Recent Progress on Spectroscopy of Lanthanide Ions Incorporated in Semiconductor Nanocrystals

Doping luminescent lanthanide ions into semiconductor nanocrystals is an ideal approach for developing nanodevices for various applications. Quantum confinement effects are expected for lanthanide ions doped in small semiconductor nanocrystals. The most recent progress on the synthesis and spectroscopy of lanthanide ions in various semiconductor nanocrystals such as Ⅱ -Ⅵ, Ⅲ-Ⅴ and Ⅳ-Ⅵ families were systematically reviewed, focusing on our recent findings on the optical spectroscopy of Eu^3 ＋ doped in ZnO and TiO2 nanocrystals by wet chemical synthesis. The energy transfer from the band-gap excitation to lanthanides further confirmed that lanthanide ions could be successfully incorporated into the lattice sites in spite of the mismatch in ionic radii.

Telluride semiconductor nanocrystals:progress on their liquid-phase synthesis and applications

The synthesis of colloidal telluride semiconductor nanocrystals(CT-SNCs)is more challenging than that of chalcogenides,due to the smaller electron affinity of tellurium than that of sulfur and selenium,which is attributed to its metalloid property.While some new potential strategies were developing with the increasing demand of CT-SNCs,the cation exchange reaction(CER)has particularly become a new strategy to synthesize highquality CT-SNCs and their corresponded hetero-nanostructures.This review summarizes the synthesis strategies of CT-SNCs,including traditional methods and new methods with emphasis on CERs,and their resulting CTSNCs with well-controlling size,shape,composition,crystallization and hetero-interfaces cooperatively.The progressive synthesis methods give rise to the excellent optical properties of CT-SNCs.This review also covers the recent progress of their applications in the field of photoelectric detection,catalysis,batteries and biology.The new hybrid CT-SNCs nanostructures are also emphasized and systematically discussed due to their enhanced properties.

Photoluminescence Characteristics of ZnCuInS-ZnS Core-Shell Semiconductor Nanocrystals

The photoluminescence （PL） characteristics of ZnCuInS quantum dots （Q, Ds） with varying ZnS shell thicknesses of O, 0.5, and 1.5 layers are investigated systemically by time-correlated single-photon counting measurements and temperature-dependent PL measurements. The results show that a ZnS shell thickness of 1.5 layers can effectively improve the PL quantum yield in one order of magnitude by depressing the surface trapping states of the core ZnCuInS QDs at room temperature. However, the PL measurements at the elevated temperature reveal that the core-shell nanocrystals remain temperature-sensitive with respect to their relatively thin shells. The temperature sensitivity of these small-sized single-layered core-shell nanocrystals may find applications as effective thermometers for the in vivo detection of biological reactions within cells.

Synaptic devices based on semiconductor nanocrystals

To meet a growing demand for information processing,brain-inspired neuromorphic devices have been intensively studied in recent years.As an important type of neuromorphic device,synaptic devices have attracted strong attention.Among all the kinds of materials explored for the fabrication of synaptic devices,semiconductor nanocrystals(NCs)have become one of the preferred choices due to their excellent electronic and optical properties.In this review,we first introduce the research background of synaptic devices based on semiconductor NCs and briefly present the basic properties of semiconductor NCs.Recent developments in the field of synaptic devices based on semiconductor NCs are then discussed according to the materials employed in the active layers of the devices.Finally,we discuss existing problems and challenges of synaptic devices based on semiconductor NCs.

A Novel Photothermal Nanocrystals of Cu_7S_4 Hollow Structure for Efficient Ablation of Cancer Cells

Cu2-x S nanocrystals(NCs), characterized by low cost, low toxicity, high stability and high photothermal conversion efficiency, provide promising platforms as photothermal agents. Herein, a novel twostep synthesis has been developed for Cu7S4 nanocrystals with hollow structure using the as-prepared copper nanoparticles as starting a solid precursor followed by hot-injection of sulfide source.The Cu7S4 NCs exhibit intense absorption band at Near-infrared(NIR) wavelengths due to localized surface plasmon resonance(LSPR)mode, which can effectively convert 980 nm-laser energy into heat.Moreover, the localized high temperature created by Cu7S4 NCs under NIR irradiation could result in efficient photothermal ablation(PTA) of cancer cells in vivo, demonstrating a novel and promising photothermal nanomaterials.

Sensitization of Hydrothermally Grown Single Crystalline TiO2 Nanowire Array with CdSeS Nanocrystals for Photovoltaic Applications

An oriented array of electron transporting nanowires, grown directly on a transparent conductor constitutes an optimal architecture for efficient photovoltaic applications. In addition, semiconductor nanocrystals can work as efficient light absorbers because of their tunable optical properties. In this paper, we use an oriented array of TiO2 nanowires grown directly on a transparent conductive electrode and subsequently sensitized with colloidally grown CdSeS nanocrystal quantum dots （QDs）, using an efficient bi-linker assisted methodology, to demonstrate photovoltaic cells. Upon excitation with light, exciton dissociation takes place at the nanowire-nanocrystal interface, after which, electrons are transported to the fluorine-doped tin oxide （FTO） electrode via single-crystalline TiO2 nanowire channels. We demonstrate that an ex situ ligand exchange of QDs followed by sensitization on oxygen-plasma treated TiO2 nanowires results in enhanced loading of QDs, as compared to the in situ ligand exchange approach. An array of 1μm long TiO2 nanowire sensitized with CdSeS nanocrystals exhibits photovoltaic effects with a short-circuit current of 2-3 mA/cm2, an open circuit voltage of 0.6-0.7 V and a fill factor of 52-5%, resulting in devices with efficiencies of up to 0.6%.

Shell-thickness dependent optical properties of CdSe/ CdS core/shell nanocrystals coated with thiol ligands

Using CdSe/CdS core/shell nanocrystals with 1-10 monolayers of CdS shell as the model system, we studied effects of thiol ligands on optical properties of the nanocrystals. The core/shell nanocrystals with original ligands possessed near unity photoluminescence （PL） quantum yield and single-exponential PL decay dynamics. The effects of thiol ligands on optical properties were found to depend on the shell thickness, environment （with/without oxygen）, and excitation power （single- or multi-exciton）. Systematic and quantitative results reported in this work should provide necessary information for fundamental understanding and technical applications of quantum dots （QDs） coated with thiol ligands.

Preparation of CdTe Nanocrystals Doped Fluorescent Silica Spheres by Sol-gel Method and Their Surface Modification via Thiol-ene Chemistry

A thcile one-step sol-gel method was used to prepare CdTe nanocrystals（NCs） doped silica microspheres with luxuriant thiol group on their surface using 3-mercaptopropyl trimethoxysilane（MPTMS） as organosilane in the aqueous solution. As the ligand and organosilane, MPTMS ensured the doping efficiency of CdTe NCs by ligand exchange and a large thiol group exposed to the solution to activate the surface of silica microspheres. The remodeled sol-gel process was performed at a lower temperature, which protected the thiol groups from degradation. Meanwhile, the particle size and size distribution can be controlled by varying synthesis conditions, such as the stirring rate and the reaction temperature. This user-friendly method provides a plattbrm tbr immobilization of chemical groups such as carboxyl for combination of bioactive and diagnostic molecules at the surface of CdTe NCs doped silica micro- spheres through thiol-ene chemistry for high-throughput microarrays.

A perspective on functionalizing colloidal quantum dots with DNA

This perspective provides an overview of the techniques that have been developed for the conjugation of DNA to colloidal quantum dots （QDs）, or semiconductor nanocrystals. Methods described include： ligand exchange at the QD surface, covalent conjugation of DNA to the QD surface ligands, and one-step DNA functionalization on core QDs or during core/shell QD synthesis in aqueous solution, with an emphasis on tile most recent progress in our lab. We will also discuss emerging trends in DNA-functionalized QDs for potential applications.

Facile synthesis of ternary AgInS_(2)nanowires and their self-assembly of fingerprint-like nanostructures

Nanowires(NWs)and self-assemble nanostructures made of chalcogenide semiconductor nanocrystals(NCs)are of great interests to the fundamental studies and practical applications.In this study,we reported a seeded-mediated growth of AgInS_(2)NWs and their intriguing self-assembly nanostructures with fingerprint-like shape.The key to the formation and self-assembly of AgInS_(2)NWs was the presence of In-S species that was a type of molecular metal chalcogenide complexes,serving as specific inorganic ligands for the growth of NWs and cross-linker molecules for the self-assembly of fingerprint-like nanostructures.Systematic studies were carried out to investigate the reaction factors,including the thermodynamics,amount and type of In precursors,and 1-dodecanethiol usage,to the success of the desired products.

Optical properties and applications of two-dimensional CdSe nanoplatelets

Compared with zero-dimensional quantum dots and one-dimensional nanorods,two-dimensional nanoplatelets exhibit many unique optical properties.Due to strong quantum confinement in only one direction and the large lateral size,the CdSe nanoplatelets show large exciton binding energy,giant oscillator strength,narrow emission,large absorption cross-section,and large optical gain.In this review,the development of synthesis technology of nanoplatelets is first briefly introduced.Subsequently,the optical properties of CdSe nanoplatelets and their heterostructures are reviewed,including absorption and photoluminescence,carrier dynamics,optical gain,and nonlinear properties.These optical properties are affected by size,material and structure.At last,the main applications of CdSe nanoplatelets in recent years are introduced,including light-emitting diodes,lasers,light harvesting,photocatalysis,and sensing.