Ternary Quantum Dots Research Articles

Ag- and Mn-doped ZnInS/ZnS dual-emission quantum dots with zone tunability in the color coordinate

In this work, we used Ag- and Mn-doped ZnInS/ZnS quantum dots (QDs) acting as a new generation of nontoxic dual-emission QDs with simultaneous tunable emission wavelengths and dual-emission ratiometric, which makes nontoxic dual-emission QDs with broad zone tunability in the color coordinate. The Ag-doped ZnInS ternary QDs can give rise to largely tunable emission wavelengths from 497 nm to 631 nm. The ratiometric of Ag and Mn dual emissions can be tuned by controlling Ag–Mn and Mn–Mn dopant coupling. With increased Mn doping amount, the increased Ag–Mn dopant coupling leads to increased Mn emission at the expense of lowered Ag emission and Ag fluorescence lifetime. The Mn–Mn coupling can be controlled by using different doping manners: co-doping Ag and Mn in ZnInS core or separate-doping Ag in ZnInS core and Mn in ZnS shell. Compared with co-doping, separate doping has weaker Mn–Mn interactions, an increased Mn irradiative recombination rate constant, and bright Mn photoluminescence.

Fluorescence properties of alloyed ZnSeS quantum dots overcoated with ZnTe and ZnTe/ZnS shells

Fluorescent alloyed ternary ZnSeS quantum dots (QDs) have been synthesized via the pyrolysis of organometallic precursors. The effects of passivation of ZnTe and ZnTe/ZnS shells on the optical properties of the ternary alloyed ZnSeS core have been studied. A ligand exchange reaction using l-cysteine as a capping ligand was used to obtain water-soluble nanocrystals. The nanocrystals were each characterized by UV/vis absorption and fluorescence spectroscopy, transmission electron microscopy, X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The photoluminescence (PL) quantum yield (QY) of alloyed ZnSeS QDs was 14% and this value increased to 27% when ZnTe was overcoated around the surface but further coating with a ZnS shell decreased the PL QY slightly to 24%. This implies that ZnTe shell suppressed non-radiative recombination exciton states in the alloyed core while further layering with a ZnS shell offered no further improvement in suppressing the defect states. XPS analysis confirmed the presence of the first shell layering but showed a weakened intensity signal of S (2p) and Se (3d) for the ZnSeS/ZnTe/ZnS QDs. Our work demonstrates for the first time that shell passivation of alloyed Zn-based QDs can offer improved optical properties. We hope the optical information presented in this work will be useful in the selection of alloyed Zn-based QDs appropriate for the intended application.

Two blinking mechanisms in highly confined AgInS2 and AgInS2/ZnS quantum dots evaluated by single particle spectroscopy.

Ternary AgInS2 quantum dots (QDs) have been found as promising cadmium-free, red-shifted, and tunable luminescent bio-probes with efficient Stokes and anti-Stokes excitations and luminescence lifetimes (ca. 100 ns) convenient for time resolved techniques like fluorescence life-time imaging. Although the spectral properties of the AgInS2 QDs are encouraging, the complex recombination kinetics in the QDs being still far from understood, limits their full utility. In this paper we report on a model describing the recombination pathways responsible for large deviations from the first-order decay law observed commonly in the ternary chalcogenides. The presented results were evaluated by means of individual AgInS2 QD spectroscopy aided by first principles calculations including the electronic structure and structural reconstruction of the QDs. Special attention was devoted to study the impact of the surface charge state on the excited state relaxation and effect of its passivation by Zn(2+) ion alloying. Two different blinking mechanisms related to defect-assisted charge imbalance in the QD responsible for fast non-radiative relaxation of the excited states as well as surface recharging of the QD were found as the major causes of deviations from the first-order decay law. Careful optimization of the AgInS2 QDs would help to fabricate new red-shifted and tunable fluorescent bio-probes characterized by low-toxicity, high quantum yield, long luminescence lifetime, and time stability, leading to many novel in vitro and in vivo applications based on fluorescence lifetime imaging (FLIM) and time-gated detection.

Facile synthesis of homogeneous CuInS2 quantum dots with tunable near-infrared emission

Ternary CuInS2 quantum dots (QDs) with homogeneous and tunable emission ranging from 693 to 835 nm were synthesized via a one-pot thermolysis route. The fluorescence of CuInS2 QDs was greatly enhanced via surface passivation of ZnS layers.

Tuning the energy band gap of ternary alloyed Cd1-xPbxS quantum dots for photovoltaic applications

Tuning the energy band gap of ternary alloyed Cd1-xPbxS (x: 0, 0.33, 0.5, 0.67 and 1) quantum dots (QDs) for photovoltaic applications is studied. Alloyed Cd1-xPbxS QDs were adsorbed onto TiO2 nanoparticles (NPs) using ssuccessive ionic layer adsorption and reaction (SILAR) methode. EDX measurements ensure the success adsorption of alloyed Cd1-xPbxS QDs onto the TiO2 electrode. At 100 mW/cm2 (AM 1.5) sun illumination, the photovoltaic performance of alloyed Cd1-xPbxS QDs sensitized solar cells (QDSSCs) was measured. The maximum values of Jsc (1.92 mA/cm2) and η (0.36%) for the alloyed Cd1-xPbxS QDSSCs were obtained when the molar ratio of Cd/Pb is 0.33/0.67. the open circuit voltage (Voc) is equal 0.61 ± 0.01 V for all alloyed Cd1-xPbxS QDSSCs. The electron back recombination rates decrease considerably for alloyed Cd1-xPbxS QDSSCs as x value increases, peaking at 0.67. The electron lifetime (τ) for Cd0.33Pb0.67S QDSSCs is one order of magnitude larger than that of the other alloyed Cd1-xPbxS QDSSCs with different x value. Under ON–OFF cycles to solar illumination, the open circuit voltage decay measurements show the high sensitivity and reproducibility of alloyed Cd1-xPbxS QDSSCs.

Preparation and Photovoltaic Properties of Ternary AgBiS2 Quantum Dots Sensitized TiO2 Nanorods Photoanodes by Electrochemical Atomic Layer Deposition

Ternary AgBiS2 quantum dots (QDs) were assembled onto TiO2 nanorods (NRs) film for QD-sensitized solar cell (QDSSC) application by a simple electrochemical atomic layer deposition method (ECALD). Various kinds of methods such as XRD, SEM, EDX and TEM were employed to characterize the structure and morphology of the deposits. The results indicate that stoichiometric AgBiS2 QDs of cubic structure were synthesized and homogeneously anchored on the TiO2 NRs. Furthermore, the optical absorbance of AgBiS2 sensitized TiO2 NRs was greatly enhanced in visible region compared to that of bare TiO2. The QDSSCs based on the AgBiS2 sensitized TiO2 NRs photoanodes were constructed and a maximum photoconversion efficiency of 0.95% with a short-circuit current density of 4.22 mA/cm2, an open-circuit voltage of 0.53 V and a fill factor of 0.43, has been achieved. The inspiring parameters demonstrate that AgBiS2 QDs can be a prospective light absorber in solar cells.

Photoelectrochemical performance of ZnCdSe-sensitized WO3 thin films

Due to its wide gap, WO3 mostly absorbs only the ultraviolet radiation, resulting into lower charge collection and thus necessitating the coupling (doping or sensitization) of WO3 with low band gap materials so as to achieve the photoexcitation and charge separation. This study reports the sensitization of WO3 films with ternary quantum dots (ZnCdSe) using SILAR technique for the first time. The porous WO3 layer was spray deposited using ammonium metatungstate as precursor. The structural, surface morphological and optical properties of the sensitized WO3 thin films were studied. Photoelectrochemical (PEC) studies of the sensitized films showed superior performance to that of unmodified WO3 films. Photocurrent density of 8.53mA/cm2 (at 0V vs Ag/AgCl) was observed for film sensitized with 9 cycles of SILAR deposition annealed at 400°C under nitrogen atmosphere, which is a 120-fold and 14-fold increase in photocurrent density when compared to unsensitized WO3 film and WO3/TiO2 film, respectively. Sensitization with ternary quantum dots as ZnCdSe thus offers two advantages: (i) the lower band gap of ZnCdSe allows it to absorb more energy and in turn produce more charge carriers and (ii) the conduction band of ZnCdSe, which lies above the conduction band of TiO2, results in a better charge transfer from sensitizer to the substrate material.

ZnCdSe-Sensitized WO3 and TiO2 based Photoelectrodes: A Comparative Study

This study compares the characteristics of photoelectrodes obtained by sensitization of two different oxide semiconductors (TiO2 and WO3) with same ternary quantum dots for the first time. TiO2 nanotube arrays were obtained using electrochemical anodization technique while the porous WO3 thin film was spray deposited onto SnO2:F substrate. The ZnCdSe quantum dots were tethered to the oxide substrates employing successive ionic layer adsorption and reaction technique. The influence of the number of deposition cycles on photoelectrochemical properties of sensitized oxide films was investigated. The results obtained show that ZnCdSe sensitized TiO2 nanotube array based photoelectrodes exhibit superior performance compared to ZnCdSe sensitized WO3 films under similar conditions.

Spectroscopic investigation of alloyed quantum dot-based FRET to cresyl violet dye.

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R0, intermolecular distance (r), rate of energy transfer k(T)(r), and transfer efficiency (E) are determined by employing both steady-state and time-resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern-Volmer (K(D)) and bimolecular quenching constants (k(q)) are determined from the Stern-Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD.

Photoelectric performance of TiO2 nanotube array photoelectrodes sensitized with CdS0.54Se0.46 quantum dots

The photoelectrochemical performance of CdSSe quantum dots tethered to a framework of vertically oriented titania (TiO2) nanotubes was studied. The TiO2/CdSSe framework demonstrated improved charge transfer due to its unique band edge structure, thus validating the higher photocurrent generation. The composite film led to an 11-fold enhancement in comparison to the control TiO2 film, implying that the ternary quantum dots and the nanotubular structure of TiO2 work in tandem to promote charge separation and favorably impact photoelectrochemical performance. Further, the results also suggest that structural and optoelectronic properties of TiO2 films are significantly affected by the thicknesses of the CdSSe layer.

Colloidal CuInS2 Quantum Dots as Inorganic Hole-Transporting Material in Perovskite Solar Cells.

To develop novel hole-transporting materials (HTMs) is an important issue of perovskite solar cells (PSCs), especially favoring the stability improvement and the cost reduction. Herein, we use ternary quantum dots (QDs) as HTM in mesoporous TiO2/CH3NH3PbI3/HTM/Au solar cell, and modify the surface of CuInS2 QDs by cation exchange to improve the carrier transport. The device efficiency using CuInS2 QDs with a ZnS shell layer as HTM is 8.38% under AM 1.5, 100 mW cm(-2). The electrochemical impedance spectroscopy suggested that the significantly enhanced performance is mainly attributed to the reduced charge recombination between TiO2 and HTM. It paves a new pathway for the future development of cheap inorganic HTMs for the high efficiency PSCs.

Mechanism to Detect Pesticide Residues in Tealeaves Based on CdZnSe/ZnS Ternary Alloy Quantum Dots

In this report, we present the optical properties of the biosensors fabricated from CdZnSe/ZnS quantum dots. The optical properties such as absorption and emission of the ternary quantum dots before and after coupling with the protein molecules like streptavidine (SA) and acetylcholinesterase enzymes (AChE), to form a biosensor structure, will be presented. In particular, the changes in luminescence intensity according to the pH value of the solution environment containing biosensor have been considered, before and after the presence of pesticides. The changes in luminescence intensity of the biosensor after the presence of pesticide over time from 2 seconds to 26 minutes were also surveyed. We have been carried out the tests to determine the trace amounts of commercial pesticides like Motox 5EC, containing 5% cypermethrin and Tungatin 10 EC, containing 10% abamectin, on the real samples of tealeaves. Some characteristics of the relationship between composition, structure, and special optical properties of ternary alloy quantum dots will also be presented. These studies open up the potential applications of ternary quantum dots for agricultural production.

White light emitting ternary quantum dots phosphors with controllable chromaticity and fluorescence resonance energy transfer

A facile route to produce ternary single nanophosphors with white light is reported. This phosphor combines emission from CdS quantum dots in blue with organic dyes calcein in green and rhodamine B in orange. The chromaticity can be tailored precisely by adjusting the molar ratio of quantum dots to dyes. The phosphors are able to generate a pure white light with CIE coordinate of (x=0.33, y=0.34). The distribution of direct excitation and fluorescence resonance energy transfer (FRET) are inspected by time-resolved photoluminescence decays. The results indicate that direct excitation plays a more important role.

Study on the fabrication of CdZnSe/ZnSeS ternary alloy quantum dots

In an effort to search for new compositions and structures of quantum dots with suppressed blinking photoluminescence (random switching between states of high (on) and low (off) emissivity under continuous photo-excitation) and to serve application purposes in biosensors and in optoelectronic devices, we have studied the fabrication of new CdZnSe/ZnSeS ternary alloy quantum dots (QD). In this work, we present new results on the fabrication of the alloy core/shell quantum dots having a shell thickness of about 1.52 nm and a varied shell composition in Se/S ratio. The influence of the growth temperature on the structural properties (crystalline phase and cell), size and elemental compositions of the core and core/shell QDs is presented. Analysis and in-depth comparison of the calculated ternary QDs' composition are performed based on the energy dispersive X-ray spectroscopy (EDS) data and the first exciton absorption peak position and size. Interpretation of the experimental results is also provided.

Photocarrier recombination dynamics in ternary chalcogenide CuInS2 quantum dots.

Photocarrier recombination dynamics in ternary chalcogenide CuInS2 quantum dots (CIS QDs) was studied by means of femtosecond transient-absorption (TA) and nanosecond time-resolved photoluminescence (PL) spectroscopy. Under strong excitation, the TA dynamics in CIS QDs is well described by a simple rate equation including single-carrier trapping, free-to-bound recombination, and trap-assisted Auger recombination. Under weak excitation, on the other hand, the PL decays of the QDs are composed of a short-lived component caused by surface trapping and a long-lived one caused by free-to-bound recombination. It is found that the surface trapping accelerates markedly with decreasing QD size while the free-to-bound radiative recombination hardly depends on the QD size. Besides this, we observed both a decrease in the PL lifetimes and a dynamic spectral redshift, which are attributed to the surface trapping and the coexistent inhomogeneous broadening in CIS QDs. The spectral redshift becomes less pronounced in CIS/ZnS core/shell QDs because of the suppression of the fast nonradiative recombination caused by the passivation of the surface traps. These results give clear evidence that the free-to-bound model is appropriate for interpreting the optical properties of CIS QDs.

Mercaptophosphonic acids as efficient linkers in quantum dot sensitized solar cells

New mercaptophosphonic linkers are presented for the attachment of ternary quantum dots to ZnO and TiO2 for photovoltaic applications.

DNA‐Programmed Dynamic Assembly of Quantum Dots for Molecular Computation

AbstractDespite the widespread use of quantum dots (QDs) for biosensing and bioimaging, QD‐based bio‐interfaceable and reconfigurable molecular computing systems have not yet been realized. DNA‐programmed dynamic assembly of multi‐color QDs is presented for the construction of a new class of fluorescence resonance energy transfer (FRET)‐based QD computing systems. A complete set of seven elementary logic gates (OR, AND, NOR, NAND, INH, XOR, XNOR) are realized using a series of binary and ternary QD complexes operated by strand displacement reactions. The integration of different logic gates into a half‐adder circuit for molecular computation is also demonstrated. This strategy is quite versatile and straightforward for logical operations and would pave the way for QD‐biocomputing‐based intelligent molecular diagnostics.

DNA-programmed dynamic assembly of quantum dots for molecular computation.

Despite the widespread use of quantum dots (QDs) for biosensing and bioimaging, QD-based bio-interfaceable and reconfigurable molecular computing systems have not yet been realized. DNA-programmed dynamic assembly of multi-color QDs is presented for the construction of a new class of fluorescence resonance energy transfer (FRET)-based QD computing systems. A complete set of seven elementary logic gates (OR, AND, NOR, NAND, INH, XOR, XNOR) are realized using a series of binary and ternary QD complexes operated by strand displacement reactions. The integration of different logic gates into a half-adder circuit for molecular computation is also demonstrated. This strategy is quite versatile and straightforward for logical operations and would pave the way for QD-biocomputing-based intelligent molecular diagnostics.

Cu−In−Ga−S quantum dot composition-dependent device performance of electrically driven light-emitting diodes

Colloidal synthesis of ternary and quaternary quantum dots (QDs) of In/Ga ratio-varied Cu−In1−x−Gax−S (CIGS) with nominal x = 0, 0.5, 0.7, and 1 and their application for the fabrication of quantum dot-light-emitting diodes (QLEDs) are reported. Four QLEDs having CIGS QDs with different compositions are all solution-processed in the framework of multilayered structure, where QD emitting layer is sandwiched by hybrid charge transport layers of poly(9-vinlycarbazole) and ZnO nanoparticles. The device performance such as luminance and efficiency is found to be strongly dependent on the composition of CIGS QDs, and well interpreted by the device energy level diagram proposed through the determination of QD valence band minima by photoelectron emission spectroscopic measurement.

Sensitive Organophosphorus and Carbamate Pesticides Biosensor Based on Acetylcholinesterase and CdZnSe/ZnS Ternary Alloy Quantum Dots

This report presents the results of ternary alloy quantum dots (TQDs) manufacturing and its superior optical properties to fabricate the biosensor for pesticide detection. The explanation for the changes in PL intensity based on the change of electronic charges that alters the pH value of the surrounding environment, and the types of interaction on the surface of CdZnSe/ZnS TQDs were discussed. We show the decomposition process of the indicator (ATCh) with the catalysis from acetylcholinesterase enzyme (AChE) that inhibited by organophosphorus and carbamate pesticides including Trichlorfon (TF), Cypermethrin (CH), Abamectin (AT), and Carbosulfan (CS) with concentrations from 0.05 ppm to 10 ppm.