluorescence of Cys-capped CdS to form a more sensitive detection system for phosphate. The developed method was applied in the detection of phosphate in real water samples with acceptable and satisfactory results.

Nanophotonic droplet: a nanometric optical device consisting of size- and number-selective coupled quantum dots

Although recent advances in fabrication technologies have allowed the realization of highly accurate nanometric devices and systems, most approaches still lack uniformity and mass-production capability sufficient for practical use. We have previously demonstrated a novel technique for autonomously coupling heterogeneous quantum dots to induce particular optical responses based on a simple phonon-assisted photocuring method in which a mixture of quantum dots and photocurable polymer is irradiated with light. The cured polymer sequentially encapsulates coupled quantum dots, forming what we call a nanophotonic droplet. Recently, we found that each quantum dot in the mixture is preferably coupled with other quantum dots of similar size due to a size resonance effect of the optical near-field interactions between them. Moreover, every nanophotonic droplet is likely to contain the same number of coupled quantum dots. In this paper, we describe the basic mechanisms of autonomously fabricating nanophotonic droplets, and we examine the size- and number-selectivity of the quantum dots during their coupling process. The results from experiments show the uniformity of the optical properties of mass-produced nanophotonic droplets, revealed by emission from the contained coupled quantum dots, due to the fundamental characteristics of our method.