Shell Quantum Dots Research Articles

An optical keypad lock with high resettability based on a quantum dot-porphyrin FRET nanodevice.

Due to their appealing properties, nanomaterials have become ideal candidates for the implementation of computing systems. Herein, an optical keypad lock based on a Förster resonance energy transfer (FRET) nanodevice is developed. The nanodevice is composed of a green-emission quantum dot with a thick silica shell (gQD@SiO2) and peripheric blue-emission quantum dots with ultrathin silica spacer (bQD@SiO2), on which 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin (TSPP) is covalently linked. The nanodevice outputs dual emission-based ratiometric fluorescence, depending on the FRET efficiency of bQD-porphyrin pairs, which is highly sensitive to the metalation of TSPP: values are 59.7%, 44.8%, and 10.1% for bQD-Zn(ii)TSPP, bQD-TSPP, and bQD-Fe(iii)TSPP pairs, respectively. As such, by using the competitive chelation-induced transmetalation of TSPP, the nanodevice is capable of implementing a 3-input keypad lock that is unlocked only by the correct input order of Zn(ii) chelator, iron ions, and UV light. Interestingly, the reversible transmetalation of TSPP permits the reset (lock) operation of the keypad lock with the correct input order of ascorbic acid, Zn(ii), and UV light. Application of the nanodevice is exemplified by the construction of paper and cellular keypad locks, respectively, both of which feature signal readability and/or high resettability, showing high potential for personal information identification and bio-encryption applications.

Study of FRET between Zn-Cu-In-S/ZnS core/shell quantum dots-Cresyl violet dye system

This study reports the fluorescence resonance energy transfer between Zn-Cu-In-S/ZnS core–shell quantum dots and Cresyl Violet dye. The quenching of Zn-Cu-In-S/ZnS core–shell QD (donor) emission and lifetime and simultaneous enhancement in Cresyl Violet (acceptor) emission validates and confirms the non-radiative resonance energy transfer from Zn-Cu-In-S/ZnS QDs to Cresyl violet. The values of spectral overlap, Förster distance, the distance between donor and acceptor pair and FRET efficiency were determined using the steady state as well as time-resolved fluorescence spectroscopic techniques. This study demonstrates that this systemexhibits efficient FRET and can act as a very sensitive chemical sensor. Since Zn-Cu-In-S/ZnS QDs are nontoxic compared to popular cadmium-based quantum dots, the application of FRET in biological systems will be advantageous. It can find vast applications in photonics and biomedical applications.

Purifying single photon emission from giant shell CdSe/CdS quantum dots at room temperature.

Giant shell CdSe/CdS quantum dots are bright and flexible emitters, with near-unity quantum yield and suppressed blinking, but their single photon purity is reduced by efficient multiexcitonic emission. We report the observation, at the single dot level, of a large blueshift of the photoluminescence biexciton spectrum (24 ± 5 nm over a sample of 32 dots) for pure-phase wurtzite quantum dots. By spectral filtering, we demonstrate a 2.3 times reduction of the biexciton quantum yield relative to the exciton emission, while preserving as much as 60% of the exciton single photon emission, thus improving the purity from g2(0) = 0.07 ± 0.01 to g2(0) = 0.03 ± 0.01. At a larger pump fluency, spectral purification is even more effective with up to a 6.6 times reduction in g2(0), which is due to the suppression of higher order excitons and shell states experiencing even larger blueshifts. Our results indicate the potential for the synthesis of engineered giant shell quantum dots, with further increased biexciton blueshifts, for quantum optical applications requiring both high purity and brightness.

Dye-induced photoluminescence quenching of quantum dots: role of excited state lifetime and confinement of charge carriers.

We investigate the role of quantum confinement and photoluminescence (PL) lifetime of photoexcited charge carriers in semiconductor core/shell quantum dots (QDs) via PL quenching due to surface modification. Surface modification is controlled by varying the number of dye molecules adsorbed onto the QD shell surface forming QD-dye nanoassemblies. We selected CuInS2/ZnS (CIS) and InP/ZnS (InP) core/shell QDs exhibiting relatively weak (664 meV) and strong (1194 meV) confinement potentials for the conduction band electron. Moreover, the difference in the emission mechanism gives rise to a long and short excited state lifetime of CIS (ca. 290 ns) and InP (ca. 37 ns) QDs. Dye molecules of different ionic characters (rhodamine 575: zwitterionic and rhodamine 560: cationic) are used as quenchers. A detailed analysis of Stern-Volmer data shows that (i) quenching is generally more pronounced in CIS-dye assemblies as compared to InP-dye assemblies, (ii) dynamic quenching is dominating in all QD-dye assemblies with only a minor contribution from static quenching and (iii) the cationic dye shows a stronger interaction with the QD shell surface than the zwitterionic dye. Observations (i) and (ii) can be explained by the differences in the amplitude of the electronic component of the exciton wavefunction near the dye binding sites in both QDs, which results in the breaking up of the electron-hole pair and favors charge trapping. Observation (iii) can be attributed to the variations in electrostatic interactions between the negatively charged QD shell surface and the cationic and zwitterionic dyes, with the former exhibiting a stronger interaction. Moreover, the long lifetime of CIS QDs facilitates us to easily probe different time scales of the trapping processes and thus differentiate the origins of static and dynamic quenching components that appear in the Stern-Volmer analysis.

Giant Shell Quantum Dots for Color Conversion and as Active Material in QLED

Giant Shell Quantum Dots for Color Conversion and as Active Material in QLED

InP/ZnSeS/ZnS Core–Shell Quantum Dots as Novel Saturable Absorbers in Mode‐Locked Fiber Lasers

AbstractIn this study, red light emitting InP/ZnSeS/ZnS quantum dots (QDs) are prepared by thermal injection method. The results show that the InP/ZnSeS/ZnS QDs saturable absorbers (SA) have good nonlinear saturable absorption properties with modulation depth of 24.2% and saturation intensity of 0.08 KW cm−2. Then the QD SAs are applied to the erbium‐doped fiber laser (EDFL) ring cavity system, and a mode‐locked laser pulse with a pulse width of 635 fs is generated. In addition, the pulse width is determined by the carrier recovery time, which is closely related to the defect density in the material. A large number of defects are eliminated in the QDs by hydrogen fluoride (HF) treatment, and the pulse width is reduced from 635 to 450 fs. Results of time‐resolved photoluminescence and ultrafast transient absorption spectroscopy (TAS) show that HF treatment indeed reduces defects in InP/ZnSeS/ZnS QDs, indicated by the decrease of the carrier recovery time. This is different from the reported 2D SA materials, which usually reduce the carrier recovery time by increasing the defect density. This study will inspire new applications of QDs in ultrafast photonics and nonlinear optics.

Deterministic topological defects and quantum dot assembly in a nematic liquid crystalline medium

Liquid crystal (LC) materials exhibit interesting electro-optic switching and molecular ordering properties. Furthermore, the addition of chemically compatible active emitters such as core-shell quantum dots (QD) in a LC medium allows optical as well as dielectric tuning in an anisotropic, reconfigurable ordered medium. Order in a nematic LC phase is characterized by an orientational order parameter. In this work, we demonstrate the use of patterned substrates to generate arrays of integer topological defects in a nematic LC medium doped with cadmium selenide (core) cadmium sulfide (shell) core–shell QDs. We demonstrate the formation of metastable air-pillar-induced integer topological defects (TDs) in relatively thinner 9 μm LC sandwich cells, and the formation of field-induced TDs in thicker (25 μm) cells. Simultaneously, the self-assembly of core-shell QDs into square arrays on the patterned substrates is discussed, highlighting potential electro-optic device applications. The surfactant hexadecyltrimethylammonium bromide (CTAB) is found to play a significant role in LC TD formation as well as QD spatial organization at the optimized concentration. Self-assembly and ordering of single- and multi-component LCs within structured devices is a highly relevant problem for modern optoelectronic devices. This work opens new possibilities for classical as well as quantum light sources which require spatially ordered optical emitters in a reconfigurable dielectric medium at a micron-scale.

Development of a Highly Specific Fluoroimmunoassay for the Detection of Doxycycline Residues in Water Environmental and Animal Tissue Samples.

Doxycycline (DOX) and its metabolite residues in food and the environment pose a serious threat to human health and the ecological environment. In this work, a novel method, termed competitive fluoroimmunoassays (cFIA), based on monoclonal antibody (mAb) bio-conjugated CdSe/ZnS core-shell quantum dots (QDs), was developed for sensitive and rapid bioanalyses of DOX in natural water and commercial meats. After the optimization of the experimental conditions, 1 μg mL-1 of coating antigen and 0.5 μg mL-1 of QD-labeled mAb were used for the establishment of the cFIA. With this assay, the 50% inhibition concentration was found to be 0.35 ng mL-1 of DOX in phosphate-buffered saline samples, and the limit of detection was 0.039 ng mL-1 with minor cross-reactivity to other tetracycline members. The recoveries from natural water and commercial meats spiked with DOX concentrations of 10-600 ng mL-1 were 81.3-109.8%, and standard deviation were all below 12%. Levels measured with the QD-cFIA for thirty authentic samples were confirmed by high-performance liquid chromatography with good correlations. These results indicate that QD-cFIA is sultable for the rapid and quantitative detection of DOX residue in environmental and food samples.

Design and simulation of type-I graphene/Si quantum dot superlattice for intermediate-band solar cell applications

Recent experiments suggest graphene-based materials as candidates for use in future electronic and optoelectronic devices. In this study, we propose a new multilayer quantum dot (QD) superlattice (SL) structure with graphene as the core and silicon (Si) as the shell of QD. The Slater–Koster tight-binding method based on Bloch theory is exploited to investigate the band structure and energy states of the graphene/Si QD. Results reveal that the graphene/Si QD is a type-I QD and the ground state is 0.6 eV above the valance band. The results also suggest that the graphene/Si QD can be potentially used to create a sub-bandgap in all Si-based intermediate-band solar cells (IBSC). The energy level hybridization in a SL of graphene/Si QDs is investigated and it is observed that the mini-band formation is under the influence of inter-dot spacing among QDs. To evaluate the impact of the graphene/Si QD SL on the performance of Si-based solar cells, we design an IBSC based on the graphene/Si QD (QDIBSC) and calculate its short-circuit current density (Jsc) and carrier generation rate (G) using the 2D finite difference time domain (FDTD) method. In comparison with the standard Si-based solar cell which records Jsc = 16.9067 mA/cm2 and G = 1.48943 × 1028 m−3⋅s−1, the graphene/Si QD IBSC with 2 layers of QDs presents Jsc = 36.4193 mA/cm2 and G = 7.94192 × 1028 m−3⋅s−1, offering considerable improvement. Finally, the effects of the number of QD layers (L) and the height of QD (H) on the performance of the graphene/Si QD IBSC are discussed.Graphical abstract

Physico-Chemical Transformation and Toxicity of Multi-Shell InP Quantum Dots under Simulated Sunlight Irradiation, in an Environmentally Realistic Scenario.

Quantum dots (QDs) are widely used in optoelectronics, lighting, and photovoltaics leading to their potential release into the environment. The most promising alternative to the highly toxic cadmium selenide (CdSe) QDs are indium phosphide (InP) QDs, which show reduced toxicity and comparable optical and electronic properties. QD degradation leads to the release of toxic metal ions into the environment. Coating the QD core with robust shell(s) composed of another semi-conductor material enhances their properties and protects the QD from degradation. We recently developed double-shelled InP QDs, which proved to be less toxic than single-shell QDs. In the present study, we confirm their reduced cytotoxicity, with an LC50 at 77 nM for pristine gradient shell QDs and >100 nM for pristine thin and thick shell QDs. We also confirm that these three QDs, when exposed to simulated sunlight, show greater cytotoxicity compared to pristine ones, with LC50 ranging from 15 to 23 nM. Using a combination of spectroscopic and microscopic techniques, we characterize the degradation kinetics and transformation products of single- and double-shell QDs, when exposed to solar light at high temperature, simulating environmental conditions. Non-toxic pristine QDs degrade to form toxic In–phosphate, In–carboxylate, Zn–phosphate, and oxidized Se, all of which precipitate as heterogeneous deposits. Comparison of their degradation kinetics highlights that the QDs bearing the thickest ZnS outer shell are, as expected, the most resistant to photodegradation among the three tested QDs, as gradient shell, thin shell, and thick shell QDs lose their optical properties in less than 15 min, 60 min, and more than 90 min, respectively. They exhibit the highest photoluminescence efficiency, i.e., the best functionality, with a photoluminescence quantum yield in aqueous solution of 24%, as compared to 18% for the gradient shell and thin shell QDs. Therefore, they can be considered as safer-by-design QDs.

(Digital Presentation) Characterization of Light Emission Properties of Impurity Doped Ge/Si Core–Shell Quantum Dots

Si–based quantum dots (QDs) have attracted much attention as an active element in Si-based optoelectronic applications because their light emission properties due to carrier confinement have potential to combine photonic processing with electronic processing on a single chip. We have focused on CVD formation and characterization of Si-QDs with Ge core and reported their photoluminescence (PL) properties attributable to type II energy-band alignment between the Ge–core and the Si-shell [1-2]. In addition, we have also demonstrated stable electroluminescence in the near–infrared region from diode structures having a 3–fold stacked Si–QDs with Ge core with an areal dot density of ~2.0×1011 cm−2 under pulsed bias applications [3]. One of the possible ways to enhance the radiative recombination rate and the improve the light emission efficiency is to reduce non–radiative centers and to increase carrier density by impurity doping into the QDs. In this work, in extending our research work to valency-controlled Si–QDs with Ge core, we have studied the effects of boron– and phosphorus–doping to the Ge core on PL properties.A highly dense layer of Si–QDs with Ge core was formed by controlling thermal decomposition of GeH4 and SiH4 alternately on thermally–grown ~2.0 nm–thick SiO2. During the Ge deposition, delta doping of boron and phosphorus atoms in QDs was carried out by pulse injection using 1% B2H6 and 1% PH3 diluted with He, respectively. No changes in dot size and areal dot density with B or P doping were confirmed by AFM topographic images. Under photoexcitation of undoped QDs with a 979–nm line from a semiconductor laser, a broad PL spectrum, which consists of four Gaussian components originating from radiative recombination through quantized states in QDs, were observed in the energy range from 0.62 to 0.85 eV even at room temperature. For the doped QDs, in addition to the four components seen in undoped QDs, relatively-narrow components peaked at ~0.64 eV and ~0.68eV were observed with B-doping and with P-doping to the Ge core, respectively. Notice that, with an increase in B2H6 pulse injection from 1 to 4 times, the integrated PL intensity was enhanced by a factor of 1.4 to 2.4 compared to that of the undoped QDs while no significant change in spectral shape was observable. This can be interpreted in terms of an increase in the number of holes with B-doping to the Ge core since the carrier recombination rates is proportional to the product of the number of electrons and holes confined in each of QDs under weak photoexcitation.AcknowledgementsThe authors wish to thank Dr. Akio Ohta for his contribution to the measurements. This work was supported in part by Grant–in–Aid for Scientific Research (A) 19H00762, 21H04559, and Fund for the Promotion of Joint Intentional Research [Fostering Joint International Research (A)] 18KK0409 of MEXT Japan.

Magnetic/fluorescent dual-modal lateral flow immunoassay based on multifunctional nanobeads for rapid and accurate SARS-CoV-2 nucleocapsid protein detection

The SARS-CoV-2 pandemic has posed a huge challenge to rapid and accurate diagnosis of SARS-CoV-2 in the early stage of infection. In this work, we developed a novel magnetic/fluorescent dual-modal lateral flow immunoassay (LFIA) based on multifunctional nanobeads for rapid and accurate determination of SARS-CoV-2 nucleocapsid protein (NP). The multifunctional nanobeads were fabricated by using polyethyleneimine (PEI) as a mediate shell to combine superparamagnetic Fe3O4 core with dual quantum dot shells (MagDQD). The core-shell structure of MagDQD label with high loading density of quantum dots (QDs) and superior magnetic content realized LFIA with dual quantitative analysis modal from the assemblies of individual single nanoparticles. The LFIA integrated the advantages of magnetic signal and fluorescent signal, resulting excellent accuracy for quantitative analysis and high elasticity of the overall detection. In addition, magnetic signal and fluorescent signal both had high sensitivity with the limit of detection (LOD) as 0.235 ng mL−1 and 0.012 ng mL−1, respectively. The recovery rates of the methods in simulated saliva samples were 91.36%–103.60% (magnetic signal) and 94.39%–104.38% (fluorescent signal). The results indicate the method has a considerable potential to be an effective tool for diagnose SARS-CoV-2 in the early stage of infection.

Characterization of Light Emission Properties of Impurity Doped Ge/Si Core–Shell Quantum Dots

We have fabricated valency-controlled Si-QDs with Ge-core with an areal density as high as ~1011 cm-2 on ultrathin SiO2 and studied the effect of phosphorus- and boron-doping on Ge-core from their PL properties. During the Ge deposition, delta doping of phosphorus or boron atoms in QDs was carried out by pulse injection using 1% PH3 or B2H6 diluted with He, respectively. No changes in dot size and density with either P- or B-doping were confirmed by AFM topographic images. Under photoexcitation of undoped QDs with a 976-nm line from a semiconductor laser, broad PL spectra consisting of four Gaussian components originating from radiative recombination through quantized states in QDs were observed in the energy range from 0.62 to 0.85 eV without impurity doping even at room temperature. In the doped QDs, relatively-narrow components peaked at ~0.68 eV and ~0.64eV were observed with P-doping and with B-doping to Ge-core, respectively, in addition to the four components seen in undoped QDs. It is interesting noted that, with an increase in B2H6 pulse injection from 1 to 4 times, the integrated PL intensity was enhanced by a factor of 1.4 to 2.4 compared to that of the undoped QDs while no significant change in spectral shape was observable. This can be interpreted in terms of an increase in the number of holes with B-doping to the Ge core since the carrier recombination rates is proportional to the product of the number of electrons and holes confined in QD under weak photoexcitation.

Charge transport in quantum dot sensitized solar cells: A mathematical model

In this paper, charge transport in quantum dot (QD) thin films is modeled by considering trap-state assisted tunneling among the QD thin films. Multiple parameters associated with traps like density, position, and capture/emission rates which can significantly affect tunneling, have been considered in the model. The model is further extended to the quantum dot sensitized solar cells (QDSSC), and the effects of tunneling rate variation in accordance with the trap-states at the QD-QD interfaces and/or in the shell of QDs is analyzed. In the proposed model, multiple silicon QD layers as active material are considered, which are sandwiched between ZnO as electron transport layer (ETL) and a MoO3 as hole transport layer (HTL). The model couples drift–diffusion framework for charge transport in ETL and HTL, and a system of rate equations for carrier dynamics among the QDs and their interfaces with ETL and HTL. Our analysis shows that the variations in trap-state concentration significantly affect the charge extraction and recombination scenario in the active layer of QDSSC, consequently producing a direct impact on device characteristics.

Silica Shell Thickness-Dependent Fluorescence Properties of SiO2@Ag@SiO2@QDs Nanocomposites.

Silica shell coatings, which constitute important technology for nanoparticle (NP) developments, are utilized in many applications. The silica shell’s thickness greatly affects distance-dependent optical properties, such as metal-enhanced fluorescence (MEF) and fluorescence quenching in plasmonic nanocomposites. However, the precise control of silica-shell thicknesses has been mainly conducted on single metal NPs, and rarely on complex nanocomposites. In this study, silica shell-coated Ag nanoparticle-assembled silica nanoparticles (SiO2@Ag@SiO2), with finely controlled silica shell thicknesses (4 nm to 38 nm), were prepared, and quantum dots (QDs) were introduced onto SiO2@Ag@SiO2. The dominant effect between plasmonic quenching and MEF was defined depending on the thickness of the silica shell between Ag and QDs. When the distance between Ag NPs to QDs was less than ~10 nm, SiO2@Ag@SiO2@QDs showed weaker fluorescence intensities than SiO2@QD (without metal) due to the quenching effect. On the other hand, when the distance between Ag NPs to QDs was from 10 nm to 14 nm, the fluorescence intensity of SiO2@Ag@SiO2@QD was stronger than SiO2@QDs due to MEF. The results provide background knowledge for controlling the thickness of silica shells in metal-containing nanocomposites and facilitate the development of potential applications utilizing the optimal plasmonic phenomenon.

Core–shell carbon-polymer quantum dot passivation for near infrared perovskite light emitting diodes

High-performance perovskite light-emitting diodes (PeLEDs) require a high quality perovskite emitter and appropriate charge transport layers to facilitate charge injection and transport within the device. Solution-processed n-type metal oxides represent a judicious choice for the electron transport layer (ETL); however, they do not always present surface properties and energetics compatible with the perovskite emitter. Moreover, the emitter itself exhibits poor nanomorphology and defect traps that compromise the device performance. Here, we modulate the surface properties and interface energetics between the tin oxide (SnO2) ETL with the perovskite emitter by using an amino functionalized difluoro{2-[1-(3,5-dimethyl-2H-pyrrol-2-ylidene-N)ethyl]-3,5-dimethyl-1H-pyrrolato-N}boron compound and passivate the defects present in the perovskite matrix with carbon-polymer core–shell quantum dots inserted into the perovskite precursor. Both these approaches synergistically improve the perovskite layer nanomorphology and enhance the radiative recombination. These properties resulted in the fabrication of near-infrared PeLEDs based on formamidinium lead iodide (FAPbI3) with a high radiance of 92 W sr−1 m−2, an external quantum efficiency (EQE) of 14%, reduced efficiency roll-off and prolonged lifetime. In particular, the modified device retained 80% of the initial EQE (T80) for 33 h compared to 6 h of the reference cell.

Green AgBiSe2/AgBiS2 core shell quantum dots for stable solar cells by robust SILAR method

Silver bismuth sulphide (AgBiS2) ternary quantum dots are emerging as benign photon absorbers for solar cells. Higher absorption coefficient, easy processability and favourable bandgaps have enabled their potential use in solar cells. In this work, for the first time an in-situ (SILAR - Successive ionic layer adsorption and reaction) water protocol is designed for a stable solar cell device using type-I heterostructure of AgBiSe2/AgBiS2 core shell quantum dots. The cells are fabricated by SILAR method unlike many reports of pre-synthesized quantum dots (QDs) making the device protocol highly robust. Alongside, various low-cost inorganic and solid-state hole transport materials are investigated for eliminating the woes of liquid electrolyte for this device. IV analysis carried out for the device performance reveals the designed heterostructure enhances the power conversion efficiency up to 70% (2.1%) from single junction AgBiS2 (1.4%) device. AgBiS2 acts as an absorber and also allows the confinement of electrons and holes in the core of AgBiSe2. AgBiS2 thus acts as passivating layer for the core, reducing free charge carriers from reaching the trap states located at particle surface. Type-I AgBiSe2/AgBiS2 core shell QDs show least recombination of excited electrons, better stability and higher quantum yield showing potential towards other photo applications like labelling and LEDs.

ZnSe/ZnS Core–Shell Quantum Dots Doped with Mn2+ Ions for Magnetic State-Manipulated Light Sources

ZnSe/ZnS Core–Shell Quantum Dots Doped with Mn²⁺ Ions for Magnetic State-Manipulated Light Sources

Single Conjugated Polymer with Four Stepwise HOMO Levels for Effective Hole Injection Across Large Barrier 1.4 eV to Core–Shell Quantum Dot Layer for Electroluminescence in Inverted QLED

AbstractA novel graded‐HOMO‐level hole transport polymer (g‐HTP) is proposed for the first time with spiro‐polyfluorene (sPF) as the main chain and the three hole‐transporting moieties triphenyl amine (TPA), carbazole (Cz), and N,N′‐dicarbazolyl‐3,5‐benzene (mCP) as side chains for effective hole injection across the large barrier 1.4 eV into the green‐emission core–shell quantum dot (QD) CdSe/ZnS emission layer in inverted QD light‐emitting diode (i‐QLED): ITO/ZnO/QD/HTP/MoO3/Al, in which both oleophilic ligands (OA and TOP) in the QD are partially removed from QD surface by annealing at 270 °C for preventing dissolution by solvent in subsequent coating of hole transport material (HTM) solutions atop and also improving electron and hole mobilities, especially the former. The proposed g‐HTP with various m:n mole ratios of mCP to TPA/Cz moieties along with various reported HTMs (PVK, Poly‐TPD and TFB) are investigated. Among them, the proposed g‐HTP with the comonomer mole ratio 1:1 gives the best performance ηmax 36.1 cd A−1 and Bmax 208 600 cd m−2, which is the highest performance among the reported i‐QLEDs with single hole‐transport layer ever documented. In addition, its efficiency roll off is low from 35.8 cd A−1 at 10 000 cd m−2 to 31.1 cd A−1 at 100 000 cd m−2.

Improved Characteristics of CdSe/CdS/ZnS Core-Shell Quantum Dots Using an Oleylamine-Modified Process.

CdSe/CdS with ZnS/ZnO shell quantum dots (QDs) are synthesized by a one-pot method with various oleylamine (OLA) contents. The crystal structures of the QDs were analyzed by X-ray diffractometry, which showed ZnS diffraction peaks. It was represented that the ZnS shell was formed on the surface of the CdSe/CdS core. Interestingly, QDs with a high OLA concentration exhibit diffraction peaks of ZnS/ZnO. As a result, the thermal stability of QDs with ZnS/ZnO shells exhibits better performance than those with ZnS shells. In addition, the photoluminescence intensity of QDs with ZnS/ZnO shells shows a relatively slow decay of 7.1% compared with ZnS shells at 85 °C/85% relative humidity aging test for 500 h. These indicate that QDs with different OLA modifications can form ZnS/ZnO shells and have good stability in a harsh environment. The emission wavelength of QDs can be tuned from 505 to 610 nm, suitable for micro-LED display applications.