Xuyong Yang

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

Highly Flexible, Electrically Driven, Top-Emitting, Quantum Dot Light-Emitting Stickers

Flexible information displays are key elements in future optoelectronic devices. Quantum dot light-emitting diodes (QLEDs) with advantages in color quality, stability, and cost-effectiveness are emerging as a candidate for single-material, full color light sources. Despite the recent advances in QLED technology, making high-performance flexible QLEDs still remains a big challenge due to limited choices of proper materials and device architectures as well as poor mechanical stability. Here, we show highly efficient, large-area QLED tapes emitting in red, green, and blue (RGB) colors with top-emitting design and polyimide tapes as flexible substrates. The brightness and quantum efficiency are 20,000 cd/m(2) and 4.03%, respectively, the highest values reported for flexible QLEDs. Besides the excellent electroluminescence performance, these QLED films are highly flexible and mechanically robust to use as electrically driven light-emitting stickers by placing on or removing from any curved surface, facilitating versatile LED applications. Our QLED tapes present a step toward practical quantum dot based platforms for high-performance flexible displays and solid-state lighting.

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.

Near resonant and nonresonant third-order optical nonlinearities of colloidal InP/ZnS quantum dots

We have investigated the third-order optical nonlinearities of high-quality colloidal InP/ZnS core-shell quantum dots (QDs) using Z-scan technique with femtosecond pulses. The two-photon absorption cross-sections as high as 6.2 × 103 GM are observed at 800 nm (non-resonant regime) in InP/ZnS QDs with diameter of 2.8 nm, which is even larger than those of CdSe, CdS, and CdTe QDs at similar sizes. Furthermore, both of the 2.2 nm and 2.8 nm-sized InP/ZnS QDs exhibit strong saturable absorption in near resonant regime, which is attributed to large exciton Bohr radius in this material. These results strongly suggest the promising potential of InP/ZnS QDs for widespread applications, especially in two-photon excited bio-imaging and saturable absorbing.

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.

Europium (II)-doped microporous zeolite derivatives with enhanced photoluminescence by isolating active luminescence centers.

Solid-state reaction is the most common method for preparing luminescent materials. However, the luminescent dopants in the hosts tend to aggregate in the high-temperature annealing process, which causes adverse effect in photoluminescence. Herein, we report a novel europium (II)-doped zeolite derivative prepared by a combined ion-exchange and solid-state reaction method, in which the europium (II) ions are isolated to a large extent by the micropores of the zeolite. Excited by a broad ultraviolet band from 250 to 420 nm, a strong blue emission peaking at 450 nm was observed for these Eu-embedded zeolites annealed at 800 °C in a reducing atmosphere. The zeolite host with pores of molecular dimension was found to be an excellent host to isolate and stabilize the Eu(2+) ions. The as-obtained europium (II)-doped zeolite derivative showed an approximately 9 fold enhancement in blue emission compared to that of the general europium (II)-doped aluminosilicates obtained by conventional solid-state reaction, indicating that, by isolating active luminescence centers, it is promising to achieve highly luminescent materials. Also, the strong blue emission with broad UV excitation band suggests a potential candidate of phosphor for ultraviolet excited light-emitting diode.

Electrochemically deposited zinc oxide arrays for field emission

Periodic zinc oxide rod arrays were fabricated on patterned templates by electrochemical deposition and were employed as field emitters. The morphology and crystal structure of the zinc oxide array were examined by scanning electron microscopy and x-ray diffraction, respectively. The dependence of the field emission current density J and the applied electric field E presented a two-stage slope behavior in ln(J∕E2)−1∕E plot according to Fowler-Nordheim equation. The mechanism of the electron emission is attributed to the defects in the electrochemically deposited zinc oxide rods.

A Promising Deep Red Phosphor AgLaMo2O8 : Pr3 + with Blue Excitation for White LED Application

A deep red phosphor AgLaMo 2 O 8 :Pr 3+ has been prepared by a conventional solid-state reaction technique. The effects of synthesis temperature and Pr 3+ -doped concentration on the luminescent properties and crystal structures of the compound have been investigated. Its excitation wavelength ranging from 440 to 500 nm fits well with the characteristical emission of commercial blue light-emitting diode (LED) chips. The photoluminescence spectra of AgLaMo 2 O 8 :Pr 3+ exhibit deep red emissions, with the strongest emission peak at 649 nm, and show high color purity properties with the color point of (0.685, 0.315). Due to its good excitation and emission performance, the Pr 3+ -doped AgLaMo 2 O 8 phosphor may be a promising candidate for white LEDs.