Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

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Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

This Review article summarizes the key advantages of using quantum dots (QDs) as luminophores in light-emitting devices (LEDs) and outlines the operating mechanisms of four types of QD-LED. The key scientific and technological challenges facing QD-LED commercialization are identified, together with on-going strategies to overcome these challenges.

Emergence of colloidal quantum-dot light-emitting technologies

Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2–8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well a...

Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

As new members of carbon material family, carbon and graphene quantum dots (CDs, GQDs) have attracted tremendous attentions for their potentials for biological, optoelectronic, and energy related applications. Among these applications, bio-imaging has been intensively studied, but optoelectronic and energy devices are rapidly rising. In this Feature Article, recent exciting progresses on CD- and GQD-based optoelectronic and energy devices, such as light emitting diodes (LEDs), solar cells (SCs), photodetctors (PDs), photocatalysis, batteries, and supercapacitors are highlighted. The recent understanding on their microstructure and optical properties are briefly introduced in the first part. Some important progresses on optoelectronic and energy devices are then addressed as the main part of this Feature Article. Finally, a brief outlook is given, pointing out that CDs and GQDs could play more important roles in communication- and energy-functional devices in the near future.

Carbon and Graphene Quantum Dots for Optoelectronic and Energy Devices: A Review

Scientists describe a size-selective quantum dot patterning technique that involves kinetically controlling the nanotransfer process without a solvent. The resulting printed quantum dot films exhibit excellent morphology and a well-ordered quantum dot structure. This technique allows fabrication of a 4-inch (or larger) thin-film transistor display with high colour purity and extremely high resolution.

Full-colour quantum dot displays fabricated by transfer printing

Quantum-dot-based LEDs are characterized by pure and saturated emission colours with narrow bandwidth, and their emission wavelength is easily tuned by changing the size of the quantum dots. However, the brightness, efficiency and lifetime of LEDs need to be improved to meet the requirements of commercialization in the near future. Here, we report red, orange, yellow and green LEDs with maximum luminance values of 9,064, 3,200, 4,470 and 3,700 cd m−2, respectively, the highest values reported so far. Solution-processable core–shell quantum dots with a CdSe core and a ZnS or CdS/ZnS shell were used as emissive layers in the devices. By optimizing the thicknesses of the constituent layers of the devices, we were able to develop quantum-dot-based LEDs with improved electroluminescent efficiency (1.1–2.8 cd A−1), low turn-on voltages (3–4 V) and long operation lifetimes. These findings suggest that such quantum-dot-based LEDs will be promising for use in flat-panel displays.

Bright, multicoloured light-emitting diodes based on quantum dots

Although nickel-based alloys are widely used in industries due to their oxidation and corrosion resistance, the pursuit of better performance in harsh environments is still a great challenge. In this work, we developed a sol–gel method to synthesize Ni3Al coating on a nickel alloy, assisted by a post-annealing process, and investigated the oxidation-resistant performance. The coating thickness can be controlled by designing the deposition times, which keep the pure Ni3Al phase stable. In addition, the surface morphologies indicate that the coating is compact without obvious voids or cracks. Furthermore, the oxidation-resistant property of the coating was investigated by carrying out a supercritical water oxidation experiment. The crystalline structure and surface morphology of the samples before and after 72-h oxidation demonstrated the superior oxidation resistance of the coating. This work provides a convenient method to fabricate an oxidation-resistant coating on a nickel-based alloy, which would be significant for prolonging the service life of vessels under oxidation conditions, especially for supercritical water reactions.

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Sol–Gel-Derived Ni3Al Coating on Nickel Alloy for Oxidation Resistance in Supercritical Water Environments

Effects of NH3/O2/N2 premixed flame/mixture on iron-based metal walls have been investigated experimentally. A premixed NH3/O2/N2 flame or mixture formed by a quartz tube burner impinged on the disc-shaped metal test plate, of which the temperature was kept at 550 oC by an infrared lamp heater. As materials for the test plate, SACM645, SUS304 and SUS310S, which are widely used as industrial steels, were examined. After being exposed to either the NH3/O2/N2 flame or mixture for 5 hours, the surface hardness was measured by using a nano indenter. Distributions of nitrogen atom diffused into the metal wall were measured by means of the Electron Probe Micro Analyzer (EPMA) and Secondary Ion Mass Spectrometry (SIMS). In addition, spatial distributions of the NH3 concentration in the NH3/O2/N2 flame and mixture were measured by employing a two-photon absorption laser-induced fluorescence (TALIF) technique. It was found that the surface hardness of the test plates increased significantly after being exposed to the NH3/O2/N2 flame/mixture. The distributions of surface hardness and nitrogen atom concentration show that nitriding occurred by the present NH3/O2/N2 flame/mixture with the equivalent level of the conventional gas nitriding method. Moreover, it is also found that NH3 concentration in the vicinity of the wall plays an important role in the surface hardness increase, and a wider distribution of NH3 can result in a broader surface hardness distribution.
DOI: https://doi.org/10.18573/jae.8

Daoyuan Wang

Papers

Bright, multicoloured light-emitting diodes based on quantum dots

Sol–Gel-Derived Ni3Al Coating on Nickel Alloy for Oxidation Resistance in Supercritical Water Environments

Nitriding Effects of Ammonia Flames on Iron-based Metal Walls