SnO2 quantum dots (QDs) and ultrathin nanowires (NWs) with diameters of approximately 0.5-2.5 and approximately 1.5-4.5 nm, respectively, were controllably synthesized in a simple solution system. They are supposed to be ideal models for studying the continuous evolution of the quantum-confinement effect in SnO2 1D --> 0D systems. The observed transition from strong to weak quantum confinement in SnO2 QDs and ultrathin NWs is interpreted through the use of the Brus effective-mass approximation and the Nosaka finite-depth well model. Photoluminescence properties that were coinfluenced by size effects, defects (oxygen vacancies), and surface capping are discussed in detail. With the SnO2 QDs as building blocks, various 2D porous structures with ordered hexagonal, distorted hexagonal, and square patterns were prepared on silicon-wafer surfaces and exhibited optical features of 2D photonic crystals and enhanced gas sensitivity.

Perovskite and chalcogenide quantum dots (QDs) are important nano semiconductors. It has been a challenge to synthesize heterostructural QDs combining perovskite and chalcogenide with tailorable photoelectronic properties. In this report, heterostructural CsPbX3-PbS (X = Cl, Br, I) QDs were successfully synthesized via a room temperature in situ transformation route. The CsPbX3-PbS QDs show a tunable dual emission feature with the visible and near-infrared (NIR) photoluminescence (PL) corresponding to CsPbX3 and PbS, respectively. Typically, the formation and evolution of the heterostructural CsPbBr3–PbS QDs with reaction time was investigated. Femtosecond transient absorption spectroscopy (TAS) was applied to illuminate the exciton dynamics in CsPbBr3–PbS QDs. The mild synthetic method and TAS proved perovskite to PbS energy transfer may pave the way toward highly efficient QD photovoltaic and optoelectronic devices.

Inorganic CsPbX (X = Cl, Br, I, or hybrid among them) perovskite quantum dots (IPQDs) are promising building blocks for exploring high performance optoelectronic applications. In this work, the authors report a new hybrid structure that marries CsPbX IPQDs to silicon nanowires (SiNWs) radial junction structures to achieve ultrafast and highly sensitive ultraviolet (UV) detection in solar-blind spectrum. A compact and uniform deployment of CsPbX IPQDs upon the sidewall of low-reflective 3D radial junctions enables a strong light field excitation and efficient down-conversion of the ultraviolet incidences, which are directly tailored into emission bands optimized for a rapid photodetection in surrounding ultrathin radial p-i-n junctions. A fast solar-blind UV detection has been demonstrated in this hybrid IPQD-NW detectors, with rise/fall response time scales of 0.48/1.03 ms and a high responsivity of 54 mA W @200 nm (or 32 mA W @270 nm), without the need of any external power supply. These results pave the way toward large area manufacturing of high performance Si-based perovskite UV detectors in a scalable and low-cost procedure.

Perovskite structured CsPbX (X = Cl, Br or I) quantum dots (QDs) have attracted great attention in the past few years for appealing application potentials in photovoltaic and optoelectronic devices. In this report, the CsPbX QDs are shown to perform as a new probe for metal ions with high sensitivity, high selectivity and instant response by the quenching or enhancing of the photoluminescence (PL). Through experimental and calculation efforts, the probing mechanisms are investigated. A wide probing window for Cu and Yb ions ranging from 2 × 10 to 2 × 10 m is exhibited for CsPbBr QDs. In practice, the CsPbBr QDs are successfully applied for fast probing Cu ions in edible oils and vehicle lubricating oils with the precision consistent to the values measured by inductively coupled plasma (ICP). Thus, it provides a promising powerful tool in detecting certain metal ions in biological and industrial organic solution systems.

Low dimensional semiconductor nanomaterials have shown their tailorable properties for a variety of promising applications in decades. Here a general strategy to synthesize all-inorganic CsPbX 3 (X = Cl, Br, I or their mixture) perovskite 2D nanoplates by introducing additional metal halides MX' 2 or MX' 3 (M = Cu, Zn, Al or Pb, etc.; X' = Cl, Br or I) is reported. These CsPbX 3 perovskite nanoplates have uniform thickness and tunable size, which can be feasibly controlled by the component and ratio of the metal halides, temperature, time, and ligands. The well-defined morphology of the nanoplates makes them ideal building blocks for the self-assembly in the face-to-face and column-by-column arrangement. Compared to the optically isotropic CsPbX 3 nanocubes, the 2D CsPbX 3 nanoplates exhibit remarkable polarized UV-vis absorption and photoluminescence not only in liquid solvent and solid resin matrix, but also in self-assembled films. An optoelectronic photodetector sensitive for linear polarized light is fabricated to demonstrate the proof-of-concept.

Size effects in the oriented-attachment (OA) growth process of Cu nanoseeds were found. Monodispersed Cu nanoseeds with average diameters of 2.2, 3.4, and 5.2 nm were controllably synthesized by the reduction of copper acetate in a boiling solvent and using dodecanethiol (DT) as a stabilizer and sulfur source of sulfide. These Cu nanoseeds were then treated under solvothermal conditions. When the diameters of Cu nanoseeds were smaller than 5 nm, Cu(2)S nanorods with lengths of approximately 30-100 nm and diameters of approximately 2-4 nm were obtained at lower temperatures, and Cu(2)S nanodisks with diameters of approximately 6-13 nm and thicknesses of approximately 2-4 nm were obtained at higher temperatures. Once the diameter of Cu nanoseeds was larger than 5 nm, only irregular particles were obtained, regardless of other conditions. The uniformity, which related to the density of DT on the surface of Cu nanoseeds, was the key for success of self-assembly of the final nanocrystals. High-resolution transmission electron microscopy images demonstrated that these nanorods, nanodisks, and particles were formed by an OA process of Cu nanoseeds into 1D, 2D, and 3D aggregates, which recrystallized into single crystals.

Repeated precipitation of colloidal semiconductor quantum dots (QD) from a good solvent by adding a poor solvent leads to an increasing number of QD oligomers after redispersion in the good solvent. By using density gradient ultracentrifugation we have been able to separate QD monomer, dimer, and trimer fractions from higher oligomers in such solutions. In the corresponding fractions QD dimers and trimers have been enriched up to 90% and 64%, respectively. Besides directly coupled oligomers, QD dimers and trimers were also assembled by linkage with a rigid terrylene diimide dye (TDI) and separated again by ultracentrifugation. High-resolution transmission electron micrographs show that the interparticle distances are clearly larger than those for directly coupled dots proving that the QDs indeed are cross-linked by the dye. Moreover, energy transfer from the QDs to the TDI "bridge" has been observed. Individual oligomers (directly coupled or dye-linked) can be readily deposited on a substrate and studied simultaneously by scanning force and optical microscopy. Our simple and effective scheme is applicable to a wide range of ligand stabilized colloidal nanoparticles and opens the way to a detailed study of electronic coupling in, e.g., QD molecules.

Ultrathin InOOH nanowires with a diameter of approximately 2 nm and a length up to approximately 200 nm have been synthesized by a hydrolysis reaction in a solution system. Their transformations to c-In(2)O(3) nanocrystals and rh-In(2)O(3) nanowires have been investigated. A dissolution-recrystallization (in solution) or size-related decomposition-recrystallization (in air) mechanism is indicated for the former transformation; the size- and surface-determined transformation is proposed for the latter. These results will help to understand and control the phase stability and transformation concerning the nanodimension and surface restrictions, especially for ultrathin nanowires.