The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.

/pdf/towards-a-definition-of-inorganic-nanoparticles-from-an-4qpaj5a6q5.pdf

Towards a definition of inorganic nanoparticles from an environmental, health and safety perspective

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

https://www.mdpi.com/1996-1944/3/4/2260/pdf

Quantum Dots and Their Multimodal Applications: A Review

XPS and optical studies of different morphologies of ZnO nanostructures prepared by microwave methods

One-dimensional electrospun nanofibers of p-type NiO/n-type ZnO heterojunctions with different molar ratios of Ni to Zn were successfully synthesized using a facile electrospinning technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV−vis diffuse reflectance (DR) spectroscopy, resonant Raman spectroscopy, photoluminescence (PL) spectroscopy, and surface photovoltage spectroscopy (SPS) were used to characterize the as-synthesized nanofibers. The results indicated that the p−n heterojunctions formed between the cubic structure NiO and hexangular structure ZnO in the NiO/ZnO nanofibers. Furthermore, the photocatalytic activity of the as-electrospun NiO/ZnO nanofibers for the degradation of rhodamine B (RB) was much higher than that of electrospun NiO and ZnO nanofibers, which could be ascribed to the formation of p−n heterojunctions in the NiO/ZnO nanofibers. In par...

Electrospun Nanofibers of p-Type NiO/n-Type ZnO Heterojunctions with Enhanced Photocatalytic Activity

Graphene quantum dots (GQDs) are a new class of fluorescent reporters promising various novel applications such as bio-imaging, optical sensing and photovoltaics. They have recently attracted enormous interest because of their extraordinary and tunable optical, electrical, chemical and structural properties. However, the widespread use of GQDs is hindered by the poor understanding of their photoluminescence (PL) mechanisms. Using density-functional theory (DFT) and time-dependent DFT calculations, we reveal that the PL of a GQD can be sensitively tuned by its size, edge configuration, shape, attached chemical functionalities, heteroatom doping and defects. In addition, it is discovered that the PL of a large GQD consisting of heterogeneously hybridized carbon network is essentially determined by the embedded small sp2 clusters isolated by sp3 carbons. This study not only provides an explanation to the previous experimental observations but also provides insightful guidance to develop methods for the controllable synthesis and engineering of GQDs.

/pdf/revealing-the-tunable-photoluminescence-properties-of-5gpuv88q55.pdf

Revealing the tunable photoluminescence properties of graphene quantum dots

https://ir.nctu.edu.tw:443/bitstream/11536/13565/1/000230221400011.pdf

Band gap variation of size-controlled ZnO quantum dots synthesized by sol-gel method

ZnO quantum dots (QDs) of controlled sizes have been fabricated by a simple sol-gel method. The blueshift of room-temperature photoluminescence measurement from free exciton transition are observed decreasing with the QD size that is ascribed to the quantum confinement effect. From the resonant Raman scattering, the coupling strength between electron and longitudinal optical phonon, deduced from the ratio of the second- to the first-order Raman scattering intensity, diminishes with reducing the ZnO QD diameter. The size dependence of electron-phonon coupling is principally a result of the Frohlich interaction.

https://ir.nctu.edu.tw:443/bitstream/11536/12129/1/000238717200024.pdf

Size dependence of photoluminescence and resonant Raman scattering from ZnO quantum dots

Both band gap engineering and spatial confinement of optical phonon were observed depending upon the size of ZnO quantum dots at room temperature. Size-dependent blueshifts of photoluminescence and absorption spectra reveal the quantum confinement effect. The measured Raman spectral shift and asymmetry for the E2(high) mode caused by localization of optical phonons agree well with that calculated by using the modified spatial correlation model.

https://ir.nctu.edu.tw:443/bitstream/11536/12131/1/000238717200073.pdf

Band gap engineering and spatial confinement of optical phonon in ZnO quantum dots

Self-assembled secondary ZnO nanoparticles, recognized with the agglomeration of crystalline subcrystals, are successfully synthesized by a simple sol-gel method. TEM images display that one artificial cluster behaves in a single-crystal-like wurtzite structure because subcrystals coagulate as the same crystal orientation. Moreover, from the resonant Raman scattering, the as-grown sample exhibits phonon red shift; meanwhile, the coupling strength between electron and longitudinal optical phonon, determined by the ratio of secondto first-order Raman scattering cross sections, diminishes compared with the samples after postannealing at

https://ir.nctu.edu.tw:443/bitstream/11536/13169/1/000232318500028.pdf

Kuo Feng Lin

Papers

Band gap variation of size-controlled ZnO quantum dots synthesized by sol-gel method

Size dependence of photoluminescence and resonant Raman scattering from ZnO quantum dots

Band gap engineering and spatial confinement of optical phonon in ZnO quantum dots

Enhanced Resonant Raman Scattering and Electron-Phonon Coupling from Self-Assembled Secondary ZnO Nanoparticles