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Adopting the concept of one dopant for one color, all the prominent emitting colors in the visible windows are obtained by doping selective dopants (Ag, Cu, Ni, and Cu) in an appropriate host (alloy of Cdx Zn1-x S) with fixed size/composition and bandgap. Analyzing the origin of these emissions the relative position of respective dopant states are correlated., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Among materials produced as colloidal quantum dots (CQDs), HgTe has a special status being the only material covering the whole infrared range from the visible to the THz (0.7–100 µm). This unique property resulting from its electronic structure, combined with an air stability and a capacity for charge conduction has generated consistent and massive efforts to produce and improve HgTe CQDs over the past two decades. Meanwhile, HgTe CQDs offer an infrared platform more advanced than any other colloidal alternatives in the mid‐wave infrared regarding their integration into advanced photonic and optoelectronic applications. Here, the latest developments of HgTe CQDs relative to the material's growth, electron structure modelling, its integration into photonic structures and its transfer as the active material from single element devices toward complex sensors and infrared imagers are reviewed. Finally, a discussion about the potential of this material for industry, rising new challenges beyond economical and production considerations at low technological readiness level, relative to the material and device design, is also included. [ABSTRACT FROM AUTHOR]

The excellent performance of semiconductor nanocrystals as sensitizers for photothermal therapy (PTT) has attracted the attention of many researchers; however, they are hindered by limited bandwidth and complex synthesis. To overcome these limitations, starting with an initial determination of photothermal conductivity, we synthesized and designed molybdenum and Cys-MoO3−x nanoparticles (NPs) for use in the minimally invasive treatment of papillary thyroid carcinoma (PTC), as the NPs are coated only with cysteine molecules. The obtained Cys-MoO2 NPs were used as a PTT reaction drug for topical application to PTC cells. The use of near-infrared photoconductive PTT in combination with low-toxicity biological chemotherapy reached a 90% efficacy for cancer treatment in vitro. The conducted experiments intuitively demonstrate that non-toxic Cys-MoO2 NPs are lethal to the cancer cells under visual (VL, 405 nm) and near-infrared (NIR, 808 nm) laser irradiation and can be precisely controlled. Therefore, this study provides a powerful, safe, and easily modified NP platform for photo-triggered PTC elimination with broad application prospects. Assessment of the ideal damage range indicates a high degree of controllability, allowing the tumor to be precisely targeted while minimizing damage to the surrounding healthy tissue. In conclusion, this study provides a convenient, safe, and powerful NP platform for the near-infrared photo-controlled PTT of PTC cells, which has broad application prospects for the elimination of PTC and other types of cancer. [ABSTRACT FROM AUTHOR]

Surface-functionalized polymer beads encoded with molecular luminophores and nanocrystalline emitters such as semiconductor nanocrystals, often referred to as quantum dots (QDs), or magnetic nanoparticles are broadly used in the life sciences as reporters and carrier beads. Many of these applications require a profound knowledge of the chemical nature and total number of their surface functional groups (FGs), that control bead charge, colloidal stability, hydrophobicity, and the interaction with the environment and biological systems. For bioanalytical applications, also the number of groups accessible for the subsequent functionalization with, e.g., biomolecules or targeting ligands is relevant. In this study, we explore the influence of QD encoding on the amount of carboxylic acid (COOH) surface FGs of 2 µm polystyrene microparticles (PSMPs). This is done for frequently employed oleic acid and oleylamine stabilized, luminescent core/shell CdSe QDs and two commonly used encoding procedures. This included QD addition during bead formation by a thermally induced polymerization reaction and a post synthetic swelling procedure. The accessible number of COOH groups on the surface of QD-encoded and pristine beads was quantified by two colorimetric assays, utilizing differently sized reporters and electrostatic and covalent interactions. The results were compared to the total number of FGs obtained by a conductometric titration and Fourier transform infrared spectroscopy (FTIR). In addition, a comparison of the impact of QD and dye encoding on the bead surface chemistry was performed. Our results demonstrate the influence of QD encoding and the QD-encoding strategy on the number of surface FG that is ascribed to an interaction of the QDs with the carboxylic acid groups on the bead surface. These findings are of considerable relevance for applications of nanoparticle-encoded beads and safe-by-design concepts for nanomaterials. [ABSTRACT FROM AUTHOR]

Charge carrier dynamics essentially determines the performance of various optoelectronic applications of colloidal semiconductor nanocrystals. Among them, two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructures. Herein, we demonstrate that by fine-tuning the core size and the lateral quantum confinement, the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets. In addition, the transfer can be affected by a carrier blocking mechanism, i.e., the filled carriers hinder further possible transfer. Furthermore, we found that the biexciton interaction is oppositely affected by quantum confinement and electron delocalization, resulting in a non-monotonic variation of the biexciton binding energy with the emission wavelength. This work provides new observations and insights into the charge carrier transfer dynamics and exciton interactions in colloidal nanoplatelets and will promote their further applications in lasing, display, sensing, etc. [ABSTRACT FROM AUTHOR]

Nanoshell quantum dots (QDs) represent a novel class of colloidal semiconductor nanocrystals (NCs), which supports tunable optoelectronic properties over the extended range of particle sizes. Traditionally, the ability to control the bandgap of colloidal semiconductor NCs is limited to small-size nanostructures, where photoinduced charges are confined by Coulomb interactions. A notorious drawback of such a restricted size range concerns the fact that assemblies of smaller nanoparticles tend to exhibit a greater density of interfacial and surface defects. This presents a potential problem for device applications of semiconductor NCs where the charge transport across nanoparticle films is important, as in the case of solar cells, field-effect transistors, and photoelectrochemical devices. The morphology of nanoshell QDs addresses this issue by enabling the quantum-confinement in the shell layer, where two-dimensional excitons can exist, regardless of the total particle size. Such a geometry exhibits one of the lowest surface-to-volume ratios among existing QD architectures and, therefore, could potentially lead to improved charge-transport and multi-exciton characteristics. The expected benefits of the nanoshell architecture were recently demonstrated by a number of reports on the CdSbulk/CdSe nanoshell model system, showing an improved photoconductivity of solids and increased lifetime of multi-exciton populations. Along these lines, this perspective will summarize the recent work on CdSbulk/CdSe nanoshell colloids and discuss the possibility of employing other nanoshell semiconductor combinations in light-harvesting and lasing applications. [ABSTRACT FROM AUTHOR]

Transition-metal-doped semiconductor nanocrystals have received significant attention because of their attractive features deeming them invaluable in various technological fields including optoelectronics, bio-photonics, and energy conversion, to name a few. Of particular, these interests are two-dimensional materials with useful optical and magnetic properties combined with their large surface areas opening up new applications in biotechnology. These applications range from multimodal optical and magnetic bioimaging and sensing to measuring the weak magnetic field due to brain waves using their magneto-optic properties stemming from the exchange interaction between the transition metal dopants and the carrier spins. These magnetic 2D materials could also significantly advance the field of spintronics. In this work, we report on a study of the magnetic and magneto-optic properties of colloidal two-dimensional (2D) copper-doped CdSe nanoplatelets (NPLs) that are synthesized using a high-temperature colloidal technique. We carried out optical and circularly polarized magneto-photoluminescence spectrometry to investigate the magnetism in our solution-processed nanostructures doped with copper ion impurities. At cryogenic temperatures, two excitonic features are observed for doped NPLs, which are more prominent compared to the undoped NPLs. Furthermore, the excitonic circular polarization (CP) is recorded as a function of the applied magnetic field (B) and temperature (T). The detailed analysis provides a picture of the magneto-optical behavior of the doped 2D NPLs in the presence of paramagnetic copper ions. This work paves the way for significant advances in bio/nanophotonics where tunable optical and magnetic properties of doped nanoplatelets can be leveraged to make more efficient, flexible, and low-cost devices. [ABSTRACT FROM AUTHOR]

Doping the semiconductor nanocrystals is one of the most effective ways to obtain unique materials suitable for high-performance next-generation optoelectronic devices. In this study, we demonstrate a novel nanomaterial for the near-infrared spectral region. To do this, we developed a partial cation exchange reaction on the HgTe nanoplatelets, substituting Hg cations with Pb cations. Under the optimized reaction conditions and Pb precursor ratio, a photoluminescence band shifts to ~1100 nm with a quantum yield of 22%. Based on steady-state and transient optical spectroscopies, we suggest a model of photoexcitation relaxation in the HgTe:Pb nanoplatelets. We also demonstrate that the thin films of doped nanoplatelets possess superior electric properties compared to their pristine counterparts. These findings show that Pb-doped HgTe nanoplatelets are new perspective material for application in both light-emitting and light-detection devices operating in the near-infrared spectral region. [ABSTRACT FROM AUTHOR]

The low-dimensional cesium bismuth halides are intriguing wide-bandgap semiconductors with fruitful photophysics. However, their photodynamics is rather intricate and remains debated. We study the optical properties of the Cs3Bi2Br9 nanoplatelets (NPLs) by using the combined experimental and first-principles calculation methods. The results indicate that the exhibited dominant blue emission band and weak green band arise from two kinds of shallow color centers. The Cs3Bi2Br9 NPLs exhibit Raman active and inactive vibrational modes that are separately ascribed to the localized lattice waves propagating along the edges and interiors of the quantum well-like bromide–bismuth octahedral frameworks in Cs3Bi2Br9. These findings improve our understanding of the unique photodynamics of these multiple quantum well-like semiconductor nanocrystals. [ABSTRACT FROM AUTHOR]

Colloidal semiconductor nanocrystals, in particular cadmium and lead chalcogenide particles, are pivotal materials in many optoelectronic applications. While synthetic advances in the past decades now allow precise control of their size, shape, and composition, they must be processed from dispersion into functional films for many applications, which presents additional challenges. In this review, recent progresses in the field of nanoparticle self‐assembly into functional thin films with precise control over nanoparticle order and orientation are discussed. A comprehensive overview on characterization methods used in the study of such ordered materials is provided and the gas–liquid interfacial self‐assembly and electric field driven deposition as the two most promising ways to generate superstructures with defined thickness, order, and orientation are discussed. The superstructure–property relationships are then reviewed with emphasis on charge migration through the film and radiative processes. Last, challenges and open questions in the field are addressed. [ABSTRACT FROM AUTHOR]

The mechanism of the influence of ultrasound on the nucleation and growth of A2B6 nanoparticles in a colloidal solution was investigated. The proposed theory is based on an increase in the temperature of the colloidal solution and the diffusion coefficient of the monomer under the influence of ultrasonic cavitation. It was established that ultrasound leads to a decrease in the critical radius of colloidal nanoparticles. And when the radius of nanoparticles exceeds this critical value, their growth is observed. The dependence of the growth rate of CdSe nanoparticles on their radius at different temperatures and intensities of ultrasound was researched. It is shown that at the beginning of nanocrystal growth, an increase in intensity of ultrasound leads to an increase in the growth rate, followed by a sharp decrease. This makes it possible to synthesize colloidal quantum dots that are more uniform in size with the help of ultrasonic treatment. [ABSTRACT FROM AUTHOR]

We demonstrate the high efficiency of quantum dot light-emitting diodes (QLEDs) that consist of a mixed layer of SnO2 nanoparticles (NPs) and quantum dots (QDs). A stable mixture of SnO2 NPs and QDs is prepared in chlorobenzene and then applied to QLEDs with no separate electron transport layer (ETL). QLEDs with such a simplified structure produce a maximum luminance of 142,855 cd/m2, an EQE of 9.42%, and a current efficiency of 41.18 cd/A that result from the improved charge balance of the mixed layer. This produces one of the best device performances of QLEDs with a non-ZnO inorganic ETL, clearly indicating the remarkable promise of using SnO2 NPs as an inorganic ETL for QLEDs. Moreover, the reduction of fabrication steps in this solution-based process proves advantageous to next-generation display technology. [ABSTRACT FROM AUTHOR]

Ligand‐induced chirality in colloidal semiconductor nanocrystals attracts attention because of their tunable chiroptical properties. Here, the induced chirality and circularly polarized luminescence (CPL) are investigated as a function of the CdS shell growth in a range of 2D CdSe/CdS nanoplatelets (NPLs) capped with chiral ligands. Five samples of CdSe/CdS NPLs are synthesized by a one‐pot approach to vary the island‐like shell on a four‐monolayer (4 ML) CdSe NPLs core, which effectively reduces the interfacial strain energy. The successful preparation of L‐/D‐Cysteine‐capped CdSe/CdS NPLs with both tunable circular dichroism (CD) and CPL behaviors and a maximum anisotropic luminance factor (glum) of 5.29 × 10−4 is described. The induced chiroptical response shows a direct relationship with the formation of island‐like shell in the first and second stages and shows a clear signal evolution. In the third stage with a full coating shell, the CD and CPL signals are inversely proportional to the CdS shell thickness. The island‐like shell gives birth to the CPL signal, while the formation of full coating shell decreases the induced chirality. Such chiral and emissive NPLs provide an ideal platform for the rational design of semiconductor nanocrystals with chiroptical properties in areas of biomedicine, polarizers, and new generation of display devices. [ABSTRACT FROM AUTHOR]

Luminescent solar concentrators (LSCs) have recently gained popularity as an effective solution to increase solar energy conversion. Utilizing LSCs together with solar cells can generate more energy at a lower cost than using only solar cells. LSCs operate by utilizing luminophores, molecules that absorb incident solar irradiation and re‐emit photons, and waveguides that redirect emitted photons to the edges of a glass or polymer slab at high concentrations. Many quantum dots (QDs) have been the focus of much research as luminophores for LSCs, owing to their high quantum yields (QYs), controllable absorption/emission spectra, good stability, and ease of synthesis. Various QDs, such as CdSe, PbS, CdS, AgInS2, Si, and C, have been modified to enhance their optical performances in LSCs, often measured by their optical efficiencies, internal/external quantum efficiencies, and power conversion efficiencies. This review appraises the latest developments in colloidal QDs—basic QDs, doped QDs, core/shell QDs, hybrid QDs, and Si‐based QD—for their applications in LSCs. Other factors that enhance an LSC's efficiency, such as altering the polymer matrix and using distributed Bragg reflectors, are discussed. The development of highly efficient, QD‐based LSCs will be essential for increasing solar energy production worldwide. [ABSTRACT FROM AUTHOR]

Colloidal two-dimensional (2D) semiconductor nanocrystals are of great importance due to their remarkable optical and electronic properties. Herein, shape-controllable synthesis of 2D wurtzite CdTe nanoplatelets (NPLs) by simply tailoring the reactivity of a tellurium (Te) precursor is reported. Ribbon-, shield-, and bullet-like 2D CdTe NPLs were prepared by a stepwise conversion from CdTe magic-size nanoclusters (MSNCs) by using Te32–, Te22–, and Te2– polytellurides as the tellurium precursor, respectively. This work not only develops a synthetic strategy capable of synthesising wurtzite CdTe nanoplatelets with controlled shapes by tailoring the reactivity of tellurium precursors but also gives insights into the growth mechanisms of colloidal 2D semiconductor nanocrystals. CdTe nanoplatelets (NPLs) were synthesised by simply tailoring the reactivity of the tellurium (Te) precursor. Ribbon-, shield-, and bullet-like CdTe NPLs were prepared by using Te32–, Te22–, and Te2– polytellurides as the tellurium precursor, respectively. This work develops a synthetic strategy for wurtzite CdTe nanoplatelets with controlled shapes. [ABSTRACT FROM AUTHOR]

To improve quantum dot solar cell performance, it is crucial to make efficient use of the available incident sunlight to ensure that the absorption is maximized. The ability of metal nanoparticles to concentrate incident sunlight via plasmon resonance can enhance the overall absorption of photovoltaic cells due to the strong confinement that results from near-field coupling or far-field scattering plasmonic effects. Therefore, to simultaneously and synergistically utilize both plasmonic effects, the placement of different plasmonic nanostructures at the appropriate locations in the device structure is also critical. Here, we introduce two different plasmonic nanoparticles, Au and Ag, to a colloidal PbS quantum dot heterojunction at the top and bottom interface of the electrodes for further improvement of the absorption in the visible and near-infrared spectral regions. The Ag nanoparticles exhibit strong scattering whereas the Au nanoparticles exhibit an intense optical effect in the wavelength region where the absorption of light of the PbS quantum dot is strongest. It is found that these dual-plasmon layers provide significantly improved short-circuit current and power conversion efficiency without any form of trade-off in terms of the fill factor and open-circuit voltage, which may result from the indirect contact between the plasmonic nanoparticles and colloidal quantum dot films. [ABSTRACT FROM AUTHOR]

Trap states in colloidal quantum dot (QD) solids significantly affect the performance of QD solar cells, because they limit the open‐circuit voltage and short circuit current. The {100} facets of PbS QDs are important origins of trap states due to their weak or missing passivation. However, previous investigations focused on synthesis, ligand exchange, or passivation approaches and ignored the control of {100} facets for a given dot size. Herein, trap states are suppressed from the source via facet control of PbS QDs. The {100} facets of ≈3 nm PbS QDs are minimized by tuning the balance between the growth kinetics and thermodynamics in the synthesis. The PbS QDs synthesized at a relatively low temperature with a high oversaturation follow a kinetics‐dominated growth, producing nearly octahedral nanoparticles terminated mostly by {111} facets. In contrast, the PbS QDs synthesized at a relatively high temperature follow a thermodynamics‐dominated growth. Thus, a spherical shape is preferred, producing truncated octahedral nanoparticles with more {100} facets. Compared to PbS QDs from thermodynamics‐dominated growth, the PbS QDs with less {100} facets show fewer trap states in the QD solids, leading to a better photovoltaic device performance with a power conversion efficiency of 11.5%. [ABSTRACT FROM AUTHOR]

In this paper, we make a review of experimental techniques used in the study of semiconductor quantum dots and focus on the basic principles of optical coherent control of the exciton. We discuss both optical methods of investigation (time-resolved pump-probe, control of p-shell by measuring the photoluminescence from s-level, resonant fluorescence) and a photocurrent technique. Although the last one reduces the coherence of the system, but gives a quantitative measure of it. Special attention is applied to physical properties of self-assembled quantum dots as the methods of production which allow obtaining high-quality nanoparticles in macroscopic quantities. We also discuss our results obtained from colloidal CdSe quantum dots photoluminescence and transmission measurements, and Raman scattering spectra. We witness Stokes shift for an ensemble of nanoparticles that have a fairly broad size distribution. The analysis of the secondary radiation of the CdSe nanoparticles was done to study both processes leading to this energy shift and the loss of exciton polarization. [ABSTRACT FROM AUTHOR]

The upconversion luminescence of Yb/Er codoped NaYF4 nanocrystals was investigated at different temperatures from 295 to 10 K. The temperature dependent luminescence intensity of the nanocrystals showed very different behaviors as compared to their bulk powders. The intensity of the green emissions initially increased and then decreased as the measurement temperature was decreased. The experimental data were explained in terms of enhanced relaxation processes in the doped nanocrystals, which may need to be taken into account in many potential applications such as thermal sensing and biosensors. [ABSTRACT FROM AUTHOR]

A full diffusion kinetic Monte Carlo algorithm is used to model nanocrystalline film deposition, and study the mechanisms of grain nucleation and microstructure formation in such films. The major finding of this work is that new grain nucleation occurs predominantly on surface peaks. Consequently, development of a nanocrystalline structure is promoted by a growth surface with nanoscale roughness, on which new grains can nucleate and grow separately from one another. The grain minor dimension (in the plane of the film) is primarily dictated by surface peak spacing, which in turn is reduced at low temperatures and high deposition rates. The grain major dimension (in the growth direction) is related to the probability of nucleating new grains on top of pre-existing ones, with finer grains being formed at low temperatures and low grain boundary energies. Because vacancies kinetically pin grain boundaries, high vacancy content, which is obtained at high deposition rate, also favors nanograins. Consistent with empirical observations common in the experimental literature, it is found that as grains shrink, they transition from elongated to equiaxed. [ABSTRACT FROM AUTHOR]

Pulse-electroplated copper that contains a high density of {111}/<112> nanotwins has been found to greatly improve the yield strength while maintaining good electrical conductivity. The thermal stability of nanotwins is a concern and has been studied by in situ transmission electron microscopy (TEM) characterization from 200 to 350 °C in the present work. It was found that the (112) twin boundary in a junction of (111)/(112)/(111) twins migrates to eliminate the (111) twin boundaries. We propose that it is the dominant mechanism that reduces the twin density in the range of temperature studied. The driving force is provided by the elimination of the two (111) boundaries. The inverse migration of the (112) twin boundary driven by a high strain is possible if enough stress has been applied to the copper, e.g., the strain introduced during pulsed electroplating. On the other hand, the migration of (111) twin boundary in the direction normal to the twin plane was not found. However, we propose that it can happen if a (112) step migrates on the (111) surface, provided that there exists a driving force. The structure and mobility of (112) twin boundary has been characterized by high resolution TEM. We observed that the (112) step on (111) twin plane has a height of three atomic layers. It is a unique structure unit of the (112) twin. [ABSTRACT FROM AUTHOR]

In this study, we have investigated the carrier transport mechanism across silicon nanocrystals with the Al/p-Si/Si nanocrystals/Al structure. Sizes of silicon nanocrystals were controlled at diameters of ∼6, ∼8, and ∼11 nm. It is shown that the conductivity σ of silicon nanocrystals, both as-grown and annealed, exhibits σ∝exp[-(T0/T)]1/2 behavior under low electrical fields and over a wide temperature range. The phenomenon of material constant T0 increasing with the decrease of nanocrystal size has been observed. Considering nanocrystal size effect, experimental results can be explained by the hopping-percolation model. The influence of nanocrystal size on transport properties has been discussed. Based on this model, changes in T0 after annealing treatment are attributed to an increase in effective decay length. [ABSTRACT FROM AUTHOR]

Thin film nanocrystalline porous silicon layers have been fabricated from amorphous silicon films using dc plasma hydrogenation and subsequent annealing at temperatures about 450 °C on silicon substrates. Plasma power densities about 5.5 W/cm2 were found to be suitable for etching of the silicon film and the creation of nanoporous layers. The nanoporous structures show visible luminescence at room temperature as confirmed by photoluminescence spectroscopy. The effects of plasma power and annealing temperature on the grain size and luminescence properties of these layers have been investigated by scanning electron microscopy, transmission electron microscopy, photoluminescence, and cathodoluminescence. It was observed that by lowering the temperature during the hydrogenation step, the diameter of the grains increased, whereas lowering the plasma power density caused the distribution of the porous surface structures to become less widely distributed and the formation of more packed structures. In addition, infrared spectroscopy has been used to investigate the origin of the light emitting behavior. [ABSTRACT FROM AUTHOR]

The orientation dependence of thin-crystal lattice fringes can be gracefully quantified using fringe-visibility maps, a direct-space analog of Kikuchi maps [Nishikawa and Kikuchi, Nature (London) 121, 1019 (1928)]. As in navigation of reciprocal space with the aid of Kikuchi lines, fringe-visibility maps facilitate acquisition of crystallographic information from lattice images. In particular, these maps can help researchers to determine the three-dimensional lattice of individual nanocrystals, to “fringe-fingerprint” collections of randomly oriented particles, and to measure local specimen thickness with only a modest tilt. Since the number of fringes in an image increases with maximum spatial-frequency squared, these strategies (with help from more precise goniometers) will be more useful as aberration correction moves resolutions into the subangstrom range. [ABSTRACT FROM AUTHOR]

We use Ar-ion milling to thin Bi2Sr2CaCu2O8+x (Bi2212) single crystals down to a few nanometers or one to two (CuO2)2 layers. In decreasing the thickness, the superconducting transition temperature gradually decreases to zero and the in-plane resistivity increases to large values indicating the existence of a superconductor-insulator transition in ultrathin Bi2212 single crystals. [ABSTRACT FROM AUTHOR]

Type III silica samples were implanted sequentially with Ti and Ag ions. The implantation of Ti results in the modification of the silica forming a Ti silicate phase. Subsequent implantation of Ag into this layer results in the formation of Ag metal nanocrystals with modified optical properties compared to samples without the Ti ions. The presence of the Ti results in significantly smaller particle size compared to samples implanted with Ag alone. The incorporation of the Ti causes a shift in the wavelength of the surface-plasmon resonance of the Ag nanocrystals and a change in the magnitude of the surface-plasmon resonance absorption. [ABSTRACT FROM AUTHOR]

Nanocrystalline, p-type semiconducting, transparent CuAlO2 thin films were deposited by direct current sputtering of a prefabricated polycrystalline CuAlO2 target, with deposition time as a variable parameter. Transmission electron micrographs reveal the formation of CuAlO2 nanoparticles. For the films deposited in 3, 9, and 15 min, the average particle sizes are determined to be around 10, 20, and 30 nm, respectively. The interplaner spacings calculated from selected area electron-diffraction patterns obtained from transmission electron microscopy confirmed the proper phase formation of the material. X-ray diffraction measurements of the films deposited for 15 and 45 min show some diffraction peaks, which depict the rhombohedral crystal structure of the material. The band-gap values obtained from the optical transmission and reflection data, for the films deposited in 3 and 9 min, are 3.94 and 3.84 eV, respectively, whereas for those films deposited in 15 and 45 min, the band-gap values lie in the range of 3.72–3.60 eV. These values are quite larger than that of bulk material, which is around 3.34 eV. The particle sizes in these cases are, respectively, 30 and 60 nm. It is well known that quantum confinement in semiconductor nanocrystals leads to the band-gap widening with respect to the bulk material. In this report we have observed an increase in the band gap of the nanostructured p-type semiconducting CuAlO2 thin film with the decrease in the particle size. Room-temperature photoluminescence measurements of this material are reported, which showed an ultraviolet near-band-edge emission around 3.60 eV, which originates from the generation and recombination of electron-hole pairs, namely, excitons. From the semiquantitative arguments it is supposed that the natural layered structure of delafossite CuAlO2 is responsible for the stability of the excitons. Also a blueshift of the emission peaks is observed with a decrease in the particle size, which may be described as another experimental indication of the quantum confinement effect within our nanocrystalline CuAlO2 thin films. The p-type nature of the films was established by hot-probe and thermopower measurements. [ABSTRACT FROM AUTHOR]

Described herein is the incorporation of nanocrystalline silicon nc-Si from porous silicon (PSi) in a silica matrix fabricated by the sol-gel technique that yields highly photoluminescent (PL) and optically transparent monoliths with uniformly distributed nc-Si inclusions or nanoclusters. The sample monoliths were prepared with PSi-derived nanoclusters (PSi-n) with average diameters of 14–45 nm. Concentrated samples of PSi-n-exhibited blueshifted orange emission bands with maximum peaks between 600 and 750 nm with PL emission intensities ten times stronger than those of the original PSi, while diluted samples exhibited UV to blue (350–450 nm) emission bands. The PL quantum yield of the typical PSi-n monoliths was 44% higher than the native PSi. Light absorption measurements showed a linear response to laser powers before the saturation threshold at 80 mW. PL bleaching following 3 h of constant laser power exposure resulted in 90% reduction of the maximum initial PL. Mechanical and thermal stability properties of nc-Si were greatly improved within the silica matrix, demonstrating that PSi-n monoliths’ are more manageable materials that enable the fabrication of samples with high densities of nc-Si for semiconducting and optoelectronic purposes. No special chemical passivation of the nc-Si surfaces was used in the preparation of the PSi-n monoliths. A strong relation between the optical properties of this nanophase material and the size distribution and concentration of nc-Si in the sample is demonstrated. [ABSTRACT FROM AUTHOR]

Rhodopsins are light-sensitive membrane proteins enabling transmembrane charge separation (proton pump) on absorption of a light quantum. Bacteriorhodopsin (BR) is a transmembrane protein from halophilic bacteria that belongs to the rhodopsin family. Potential applications of BR are considered so promising that the number of studies devoted to the use of BR itself, its mutant variants, as well as hybrid materials containing BR, in various areas grows steadily. Formation of hybrid structures combining BR with nanoparticles is an essential step in promotion of BR-based devices. However, rapid progress, continuous emergence of new data, as well as challenges of analyzing the entire data require regular reviews of the achievements in this area. This review is devoted to the issues of formation of materials based on hybrids of BR with fluorescent semiconductor nanocrystals (quantum dots) and with noble metal (silver, gold) plasmonic nanoparticles. Recent data on formation of thin (mono-) and thick (multi-) layers from materials containing BR and BR/nanoparticle hybrids are presented. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals (NCs) heavily doped with cation/anion vacancies or foreign metal ions can support localized surface plasmon resonance (LSPR) in the near-infrared (NIR) and mid-infrared (MIR) spectral wavelengths. Typically, nonstoichiometric copper sulfide Cu2−xS NCs with different x values (0 < x ≤ 1) have attracted numerous attention because of hole-based, particle size, morphology, hole density and crystal phase-dependent LSPR. In spite of excited development of methodology for LSPR manipulation, systematic LSPR tuning of Cu2−xS NCs with a special crystal phase has been limited. Herein, roxbyite Cu1.8S nanodisks (NDs) were selected as a model and their LSPR was readily tuned by particle size, hole density via chemical oxidation and reduction, self-assembly and disassembly in solution and plasmon coupling in multilayer films. Particle size, hole density and plasmon coupling severely affect their LSPR peak position and absorption intensity. Therefore, the ability of flexible LSPR tuning gifts roxbyite Cu1.8S NDs great potential in plasmonic applications, including photocatalysis, photothermal agent, two-photon photochemistry and many others in NIR and MIR regions. [ABSTRACT FROM AUTHOR]

A fluorescent nanosensor based on colloidal quantum dots CdSe/ZnS modified with mercaptoacetic acid to determine reduced glutathione, a non-protein compound that plays an important role in protection against oxidative stress, is developed. Sample preparation protocols that allow determination of reduced glutathione in a wide range of concentrations are presented. Dependence of the fluorescence intensity of the system on the incubation time for a number of concentrations of reduced glutathione was measured. The possibility of using the proposed nanosensor for reliable and sensitive determination of reduced glutathione in the concentration range from 10 to 1000 μM is confirmed. The results can be used for quantitative determination of reduced glutathione in physiological media, which is of considerable interest for medical diagnostics. [ABSTRACT FROM AUTHOR]

A dimerlike-positional-correlation heterostructure is used in one-dimensional photonic crystals to introduce the defect mode with perfect transmittance. The switching behavior of the transmittance, at the defect mode, is demonstrated theoretically. When the normal incident beam is tilted at a negligibly small angle, the perfect transmittance peak vanishes. It is found that this condition causing this phenomenon can be easily met and controlled through elucidation on the mechanism. This finding is significant for potential applications in high-precision filters and optical switches. [ABSTRACT FROM AUTHOR]

Abstract: The influence of short-chain dithiols used in a mixture with 1-dodecanethiol to build up ZnS shells, on the spectral and luminescent properties of colloidal InP@ZnS quantum dots in the course of their liquid-phase colloidal synthesis has been studied. It has been shown that the use of dithiols permits targeted control of the luminescent properties of colloidal quantum dots. In this case, nanoparticles with a narrow emission band of ≈50 nm and a luminescence quantum yield up to 0.95 can be synthesized. The results obtained extend the capabilities of using InP@ZnS colloidal quantum dots in various functional materials. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate that conductive atomic force microscopy (C-AFM) is a very powerful tool to investigate, at the nanoscale, metal-oxide-semiconductor structures with silicon nanocrystals (Si-nc) embedded in the gate oxide as memory devices. The high lateral resolution of this technique allows us to study extremely small areas (∼300 nm2) and, therefore, the electrical properties of a reduced number of Si-nc. C-AFM experiments have demonstrated that Si-nc enhance the gate oxide electrical conduction due to trap-assisted tunneling. On the other hand, Si-nc can act as trapping centers. The amount of charge stored in Si-nc has been estimated through the change induced in the barrier height measured from the I-V characteristics. The results show that only ∼20% of the Si-nc are charged, demonstrating that the electrical behavior at the nanoscale is consistent with the macroscopic characterization. [ABSTRACT FROM AUTHOR]

We describe herein an operationally advantageous general methodology for efficiently activating lipoic acid based compounds, a family of popular surface ligands for semiconductor nanocrystals, through the use of a borohydride exchange resin, and the use of the activated species to replace the native surface ligands of quantum dots. The procedure enabled phase transfer of the nanocrystals between polar and aqueous media and, if unsubstituted lipoic acid was used, a facile adjustment of their solubility in a wide range of solvents with varying polarity (from hexane to water). We show that the protocol is applicable to different types of nanocrystals and a variety of lipoic acid based ligands, and that the resulting quantum dots maintain their optical properties, in particular, an intense luminescence, and long-term colloidal stability. [ABSTRACT FROM AUTHOR]

Chirality strongly influences many biological properties of materials, such as cell accumulation, enzymatic activity, and toxicity. In the past decade, it has been shown that quantum dots (QDs), fluorescent semiconductor nanoparticles with unique optical properties, can demonstrate optical activity due to chiral ligands bound on their surface. Optically active QDs could find potential applications in biomedical research, therapy, and diagnostics. Consequently, it is very important to investigate the interaction of QDs capped with chiral ligands with living cells. The aim of our study was to investigate the influence of the induced chirality of Mn-doped ZnS QDs on the viability of A549 cells. These QDs were stabilized with D- and L-cysteine using a ligand exchange technique. The optical properties of QDs were studied using UV-Vis, photoluminescence (PL), and circular dichroism (CD) spectroscopy. The cytotoxicity of QDs was investigated by high content screening analysis. It was found that QDs stabilized by opposite ligand enantiomers, had identical PL and UV-Vis spectra and mirror-imaged CD spectra, but displayed different cytotoxicity: QDs capped with D-cysteine had greater cytotoxicity than L-cysteine capped QDs. [ABSTRACT FROM AUTHOR]

We report on the first Au-catalyzed growth of CdTe nanowires by metalorganic vapor phase epitaxy. The nanowires were obtained by a separate precursors flow process in which (i) di-isopropyl-telluride (iPr2Te) was first flowed through the reactor to ensure the formation of liquid Au–Te alloy droplets, and (ii) after purging with pure H2 to remove unreacted iPr2Te molecules from the vapor and the growth surface, (iii) dimethylcadmium (Me2Cd) was supplied to the vapor so that Cd atoms could enter the catalyst droplets, leading to nanowire self-assembly. CdTe nanowires were grown between 485 and 515 °C on (111)-B-GaAs substrates, the latter preliminary deposited with a 2 μm thick (111)-oriented CdTe buffer layer onto which Au nanoparticles were provided. As-grown CdTe nanowires were vertical ([111]-aligned) straight segments of constant diameter and showed an Au-rich nanodroplet at their tips, the contact angle between the droplets and the nanowires being ∼130°. The nanowire axial growth rate appeared kinetics-limited with an activation energy ∼57 kcal/mol. However, the growth rate turned independent from the nanowire diameter. Present data are interpreted by a theoretical model explaining the nanowire growth through the diffusion transport of Te adatoms under the assumption that their growth occurs during the Me2Cd-flow process step. Low-temperature cathodoluminescence spectra recorded from single nanowires showed a well-resolved band-edge emission typical of zincblend CdTe along with a dominant band peaked at 1.539 eV. [ABSTRACT FROM AUTHOR]

The realization of both high efficiency and strong bending-durability is a critical issue for future applications of colloidal quantum dot solar cells (CQDSCs) in flexible devices. Herein, we fabricated flexible CQDSCs with a three-dimensional electron transport layer (ETL) composed of a ZnO nanowire (NW) array for efficient carrier collection and probed the effect of the NW array on the bendability of flexible cells. The good bendability of cells with ZnO NWs was verified from the consistency of photovoltaic performance during mechanical bending treatment with various bending angles and cycles. The efficient release of stress inside the three-dimensional CQDSCs with the ZnO NW array led to the maintenance of 97% of the initial power conversion efficiency at a bending angle of 160°. In contrast, crack formation on the common planar ETL of CQDSCs formed by ZnO nanoparticles resulted in a degradation of device performance to 77% of the initial one at the same angle. Our research demonstrated that the bending stability of the ZnO NW array may be promising for commercial applications of flexible photovoltaic devices. [ABSTRACT FROM AUTHOR]

In the present work, we studied the photon down-conversion effect produced by thin films of silicon oxide with embedded silicon nanocrystals also called silicon-rich oxide (SRO). These films have been used to absorb high energy light and the re-emission of two or more low energy photons (~1.1 eV) with the goal of improving the external quantum efficiency and consequently the conversion efficiency of silicon solar cells. According to our results, the incorporation of a thin SRO film on the solar cell surface increases the short circuit current and the FF of the silicon solar cells; the enhancement of spectral response is due to the high photoluminescence intensity of the SRO in the visible region when irradiated with UV light. An improvement of 38% in the solar cell efficiency has been observed in our particular solar cell fabrication process by the use of an SRO film with high photoluminescence intensity, which replaces the conventional silicon dioxide film. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A PbSe quantum dot solar cell with an efficiency of 7.22% and a fill factor of 62.4% is achieved by applying a CsPbBr3 perovskite quantum dot back layer. The back layer can effectively suppress carrier recombination at the PbSe/Au interfaces, hence lead to significant improvement in open‐circuit voltage and fill factor. [ABSTRACT FROM AUTHOR]

CdS, CdTe, ZnO, and ZnO:Co nanocrystals and related hybrid nanostructures, in which the nanoparticles combined with graphene, have been studied. Different chemical approaches for synthesis of II-VI semiconductor nanocrystal-graphene hybrids have been applied depending on chemical composition. Transmission electron microscopy characterizations proved the formation of graphene based hybrid nanostructures. Absorption spectra near band-gap edge have shown changes due to the interaction of the nanocrystals with graphene. The revealed photoluminescence quenching effect in II-VI semiconductor nanocrystal-graphene hybrids can be served as evidence for electron transfer from the nanoparticles to graphene. Results of Faraday rotation measurements in doped ZnO:Co nanocrystals and their hybrids at room temperature demonstrated paramagnetic behaviour for both kinds of samples. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Pluronic (P123) capped lead sulphide (PbS) nanoparticles were synthesized for the first time by simple wet chemical method. Series of experiments were conducted by changing the concentration of P123 to establish the most suitable conditions for obtaining different morphologies of PbS nanoparticles. The synthesized product has been characterized by powder X-ray diffraction (XRD), UV-Vis spectrophotometry, scanning electron microscopy (SEM), transmission electron Microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and photoluminescence studies. The particle size observed from XRD analysis is around 44-3 nm. Significant 'blue shift' from bulk material was observed on the PbS nanoparticles using UV-Vis spectra. A sevenfold increase in photoluminescence intensity has been observed from PbS nanoparticles after surface passivation by P123 agent. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs), namely semiconductor nanocrystals, due to their particular optical and electronic properties, have growing applications in device technology, biotechnology and biomedical fields. Nevertheless, the possible threat to human health and the environment have attracted increasing attention as the production and applications of QDs increases rapidly while standard evaluation of safety lags. In the present study we performed proteomic analyses, by means of 2D gel electrophoresis and Surface Enhanced Laser Desorption Ionization-Time of Flight-Mass Spectrometry (SELDI-TOF-MS). We aimed to identify potential biomarkers of exposure to CdSe/ZnS quantum dots. The marine diatom Phaeodactylum tricornutum exposed to 2.5 nM QDs was used as a model system. Both 2DE and SELDI showed the presence of differentially expressed proteins. By Principal Component Analysis (PCA) we were able to show that the differentially expressed proteins can discriminate between exposed and not exposed cells. Furthermore, a protein profile specific for exposed cells was obtained by SELDI analysis. To our knowledge, this is the first example of the application of SELDI technology to the analysis of microorganisms used as biological sentinel model of marine environmental pollution. [ABSTRACT FROM AUTHOR]

Group IV (Ge and Si) nanocrystals embedded in a dielectric matrix were prepared via rf magnetron sputtering by the deposition of superlattices of stoichiometric and substoichiometric oxide layers and subsequent annealing. By this way Ge nanocrystals in a (Ta)ZrO x and Si nanocrystals in an SiO2 matrix were prepared in a size and shape controlled manner. In case of the Ge-ZrO2 system, elongated Ge nanocrystals in a crystallized ZrO2 matrix were formed for annealing temperatures above 660 °C. Starting from a Si3N4 interface of the Si wafer, a preferential orientation between the Ge and ZrO2 lattice can be stated. Doping the ZrO2 matrix additionally with Ta increases the crystallization temperature of the ZrO2 matrix and leads to the formation of Ge nanocrystals embedded in an amorphous TaZrO x matrix. The Ge nanocrystals were investigated by photoluminescence measurements and implemented into metal-insulator-semiconductor capacitor to investigate their potential for charge trapping devices. The prepared nano floating gate devices show good charging characteristics with a maximum memory window of 5 V and a slope of the writing voltage vs. memory window characteristics of 0.8-1. All luminescence centers seen in the Ge-(Ta)ZrO x system can be attributed to defects either from the Ge nanocrystal surface, the (Ta)ZrO x matrix or the Si substrate itself. Si nanocrystals were fabricated in the same way in an amorphous SiO2 film after annealing above 900 °C. The formed Si nanocrystals act as superior sensitizer for Er3+ ions which were ion implanted into the films followed by an additional subsequent anneal, varied between 700 and 1000 °C. The Si nanocrystal - Er3+ system was successfully implemented into a slot waveguide structure showing a strong polarization dependent field enhancement in both emission and excitation geometry. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Polyoxometalate (POM) cluster anions are shown to serve as covalently coordinated ligands for anatase-TiO2 nanocrystals, giving isolable assemblies uniquely positioned between molecular macroanions and traditional colloidal nanoparticles. Na+ salts of the water-soluble polyanionic structures are obtained by reacting amorphous TiO2 with the 1 nm lacunary ion, Na7[α-XW11O39] (X=P5+), at 170 °C, after which an average of 55 α-PW11O397− clusters are found as pentadentate ligands for TiIV ions covalently linked to 6 nm single-crystal anatase cores. The attached POMs are reversible electron acceptors, the reduction potentials of which shift in a predictable fashion by changing the central heteroatom, X, directly influencing a model catalytic reaction. Just as POM cluster anions control the reactivities of metal centers in molecular complexes, directly coordinated POM ligands with tunable redox potentials now provide new options for rationally controlling the reactions of semiconductor nanocrystals. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) have attracted significant interest for applications in electronic and optoelectronic devices such as photodetectors, light emitting diodes, and solar cells. However, a poor understanding of charge transport in these nanocrystalline films hinders their practical applications. The photocarrier radiometry (PCR) technique, a frequency-domain photoluminescence method spectrally gated for radiative recombination photon emissions and exclusion of thermal infrared photons, has been applied to a coupled PbS CQD thin film with inter-dot spacing of 0.5 nm to 1 nm for the analysis of charge transport properties. As the nanoparticle bandgap depends on the size of the quantum dots, polydispersity of the CQD thin film causes bandgap variability leading to photoexcited carrier (exciton) decay lifetime broadening and temperature dependence. The carrier transport mechanisms of QDs are quite different from bulk semiconductors, so the conventional carrier-diffusion wave-based PCR theory was modified into a non-diffusive limit model. A developed variational discrete lifetime reconstruction approach was used to analyze PCR frequency scans under two optical excitation modes: a modulated laser source without, and with, an additional continuous laser source. Using this model, the CQD mean lifetime values were found and variational discrete lifetime spectra were reconstructed. [ABSTRACT FROM AUTHOR]