Kheng Swee Leck

Full Visible Range Covering InP/ZnS Nanocrystals with High Photometric Performance and Their Application to White Quantum Dot Light-Emitting Diodes

lasers, [ 9–11 ] biomedical imaging, [ 12,13 ] and sensors. [ 14,15 ] Currently, CdSe NCs as the workhorse have been well developed for such uses. [ 16–32 ] Despite their apparent advantages (high emission quantum yields, narrow emission line width, good photostability, etc. [ 33–37 ] ), the intrinsic toxicity of CdSe NCs makes them environmentally restricted, which has thus cast a doubtful future for their practical applications. [ 38,39 ] Indium phosphide (band gap: 1.35 eV) is considered as the ideal alternative material, which offers a similar emission wavelength range but without intrinsic toxicity. [ 40–51 ] Previous studies have demonstrated that InP NCs can be well used in white LEDs for improving their CRI. For example, Nann et al. reported a solidstate white LED with a CRI value up to 86 by adding InP/ZnS NCs in green together with yellow phosphors. [ 52 ] Recently, a high quantum effi ciency (QE) of InP NCs of close to 70% was realized, [ 46 ] and electroluminescence (EL) emission from InP-based NCs was also reported. [ 53 ] However, there exist crucial problems related to the performance of these InP NCs. Among them are their color purity and emission spectrum tunability, which are much inferior to the well-developed CdSe NCs. The inferior properties of these InP NCs originate from a harsh reaction control owing to the strong coordinating strength of indium ligands. The emission linewidth of the typical InP NCs reported is wider (50–80 nm) than that of CdSe (15–40 nm), which leads to a worse color purity for InP as compared to CdSe. A pioneer work on the synthesis of the InP/ZnS NCs with tunable

Synthesis and nonvolatile memory behaviors of dioxatetraazapentacene derivatives.

Two novel heteroacenes 2,3,9,10-tetra(furan-2-yl)-1,4,8,11-tetraaza-6,13-dioxapentacene (FAOP, 1) and 2,3,9,10-tetra(thiophen-2-yl)-1,4,8,11-tetraaza-6,13-dioxapentacene (TAOP, 2) was successfully synthesized through a one-step condensation reaction, which have been fully characterized by (1)H NMR (nuclear magnetic resonance), (13)C NMR, FT-IR (Fourier transform infrared spectroscopy), and HRMS (high-resolution mass spectrum). The sandwich-structure memory devices have been fabricated using FAOP (1) and TAOP (2) as active layers, showing a typical bipolar resistive switching (RS) behavior in positive and negative regions.

Blue liquid lasers from solution of CdZnS/ZnS ternary alloy quantum dots with quasi-continuous pumping

A blue (ca. 440 nm) liquid laser with an ultra-low threshold through which quasi-continuous wave pumping is accessible is achieved by engineering unconventional ternary CdZnS/ZnS alloyed-core/shell QDs. Such an achievement is enabled by exploiting the novel gain media with minimal defects, suppressed Auger recombination, and large gain cross-section in combination with high-quality-factor whispering gallery mode resonators.

Solution processed tungsten oxide interfacial layer for efficient hole-injection in quantum dot light-emitting diodes.

A highly efficient and stable QLED using an inorganic WO3 nanoparticle film as a hole injection layer is demonstrated.The resulting WO3 nanoparticle-based QLEDs also exhibit superior performance compared to that of the present PEDOT:PSS-based QLEDs. The results indicate that WO3 nanoparticles are promising solution-processed buffer layer materials and serve as a strong candidate for QLED technology towards the practical applications in the next-generation lighting and displays.

A bright cadmium-free, hybrid organic/quantum dot white light-emitting diode

We report a bright cadmium-free, InP-based quantum dot light-emitting diode (QD-LED) with efficient green emission. A maximum brightness close to 700 cd/m2 together with a relatively low turn-on voltage of 4.5 V has been achieved. With the design of a loosely packed QD layer resulting in the direct contact of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) in the device, a ternary complementary white QD-LED consisting of blue component (poly-TPD), green component (QDs), and red component (exciplex formed at the interface between poly-TPD and TPBi) has been demonstrated. The resulting white QD-LED shows an excellent color rendering index of 95.

Quantum Dot Light-Emitting Diode with Quantum Dots Inside the Hole Transporting Layers

We report a hybrid, quantum dot (QD)-based, organic light-emitting diode architecture using a noninverted structure with the QDs sandwiched between hole transporting layers (HTLs) outperforming the reference device structure implemented in conventional noninverted architecture by over five folds and suppressing the blue emission that is otherwise observed in the conventional structure because of the excess electrons leaking towards the HTL. It is predicted in the new device structure that 97.44% of the exciton formation takes place in the QD layer, while 2.56% of the excitons form in the HTL. It is found that the enhancement in the external quantum efficiency is mainly due to the stronger confinement of exciton formation to the QDs.

Stable, Efficient, and All-Solution-Processed Quantum Dot Light-Emitting Diodes with Double-Sided Metal Oxide Nanoparticle Charge Transport Layers

An efficient and stable quantum dot light-emitting diode (QLED) with double-sided metal oxide (MO) nanoparticle (NP) charge transport layers is fabricated by utilizing the solution-processed tungsten oxide (WO3) and zinc oxide (ZnO) NPs as the hole and electron transport layers, respectively. Except for the electrodes, all other layers are deposited by a simple spin-coating method. The resulting MO NP-based QLEDs show excellent device performance, with a peak luminance of 21300 cd/m(2) at the emission wavelength of 516 nm, a maximal current efficiency of 4.4 cd/A, and a low turn-on voltage of 3 V. More importantly, with the efficient design of the device architecture, these devices exhibit a significant improvement in device stability and the operational lifetime of 95 h measured at room temperature can be almost 20-fold longer than that of the standard device.

White light emission from CdTe quantum dots decorated n-ZnO nanorods/p-GaN light-emitting diodes

ZnO-based heterostructured light-emitting diode was fabricated by hydrothermally growing ZnO nanorods on p-type GaN substrate. Blue-violet electroluminescence was observed from the ZnO/GaN diode. The color-tunable CdTe quantum dots (QDs) samples with photoluminescence emission peaks ranging from 550 nm to 660 nm were synthesized. We fabricated two hybrid light-emitting diodes by decorating different CdTe QDs on the ZnO nanorods/GaN diodes, the white light emission was effectively observed from such devices.

Facile Synthesis of Luminescent AgInS2–ZnS Solid Solution Nanorods

higher photon absorption cross-section, [ 4 ] stronger electric dipoles, [ 5 , 6 ] and effi cient one-dimensional electrical transport, [ 7 ] which are related to their anisotropic shape. Over the past few years, a fi ne control over single-component semiconductor nanorods has been achieved by colloidal chemistry routes. [ 8–18 ] However, the growth of multicomponent nanorods has been relatively less developed. This is mainly due to the distinct material components characterized with different physical properties, surface chemistry and morphologies. [ 19 ] The study of multicomponent nanoparticles, consisting of two or more components within each particle, is important both for creating multifunctional nanomaterials and for controlling electronic coupling between nanoscale units. [ 14 ] Recently, great development has been made in the multicomponent nanorods in heterostructures, [ 20–26 ] leading to revolutionary applications in many fi elds such as catalysis, photovoltaic devices, and sensors. For example, Manna et al. [ 25 ] reported the synthesis of CdSe/CdS/ZnS double shell nanorods with high photoluminescence effi ciency biolabeling probes for cell labeling applications. Very recently, highly emissive CdSe/CdS rod in rod core/shell heterostructure with strong linear polarization has been prepared by Banin and co-workers using a seeded-growth approach for potential

Resistive switching in a GaOx-NiOx p-n heterojunction

We report a unidirectional bipolar resistive switching in an n-type GaOx/p-type NiOx heterojunction fabricated by magnetron sputtering at room temperature. The resistive switching behavior coincides with the switching between Ohmic conduction (low resistance) and rectifying behavior (high resistance) of the heterojunction diode. Under external electric field, electromigrated intrinsic defects, such as oxygen vacancies and oxygen ions, accumulate at the pn junction interface and modify the interface barrier, forming or rupturing the filamentary paths between n-GaOx and p-NiOx, leading to the switching between Ohmic and diode characteristics of the device. The device shows good endurance, retention performance, and scaling capability, signaling the potential of a diode-structured resistive switching device for non-volatile memory applications.