Alloyed Quantum Dots Research Articles

Gradient Alloyed Quantum Dots for Photocatalytic Lignin Valorization via Proton Coupled Electron Transfer

In the field of photocatalytic lignin valorization, simultaneously fulfilling the requirements of broad light harvesting and strong redox ability has been a key challenge for single binary quantum dot (QD) photocatalyst systems. In order to address the problem, gradient alloyed QDs with funnel-shaped energy structures have been developed. The gradient energy level increases the photon absorption range, while the periphery energy bands at the funnel edge are sufficiently wide to preserve effective redox capacity. In this work, the gradient alloyed QD photocatalyst along with proton donors have been employed in enhancing the efficiency and selectivity of β-O-4 bond cleavage in lignin, realizing yields of target aromatic products phenol and acetophenone to increase up to 70% and 65%, respectively. The mechanism of conversion from the ketone intermediate to target products and how to choose suitable proton donors have been systematically investigated. We propose a proton-coupled electron transfer (PCET) photocatalytic strategy through producing a Cα radical from ketone with the help of acid possessing appropriate bond dissociation free energy (BDFE) and strong electronic transmission facilitating ability. The knowledge acquired in this work is useful for designing photocatalysts and proton donors that can effectively cleave bonds in lignin via the PCET mechanism.

Observable Hole-State Kinetics and Its Implications for Optical Gain in Hole-Engineered Quantum Dots

Disentangling carrier kinetics is of both fundamental and technological importance for optoelectronics, while the hole-state dynamics in Cd chalcogenide quantum dots (QDs) remains far from understood. Herein, we take the CdZnS-based alloyed QDs as the model system to examine the hole-state dynamics by transient absorption (TA) spectroscopy. The spectroscopic signature of the hole states could be directly manifested from the TA spectra, even in low-quality CdZnS QDs, which arises from the distinctive features of alloyed QDs. By completely passivating the hole traps, the resulting CdZnS/ZnS QDs feature a significant hole contribution of 17% to the TA bleach and associated bleach buildup kinetics. These merits endow the CdZnS-based QDs with excellent optical gain properties, where an ultralong gain lifetime (1.1 ns) and a broad gain bandwidth (>300 meV) have been observed thanks to the positive trion-suppressed Auger recombination and the retarded hot hole cooling under high excitation intensities. Such a slow hot carrier cooling (200 ps) in the alloyed QDs further indicates their potential in other optoelectronic devices, such as the hot carrier solar concentrators. These findings clarify the characters of the valence band hole and offer insights into the manipulation of hole states for optimizing device performances.

An efficient green-emitting quantum dot with near-unity quantum yield and suppressed Auger recombination for high-performance light-emitting diodes

Near 100% photoluminescence quantum yield (PL QY) is the first target for designing luminescent quantum dots (QDs). Here, an alloyed QD with a core/shell structure of Cd0.194Zn0.806Se0.406S0.594/ZnS is synthesized and characterized by the feature of large core size (about 10 nm) and thin shell (around three ZnS monolayers). It exhibits an efficient green emission with the PL QY of 99.8% and ultra-fast radiative transition rate (kr) of 4.16 × 107 s−1. It demonstrates that the excited state will be rapidly decayed to its ground state through a radiative channel and less vulnerable to non-radiative processes. Under a high pump intensity (254.65 μJ cm−2), the Cd0.194Zn0.806Se0.406S0.594/ZnS QD still owns a long biexciton decay lifetime (τxx) of 1.05 ns and high biexciton QYxx of 25.1%, corresponding to a suppressed non-radiative Auger recombination. The Cd0.194Zn0.806Se0.406S0.594/ZnS QD based light-emitting diode exhibits a peak external quantum efficiency of 20.1% and brightness of over 105 cd m−2 at 5.2 V. We believe that the Cd0.194Zn0.806Se0.406S0.594/ZnS QD not only provides a near-unity QY but also ensures its QD based light-emitting diode (QLED) with an excellent performance, which could be an excellent QD material for QLED applications.

Intense blue emission from one-pot synthesized quaternary CsZnxPb1-xBr3 perovskite quantum dots

Suitable ions incorporation into CsPbX3 perovskite nanocrystals can improve the luminescence efficiency, chemical stability, and more importantly modify the emission bands from semiconductor band gap change, for various applications. In this research, high content Zn2+ was introduced into CsPbBr3 quantum dots through a simple one-pot synthesis method. A new intense blue emission centered at 440 nm was observed from heavy Zn alloyed nanocrystals, for increased semiconductor band gap, along with green emission at 510 nm from CsPbBr3 quantum dots, when the ratio of ZnBr2/PbBr2 precursor was larger than unity. The appearance of Zn 3d peaks and the decreasing of bonding energy of Pb 4f peaks from X-ray photoelectron spectroscopy spectra indicated that Zn2+ ions were incorporated into CsPbBr3 quantum dots to form CsZnxPb1-xBr3 alloyed quantum dots. The elements quantitative analysis showed that partial Zn2+ ions in precursors were involved in the synthesis of the quantum dots, and the Zn alloyed perovskite nanocrystals could be described as CsPbBr3, CsZn0.43Pb0.57Br3, CsZn0.54Pb0.46Br3, CsZn0.68Pb0.32Br3 respectively when the ZnBr2/PbBr2 precursor ratios were 0:1, 1:1, 3:1 and 5:1. The X-ray diffraction patterns confirmed that the incorporation of small radius Zn2+ ions into crystals led to crystal shrinkage, instead of crystal phase change. The transmission electron microscope images of the nanocrystals showed cubic geometries and reduced average sizes from 23.3 nm to 17.6 nm with Zn2+ content increase, resulting in the blue shift of emission bands. The energy dispersive spectroscopy elemental mapping of nanocrystals also confirmed the incorporation of Zn2+ ions into the nanocrystals.

Near-infrared photoactive Ag-Zn-Ga-S-Se quantum dots for high-performance quantum dot-sensitized solar cells.

The high light-harvesting ability of quantum dots (QDs) plays an eminent role in the performance of solar cells. In this study, we synthesized Ag-Zn-Ga-S-Se-based alloyed QDs by colloidal hot injection and characterized them. The X-ray photoelectron spectrum analysis confirms the +1, +2, +3, -2, and -2 oxidation states of, respectively, Ag, Zn, Ga, S, and Se in the QDs, and the energy-dispersive X-ray spectrum analysis confirms the 1:1:1:1.5:1.5 stoichiometric ratio of, respectively, Ag, Zn, Ga, S, and Se. These two results indicate the formation of I-II-III-VI3-type alloyed crystals (AgZnGaS1.5Se1.5 nanocrystals). TEM image analysis reveals the QD nature of the synthesized Ag-Zn-Ga-S-Se nanocrystals. The X-ray diffraction pattern confirms the hexagonal structure. Due to the near-infrared light absorption capability, the synthesized QDs were used as the sensitizer to fabricate QDSCs. The fabricated QDSCs were characterized by using electrochemical impedance spectroscopy and photovoltaic performance studies. The fabricated QDSC have superior electrochemical activity with a photoconversion efficiency of 4.91%.

Defect Control via Compositional Engineering of Zn-Cu-In-S Alloyed QDs for Photocatalytic H2O2 Generation and Micropollutant Degradation: Affecting Parameters, Kinetics, and Insightful Mechanism.

Photocatalytic H2O2 production and recalcitrant pollutant degradation are regarded as promising clean technology toward achieving sustainable solar-to-chemical energy conversion. Herein, nonstoichiometric Zn-Cu-In-S (ZCIS) quaternary alloyed quantum dots (QDs) are rationally fabricated via a reflux method toward H2O2 generation and ciprofloxacin degradation under visible light irradiation. The optimum catalyst (ZCIS-2) exhibits a notable H2O2 production of 1685.2 μmole h-1 g-1 (solar-to-chemical conversion efficiency (SCC), 0.19%), which is 5.3 times higher than that of CuInS2 (CIS), and a ciprofloxacin (CIP) degradation efficiency of 96% in 2 h. The observed improvement in activity corresponds to optimized exciton separation/transfer, broad photon absorption, tunable band alignment, and effective adsorption/activation. In addition, oxygen reduction goes through both direct two-electron single-step reduction and single-electron two-step superoxide radical pathways, whereas CIP degradation proceeds via direct •O2- and indirect •OH radical pathways, as confirmed by scavenger experiments. An appropriate amount of defects improves the adsorption/activation of O2 toward H2O2 and active oxygen species generation that facilitates CIP degradation. The effect of operational parameters, such as pH, surrounding environment, presence of ions, sacrificial agent, etc., on both H2O2 formation and CIP removal is vividly studied. Hence, the current study will provide an in-depth insight into O2 photoreduction and micropollutant removal, which encourages further advancement of potent alloyed quantum dot-oriented photocatalytic systems.

Bandgap engineering of CdTe/CdSe rod-shaped core/shell and CdTeSe ellipsoidal alloy quantum dots with tunable and intense emission

In this work, core CdTe, core-shell CdTe/CdSe and alloy CdTeSe QDs are synthesized by aqueous solvent. TEM visually shows the rod-shaped core-shell structure with a transverse to longitudinal ratio of 6.5 and the ellipsoidal alloy structure with different crystal planes competing for growth. The XRD and Raman spectra of the three QDs illustrate the characteristics of the internal lattice structure. With the increase of reaction time, CdTe emission maximum (EM) shows a red shift of 84 nm. Stokes shift changes little, and full width half maximum (FWHM) increases slightly. Compared with the CdTe, the red shift of CdTe/CdSe EM is slowly first and then faster, with a total shift of 125 nm. Stokes shift increases obviously. The initial FWHM is larger than CdTe and the widening speed is gradually accelerated. The initial EM of CdTeSe is red shifted compared with CdTe, and the total red shift of EM is 72 nm. Stokes shift increases obviously. The initial FWHM is significantly wider than CdTe. FWHM first decreases and then increases with reaction time. CdTe shows obvious band edge exciton absorbance of photoluminescence excitation (PLE) spectrum between 356 nm and 400 nm. CdTe/CdSe shows double band edge exciton absorption at 354–373 nm and 401–436 nm due to wave function separated of core-shell structure. The PLE spectrum of CdTeSe shows an obvious upward trend at 306–373 nm due to high energy level nonradiation. The average lifetime of CdTe/CdSe increases by 53 ns compared with CdTe due to the spatially separated electrons and holes. The defect state of CdTeSe increases the proportion of fast delay, which is 2 ns shorter than the average lifetime of CdTe. The transition mechanism of core-shell indirect band gap and alloy direct band gap is explained according to the valence bands of each element shown by XPS and the simulation of energy band density of states. The thickness shell and the doping elements can be adjusted to provide rich variation in the optical properties. This provides a more definite direction for the applications of cadmium chalcogenide in the fields of photoelectric devices and biology. • Type I and type II transformation through Rod-shaped core/shell and ellipsoidal alloy QDs. • Tunable emission achieved by adjusting morphology, lattice structure and valence bond connection. • Precise and rich regulation of band gap engineering. • Providing a more definite direction for the applications of cadmium chalcogenide QDs.

Quaternary alloyed quantum dots with a wide-ranging tunable emission for high color-rendering white light-emitting diodes

Quaternary alloyed quantum dots (QDs) Ag-Zn-In-S(AZIS)/ZnS were prepared by using of heating-up method for the synthesis of AZIS cores followed by a hot-injection method for the shelling of ZnS. By regulating the Ag:Zn:In ratio, the peak emissions of the resulted AZIS/ZnS QDs exhibited an unreported wide ranging tunable emission from 475 nm to 645 nm. With the increasing silver components, redshift in the photoluminescence spectrum was observed. White light-emitting diodes (WLEDs) were fabricated successfully by employing the yellow-green emission AZIS/ZnS QDs and the combination of the green and the red emission ones as color converters respectively. These devices showed satisfied luminescent properties including a highest color-rending index of 88 accompanied by a corelated color temperature of 3260 K. However, AZIS/ZnS QDs integrated on the chips exhibited large redshift compared to their solution states. This redshift was suppressed remarkably by coating the as synthesized AZIS/ZnS QDs with a silica shell using the hydrolysis of tetramethoxysilane (TMOS). The WLEDs based on silica-coated AZIS/ZnS QDs showed an ultrahigh CRI of 96.3 accompanied by a CCT of 3653 K and good resistance to the invasion of room temperature and humidity after placed under room environment for 11 months. Possessing no heavy metal elements and satisfied luminescent properties combined with good resistance to the invasion of room temperature and humidity in devices make AZIS/ZnS QDs be expected to play a critical role in various applications of lighting.

Ternary atoms alloy quantum dot assisted hole transport in thin film polymer solar cells

Quantum confinement effects and multiple exciton generation (MEG) were explored in this investigation to assist the hole transport and improved trapping of light in thin film solar cells (TFOSCs). The popular organic transport material Poly (3,4-ethylene dioxythiophene): polystyrene sulfonate (PEDOT:PSS) is employed here for effective electron blocking and hole transport processes through doping with quantum dots (QD). Alloyed CdTeSe QD is used, at different concentrations, in PEDOT:PSS layer to fabricate TFOSCs in the convectional device structure consisting of molecules blended as poly (3-hexylthiophene): (6, 6)-phenyl- C61-butyric acid methyl ester (P3HT: PCBM) solar absorber. A remarkable increase in performance of the devices was achieved from TFOSC whose HTL doped with QDs that resulted in an optimal boost in power conversion efficiency (PCE) as high as 111.7% relative to the reference cell. The results suggest that the doping of HTL with the alloy of CdTeSe quantum dots assisted in electron blocking, and improved hole collection as well as improved light trapping at the interface between the solar absorber layer and HTL.

Enabling ultranarrow blue emission linewidths in colloidal alloy quantum dots by decreasing the exciton fine structure splitting and exciton-phonon coupling

Enabling ultranarrow blue emission linewidths in colloidal alloy quantum dots by decreasing the exciton fine structure splitting and exciton-phonon coupling

Aggregation-based phase transition tailored heterophase junctions of AgInS2 for boosting photocatalytic H2 evolution

Due to high defect tolerance and multiphase allowance, AgInS2 (AIS) quantum dots (QDs) provide chances for designing new type junctions via tailoring defects, size, or phase structure. These new type junctions potentially enhance photoelectric performance, such as photocatalytic H2 evolution (PHE). Here, ultra-small AIS QDs (∼1 nm) with well-defined exciton absorption were prepared aqueously via a reverse hot-injection procedure for the first time. A coalescence or fast aggregation-based growth was observed for coarsening at 95 or 135 ℃, respectively. XRD and TEM investigations revealed that the tetragonal-orthorhombic (t-o) phase transition occurred via aggregation-based growth. The studies on phase transition kinetics resulted in fine-tailoring on AIS polymorphs, favoring t-o AIS junctions. UV–vis absorption spectra confirm the double absorption edge of the t-o heterophase junction with enhanced visible absorption. Steady and transient PL spectra suggest improvements in carriers’ separation/transfer in this t-o junction. As a result, the optimized t-o AIS shows superior photocatalytic H2 evolution rates of 1022 μmol. g−1. h−1, 51.1 times that of t-AIS or 3.8 times that of o-AIS. This work is expected to provide new insight for designing ternary alloyed QDs with strongly coupled interfaces for effective H2 generations.

Study of surface enhanced fluorescence of CdSeS/ZnS alloyed quantum dots using cytop layer as a dielectric spacer

Recently, the surface enhanced fluorescence technique has been helpful for several biological applications. Some researchers have reported the SEF of fluorophores such as dye molecules and QDs using dielectric spacers formed by several approaches. Herein, for the first time, we report the SEF spectra of CdSeS/ZnS alloyed quantum dots (QDs) that have high photostability, less toxicity, and high biocompatibility. Interestingly, the thin cytop layers formed by a simple approach are used as “dielectric spacers” between Au nanoparticles in the plasmon-active substrate (PAS) and the QDs. For comparison, the spectra of QDs dispersed directly on (i) bare PAS, (ii) bare glass substrate, and (iii) cytop coated glass substrate are also recorded. The enhancement factor is found to vary from one to two orders of magnitude. Since the SEF enhancement depends on the electric field intensity enhancement (EFIE) in the PASs, Finite Element Method (FEM) simulations are performed to estimate the EFIE and its dependence on the thickness of the cytop layer and size of the nanogap between nanoparticles in the PASs.

Photophysics and photovoltaic properties of Zn-alloyed Ag-In-S quantum dots sensitized solar cells

Quantum dots (QDs) have attracted attention for use in photovoltaic applications. However, till now, QDs sensitized liquid junction solar cells (QDSCs) are primary concentrated on binary QDs that contain toxic elements which limit their practical applications in regarding of environmental issues. Hence, the study of less-toxic ternary such as AgInS2 (AIS) and CuInS2 (CIS) or core/shell AIS/ZnS and CIS/ZnS QDs with high power conversion efficiency (PCE) is the most common way for commercial applications. Although significant improvement has been realized for AIS (CIS) QDSCs by overgrowth of wide bandgap ZnS to form quasi type-I core/shell structure for eliminating surface trapping defects where the PCE is comparable or even better than toxic QDs, simultaneously the shell could also cause impeding electron injection from QDs to metal oxide matrix (TiO2) and hole scavenge. For resolving this problem, diffusion of Zn2+ into QDs forming alloyed QDs is a better strategy to improve the conductivity and thus the PCE owing to alloyed QDs could not only reduce the density of trap defects but also regulate the bandgap and contribute to electron injection. Herein, the highly luminescent heavy-metal free and hydrophilic Ag-In-S-Zn alloyed QDs with broad light harvesting range to near infrared (NIR) were synthesized as effective sensitizer for constructing QDSCs, where the optimal PCE of 3.12% was achieved. Moreover, surface passivation by deposition of ZnS layer over the sensitized electrode was also primarily studied to decrease the QDs/electrolyte/TiO2 interface recombination and a champion PCE of 3.78% was obtained.

(Invited, Digital Presentation) Controlling the Energy Structure of Ag(In,Ga)S Quantum Dots for Photocatalytic H2 Evolution

Quantum dots (QDs) composed of group I-III-VI semiconductors, such as CuInS2 and AgInS2, exhibit unique size- and composition-dependent physicochemical properties different from bulk materials due to the quantum size effect. Furthermore, these QDs have attracted intense attention for developing highly efficient solar energy conversion systems, because of the less toxicity and the large absorption coefficients in visible and near-IR regions. Recently we have successfully prepared alloy QDs composed of ZnAgInS or ZnAgInSe semiconductors, the Eg of which was tunable in the visible or near-IR wavelength regions, respectively [1, 2]. Their photocatalytic H2 evolution activity was controlled by the chemical composition and size of QDs. On the other hand, the Eg of bulk I-III-VI semiconductors can be controlled by alloying different metal cations of group III elements. Thus, in this study, we prepare spherical QDs composed of less-toxic AgIn(1-x)GaxS2 (AIGS(x)) alloy semiconductor and report their composition-dependent photocatalytic activity for H2 evolution under visible light irradiation.AIGS(x) QDs with different x values were synthesized by thermal decomposition of Ag(OAc), In(acac)3, Ga(acac)3, and S powders in a mixture solution of oleylamine and dodecanethiol. The chemical composition of resulting QDs, that is, x value, could be controlled by varying the Ga/(In+Ga) ratio in preparation. Thus-obtained AIGS QDs were surface-coated with ZnS shell of various thickness, resulting in the formation of core-shell-structured QDs, AIGS(x)@ZnS. Finally, the ligands modified on the nanocrystal surface were changed from dodecanethiol to mercaptopropionic acid to improve the dispersibility of QDs in an aqueous solution.The obtained AIGS QDs had a spherical shape with size of ca. 4 nm. The ZnS thickness of AIGS(x)@ZnS was varied from 0 to ca. 2 nm. The photocatalytic activity of AIGS(x)@ZnS QDs was investigated for H2 evolution as a model reaction. The irradiation to AIGS(x)@ZnS QDs suspended in an aqueous solution containing Na2S as a hole scavenger was carried out using Xe lamp light (λ> 350 nm). With the elapse of light irradiation, the amount of H2 evolved linearly increased, regardless of the composition of AIGS core or the ZnS shell thickness. The H2 evolution rate was remarkably dependent on the composition of AIGS core: A volcano-type dependence was observed between the H2 evolution rate and the Ga fraction. The highest photocatalytic activity was obtained for AIGS(x)@ZnS QDs with x=0.6 and the ZnS shell thickness of ca. 2 nm. This behavior can be explained by the changes in the stability of AIGS core in aqueous solutions, the conduction band minimum level of QDs, and the amount of photon absorption. References Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, and T. Torimoto, J. Phys. Chem. C, 2015, 119, 24740-24749.P.-Y. Hsieh, T. Kameyama, T. Takiyama, T. Yamamoto, Y.-J. Hsu and T. Torimoto, J. Mater. Chem. A 2020 , 8, 13142-13149.

Controlling the emission linewidths of alloy quantum dots with asymmetric strain

The emission linewidth of quantum dots (QDs) is one of the important optical properties, which is essential for the applications of QD lasers, high-quality displays, and biological imaging. However, we know less about controlling emission linewidth and its underlying mechanisms. Here we introduce a wurtzite ZnSe shell onto a wurtzite CdSe core to produce asymmetric strain due to their large, anisotropic lattice mismatch. Such asymmetric pressure induces significant splitting (ΔAB) between heavy-hole (hh) and light-hole (lh) in valence band (VB). We show that the emission intensity from the lh state (Elh) is significantly suppressed with the increasing ΔAB caused by the strong asymmetric strain. We demonstrate that the exciton-phonon coupling (EPC) is greatly inhibited under the anisotropic lattice strain. The alloying process between the core and shell occurs under the strong lattice strain and raises the longitudinal-optical (LO) phonon energy (ELO). Higher LO phonon energy declines LO phonon occupation numbers (NLO) and synergistically reduces the EPC. The asymmetrically strained alloy QDs ensemble exhibits highly bright emission with ultra-narrow linewidths of 13.8 nm (∼520 nm) and 15.8 nm (∼620 nm). This concept of band structure regulation via asymmetric strain can provide a new platform for high-quality QDs beyond the currently achieved.

Synthesis and Photoluminescence Characterization of 3- MPA Capped CdZnTe Quantum Dots

3-MPA capped CdZnTe alloy quantum dots synthesized using Na2TeO3 as the tellurium source under open atmosphere conditions in aqueous medium. The optical and photoluminescence properties of the CdZnTe quantum dots characterized using UV-Visible absorption and Photoluminescence spectrum. An excitonic peak at 527 nm observed in the absorption spectrum. Tauc relation and Urbach relation were employed to find the bandgap energy and urbach energy of the CdZnTe quantum dot. The quantum dot particle size was estimated using the bandgap energy from Tauc plot employing tight binding approximation, which was 4.75 nm. A high intense emission peak at 567 nm obtained in the photoluminescence spectrum. The emission peaks correspond to yellow fluorescence. The CIE chromaticity diagram gives color coordinate at (0.41,0.56) with a color purity of 92%. The high intense yellow fluorescent CdZnTe quantum can placed as potential candidates for fluorescent probes, biolabeling and cell imaging applications.

Fabrication of a near-infrared fluorescence-emitting SiO2-AuZnFeSeS quantum dots-molecularly imprinted polymer nanocomposite for the ultrasensitive fluorescence detection of levamisole

Levamisole is an anthelminthic drug that is usually used as a cutting agent to lace illicit cocaine samples and has been classified as a dangerous substance. In this work, we report on the fabrication of a novel fluorescence sensor for levamisole using AuZnFeSeS alloyed quantum dots (QDs)-molecularly imprinted polymer (MIP) nanocomposite. Firstly, organic-phased AuZnFeSeS QDs were synthesized via the organometallic hot-injection pyrolysis of metal precursors, surfactants, and organic ligands. Silica (SiO2) was then encapsulated on the QDs surface to render it compact, stable, and biocompatible. Via a free radical polymerization approach, a robust MIP shell templated with levamisole was coated around the SiO2-AuZnFeSeS QDs surface to form a AuZnFeSeS QDs@MIP core/shell nanocomposite. Passivation of the SiO2-AuZnFeSeS QDs core surface with the MIP shell led to radiative exciton recombination process, whereby the QDs fluorescence was enhanced. Interestingly, the SiO2-AuZnFeSeS QDs was characterized by rod-shaped and spherical-shaped particle morphology. Under optimum conditions, the fluorescence of the AuZnFeSeS QDs@MIP nanocomposite was quenched in the presence of levamisole and was selective against other tested drugs. Quantitative detection was achieved in the concentration range of 0.5 – 100 μM with a limit of detection of 0.05 μM (47.4 nM). Validation of the MIP-levamisole affinity was demonstrated by the superior sensitivity of the AuZnFeSeS QDs@MIP over the AuZnFeSeS QDs@NIP (non-templated material). Levamisole was successfully detected in a mixed drug sample containing cocaine with satisfactory analytical recoveries. This work is the first reported use of a cadmium-free quintenary alloyed QDs@MIP nanocomposite fluorescence detection system for levamisole.

Luminescent alloyed quantum dots for turn-off enzyme-based assay.

A new bioanalytical labeling system based on alloyed quantum dots' (QDs) photoluminescence quenching caused by an enzymatic reaction has been developed and tested for the first time. The catalytic role of the enzyme provides high sensitivity and the possibility of varying detecting time to improve assay sensitivity. Alloyed luminescent QDs were chosen in view of their small size (5-7nm) and the high sensitivity of their optical properties to physicochemical interactions. Here, we described the synthesis of alloyed luminescent QDs and demonstrated the possibility of using them as a luminescent turn-off substrate for enzymatic assay. Synthesized alloyed QDs were found to be a sensitive turn-off substrate for glucose oxidase in homogeneous and heterogeneous assay models. CdZnSeS and CdZnSeS/ZnS QDs covered with dihydrolipoic acid and 2-mercaptoethanol were tested. A glucose oxidase limit of detection of 6.6nM for the heterogenous high-throughput model assay was reached.

Design of Distributed Bragg Reflectors for Green Light-Emitting Devices Based on Quantum Dots as Emission Layer

Light-emitting diodes based on quantum dots as an active emission can be considered as a promising next generation for application in displays and lighting. We report a theoretical investigation of green emission at 550 nm of microcavity inorganic–organic light-emitting devices based on Zn (Te, Se) alloy quantum dots as an active layer. Distributed Bragg Reflector (DBR) has been applied as a bottom mirror. The realization of high-quality DBR consisting of both high and low refractive index structures is investigated. The structures applied for high refractive index layers are (ZrO2, SiNx, ZnS), while those applied for low index layers are (Zr, SiO2, CaF2). DBR of ZnS/CaF2 consisting of three pairs with a high refractive index step of (Δn = 0.95) revealed a broad stop bandwidth (178 nm) and achieved a high reflectivity of 0.914.

Solution-processed self-powered near-infrared photodetectors of toxic heavy metal-free AgAuSe colloidal quantum dots

High-performance, solution-processed, self-powered, near-infrared (NIR) photodetectors based on novel AgAuSe alloy quantum dots (QDs) are fabricated for the first time and their photoelectric properties are explored.