Showing papers on "Potential well published in 2014"
TL;DR: In this article, a fusion of aromatic motifs into conjugated carbon nitride nanosheets has been developed, which results in a redshift of the optical absorption and an improved charge separation in the polymer semiconductor.
Abstract: To counteract the unwanted quantum confinement effect and less efficient electron screening in low dimensional carbon nitride, fusion of aromatic motifs into conjugated carbon nitride nanosheets has been developed. This results in a red-shift of the optical absorption and an improved charge separation in the polymer semiconductor, establishing a quantum efficiency of 8.8% at 420 nm for H2 generation.
307 citations
TL;DR: In this article, the authors showed that the significantly different photocatalytic activity of the quantum sized BiVO4 arises from the negative shift of conduction band edge by a quantum confinement effect and a decreased overpotential for water reduction.
Abstract: Photocatalytic water splitting is the most promising process to convert solar energy into high purity chemical fuel (hydrogen), which has received significant attention in recent years. Only several photocatalysts have been reported in the literature for pure water splitting under visible light. Herein we report for the first time quantum sized BiVO4 can decompose pure water into H2 and O2 simultaneously under simulated solar light irradiation without any cocatalysts or sacrificial reagents. By electrochemical measurement, we demonstrate that the significantly different photocatalytic activity of the quantum sized BiVO4 arises from the negative shift of conduction band edge by a quantum confinement effect and a decreased overpotential for water reduction. Although the generated H2 and O2 are nonstoichiometric in the present study, these findings establish the great potential of using quantum sized BiVO4 photocatalyst and solar energy for overall water splitting.
247 citations
TL;DR: In this article, the size-dependent excited state optical properties of Ag2S QDs are systematically investigated by photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy.
Abstract: Ag2S quantum dots (QDs) have attracted increasing attention due to their appealing optical properties in the near-infrared regime. However, a full understanding of the quantum confinement effect of Ag2S QDs has not been achieved so far. Herein, for the first time, the size-dependent excited state optical properties of Ag2S QDs are systematically investigated by photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy. Experimentally, we determine the exciton Bohr radius of Ag2S QDs as 2.2 nm, which is highly consistent with theoretical results.
191 citations
TL;DR: The structural properties of synthesized ZnO nanoparticles have been confirmed using the TEM micrographs as discussed by the authors, which shows that the hexagonal (a = 3.2459 A, c = 5.1999 A) structure is the predominant crystallographic structure and the average size of the nanoparticles is 22.4 ± 0.6 nm.
Abstract: ZnO nanoparticles are prepared through hydrolysis and condensation of zinc acetate dihydrate by potassium hydroxide in alcoholic medium at low temperatures. Thermal gravimetric analysis (TGA) of the precursor is made in order to specify the temperature range over which the weight loss and thermal effect are significant. X-ray diffraction of the as-prepared specimens shows that the hexagonal (a = 3.2459 A, c = 5.1999 A) structure is the predominant crystallographic structure. According to Scherer's formula, the average size of the nanoparticles is 22.4 ± 0.6 nm. The structural properties of the synthesized ZnO nanoparticles have been confirmed using the TEM micrographs. The optical energy gap of the ZnO nanoparticles, as obtained from applying Tauc's equation, is equal to 3.52 eV, which is higher than that of the bulk material. Absorption peak of the as-prepared sample is 298nm which is highly blue shifted as compared to the bulk (360 nm). Large optical energy gap and highly blue shifted absorption edge confirm that the prepared ZnO nanoparticle exhibits strong quantum confinement effect.
111 citations
TL;DR: This work has been performed to determine the critical size of the GeO2 nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance.
Abstract: This work has been performed to determine the critical size of the GeO2 nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance. GeO2 nanoparticles with different sizes of ∼2, ∼6, ∼10, and ∼35 nm were prepared by adjusting the reaction rate, controlling the reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO2 nanoparticles, the ∼6 nm sized GeO2 showed the best electrochemical performance. Unexpectedly smaller particles of the ∼2 nm sized GeO2 showed the inferior electrochemical performances compared to those of the ∼6 nm sized one. This was due to the low electrical conductivity of the ∼2 nm sized GeO2 caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. Those characteristics of the smaller nanoparticles led to poor electrochemical performances, and their relationships were discussed.
103 citations
TL;DR: The role of surface and deep-level defects on the blue emission of tin oxide quantum dots (SnO₂ QDs) synthesized by the solution-combustion method at different combustion temperatures is reported.
Abstract: This paper reports on the role of surface and deep-level defects on the blue emission of tin oxide quantum dots (SnO2 QDs) synthesized by the solution-combustion method at different combustion temperatures. X-ray diffraction studies showed the formation of a single rutile SnO2 phase with a tetragonal lattice structure. High resolution transmission electron microscopy studies revealed an increase in the average dot size from 2.2 to 3.6 nm with an increase of the combustion temperature from 350 to 550 °C. A decrease in the band gap value from 3.37 to 2.76 eV was observed with the increase in dot size due to the quantum confinement effect. The photoluminescence emission was measured for excitation at 325 nm and it showed a broad blue emission band for all the combustion temperatures studied. This was due to the creation of various oxygen and tin vacancies/defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the blue emission in the SnO2 QDs is discussed with the help of an energy band diagram.
97 citations
TL;DR: This work shows that cubic phase silicon carbide nanoparticles with diameters in the range 45-500 nm can host other point defects responsible for photoinduced intrabandgap PL, and demonstrates that these nanoparticles exhibit single photon emission at room temperature with record saturation count rates.
Abstract: The photoluminescence (PL) arising from silicon carbide nanoparticles has so far been associated with the quantum confinement effect or to radiative transitions between electronically active surface states. In this work we show that cubic phase silicon carbide nanoparticles with diameters in the range 45-500 nm can host other point defects responsible for photoinduced intrabandgap PL. We demonstrate that these nanoparticles exhibit single photon emission at room temperature with record saturation count rates of 7 × 10(6) counts/s. The realization of nonclassical emission from SiC nanoparticles extends their potential use from fluorescence biomarker beads to optically active quantum elements for next generation quantum sensing and nanophotonics. The single photon emission is related to single isolated SiC defects that give rise to states within the bandgap.
94 citations
TL;DR: In this article, a facile one-step method for the preparation of ZnO-ZnS core-shell type-II nanostructures, pure ZnS quantum dots and pure znO nanoparticles with different experimental conditions is demonstrated.
76 citations
TL;DR: In this article, structural, spectroscopic and crystal field studies of ZnS nanoparticles, both pure and doped with Mn2+ ions, successfully synthesized at room temperature using a simple reverse micelle technique in the Triton X-100/cyclohexane medium.
63 citations
TL;DR: The role of quantum dots (QDs) of SnO2 in detecting low concentrations of methane (CH4) at a relatively low temperature of ∼150 °C with high response (S ∼ 3.5%) and response time below 1 min is reported.
Abstract: The role of quantum dots (QDs) of SnO2 in detecting low concentrations of methane (CH4) at a relatively low temperature of ∼150 °C with high response (S ∼ 3.5%) and response time below 1 min is reported. A simple room temperature single step chemical process was adopted for the growth of SnO2 nanoparticles of a size around 2.4 nm. These nanoparticles were subsequently annealed at 800 °C to increase the grain size to 25 nm. The as-prepared SnO2 nanoparticles, being smaller than the corresponding Bohr radius (2.7 nm), showed a strong quantum confinement effect with a blue shift in the band gap energy from 3.6 eV for the bulk SnO2 to 4.37 eV for the QDs. These QDs exhibited a strong sensing response to CH4 in comparison to the annealed sample. A low activation energy of 90 meV, as estimated from the temperature dependent S plot for SnO2 QDs, was found to be the driving force for such unusual high sensitivity at a low operating temperature. X-ray diffraction, transmission electron microscopy, along with Raman spectroscopy measurements are used for the detailed structural studies. The critical role of the chemisorbed oxygen species present at different operating temperatures on the surface of the off-stoichiometric quantum sized SnO2 and bulk-like annealed samples are discussed in light of the adsorption kinetics.
62 citations
TL;DR: In this article, a vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbing and electron accepting roles for (Cl) GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ∼105 at room temperature using a 405nm laser irradiation under the reverse bias voltage.
Abstract: Graphene quantum dots (GQDs) are becoming one of the hottest advanced functional materials because of the opening of the bandgap due to quantum confinement effect, which shows unique optical and electrical properties. The chlorine doped GQDs (Cl-GQDs) have been fabricated by chemical exfoliation of HCl treated carbon fibers (CFs), which were prepared from degreasing cotton through an annealing process at 1000 °C for 30 min. Raman study shows that both G and 2D peaks of GQDs may be redshifted (softened) by chlorine doping, leading to an n-type doping. The first vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbing and electron-accepting roles for (Cl)-GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ∼105 at room temperature using a 405 nm laser irradiation under the reverse bias voltage. The study expands the application of (Cl)-GQDs to the important optoelectronic detection devices.
TL;DR: In this paper, an all-optical modulation based on silicon quantum dot doped SiOx:Si-QD waveguide is demonstrated, where the free-carrier absorption (FCA) cross section of Si-QDs is decreased to 8 × 10−18 cm2 by enlarging the electron/hole effective masses, which shortens the PL and Auger lifetime.
Abstract: All-optical modulation based on silicon quantum dot doped SiOx:Si-QD waveguide is demonstrated. By shrinking the Si-QD size from 4.3 nm to 1.7 nm in SiOx matrix (SiOx:Si-QD) waveguide, the free-carrier absorption (FCA) cross section of the Si-QD is decreased to 8 × 10−18 cm2 by enlarging the electron/hole effective masses, which shortens the PL and Auger lifetime to 83 ns and 16.5 ps, respectively. The FCA loss is conversely increased from 0.03 cm−1 to 1.5 cm−1 with the Si-QD size enlarged from 1.7 nm to 4.3 nm due to the enhanced FCA cross section and the increased free-carrier density in large Si-QDs. Both the FCA and free-carrier relaxation processes of Si-QDs are shortened as the radiative recombination rate is enlarged by electron–hole momentum overlapping under strong quantum confinement effect. The all-optical return-to-zero on-off keying (RZ-OOK) modulation is performed by using the SiOx:Si-QD waveguides, providing the transmission bit rate of the inversed RZ-OOK data stream conversion from 0.2 to 2 Mbit/s by shrinking the Si-QD size from 4.3 to 1.7 nm.
TL;DR: The effect of rod morphology should be carefully considered in designing multicomponent nanorods for solar energy conversion applications because of the possibilities of using the band alignment of component materials and the rod-diameter-dependent quantum confinement effect to control the location of electrons and holes.
Abstract: One-dimensional colloidal multicomponent semiconductor nanorods, such as CdSe–CdS dot-in-rod, have been extensively studied as a promising class of new materials for solar energy conversion because of the possibilities of using the band alignment of component materials and the rod-diameter-dependent quantum confinement effect to control the location of electrons and holes and to incorporate catalysts through the growth of Pt tips. Here we used CdS nanorods as an example to study the effect of nonuniform diameters along the rod on the exciton localization and dissociation dynamics in CdS and (platinum tipped) CdS–Pt nanorods. We showed that, in CdS nanorods prepared by seeded growth, the presence of a bulb with a larger diameter around the CdS seed resulted in an additional absorption band lower in energy than the exciton in the CdS rod. As a result, excitons generated in the CdS rod could undergo ultrafast localization to the bulb region in addition to trapping on the CdS rod. We observed that the Pt tip ...
TL;DR: An ultrathin layer of ZnO between 3 and 6 nm, which exhibits quantum confinement effect, is found to be sufficient to transport the photogenerated electrons to the external contacts and exhibits near-unity collection efficiency.
Abstract: We present a photoanode for dye-sensitized solar cell (DSC) based on ZnO nanoshell deposited by atomic layer deposition at 150 °C on a mesoporous insulating template. An ultrathin layer of ZnO between 3 and 6 nm, which exhibits quantum confinement effect, is found to be sufficient to transport the photogenerated electrons to the external contacts and exhibits near-unity collection efficiency. A 6 nm ZnO nanoshell on a 2.5 μm mesoporous nanoparticle Al2O3 template yields photovoltaic power conversion efficiency (PCE) of 4.2% in liquid DSC. Perovskite absorber (CH3NH3PbI3) based solid state solar cells made with similar ZnO nanostructures lead to a high PCE of 7%.
TL;DR: In this paper, Sb2O3 quantum dots (QDs) anchored graphene composites were prepared by in situ chemical route, followed by the subsequent annealing, and the resulting samples were characterized by X-ray diffraction and electron microscopy for structural and morphological analysis.
TL;DR: It is noteworthy that the present glass nanosystem as a photocatalyst was found to be very stable as compared to naked powder photocatalysts, and a study of size tuneable photoc atalytic activity for hydrogen generation from hydrogen sulfide splitting was performed under visible light irradiation for the first time.
Abstract: We have demonstrated unique CdS0.5Se0.5 and CdSe quantum dot–glass nanosystems with quantum confinement effect. The stable, monodispersed CdS0.5Se0.5 and CdSe quantum dots (QDs) of size 2 to 12 nm have been grown in a germanate glass matrix by a simple melt quench technique at moderate temperature. XRD and Raman studies show formation of hexagonal CdS0.5Se0.5 and CdSe in the glass matrix. The quantum confinement of CdS0.5Se0.5 and CdSe was studied using TEM and UV-Vis spectroscopy. The band gap of the glass nanosystem was tuned from 3.6 to 1.8 eV by controlling the CdS0.5Se0.5 quantum dot size in the glass matrix. It can be further tuned to 1.68 eV using growth of CdSe quantum dots in the glass matrix. Considering the tuneable band gap of the CdS0.5Se0.5 and CdSe quantum dot–glass nanosystem for the visible light absorption, a study of size tuneable photocatalytic activity for hydrogen generation from hydrogen sulfide splitting was performed under visible light irradiation for the first time. The utmost hydrogen evolution, i.e. 8164.53 and 7257.36 μmol h−1 g−1 was obtained for the CdS0.5Se0.5 and CdSe quantum dot–glass nanosystems, respectively. The apparent quantum yield (AQY) was observed to be 26% and 21% for the CdS0.5Se0.5 and CdSe quantum dot–glass nanosystems, respectively. It is noteworthy that the present glass nanosystem as a photocatalyst was found to be very stable as compared to naked powder photocatalysts.
TL;DR: In this article, the CdTe QDs powder and the as-deposition films were characterized using X-ray diffraction and high resolution transmission electron microscope (HRTEM).
TL;DR: In this article, the characterization of sol-gel derived MgZnO thin films annealed by atmospheric pressure plasma jets (APPJs) is presented. But the results are limited to the case when the material is amorphous/nanocrystalline.
TL;DR: In this article, a single-step synthesis of stable, luminescent aqueous colloids of mercaptopropionic acid capped cadmium selenide nanoparticles of controllable size was reported.
TL;DR: In this paper, the dielectric function, band gap, and exciton binding energies of ultrathin ZnO films as a function of film thickness have been obtained with spectroscopic ellipsometry.
Abstract: Dielectric function, band gap, and exciton binding energies of ultrathin ZnO films as a function of film thickness have been obtained with spectroscopic ellipsometry. As the film thickness decreases, both real (e1) and imaginary (e2) parts of the dielectric function decrease significantly, and e2 shows a blue shift. The film thickness dependence of the dielectric function is shown related to the changes in the interband absorption, discrete-exciton absorption, and continuum-exciton absorption, which can be attributed to the quantum confinement effect on both the band gap and exciton binding energies.
TL;DR: In this article, extensive results in the characterization of quantum dots using the Langmuir monolayer technique to approach these quantum dots in their two dimensional state are presented, and the results show that a more condensed packing state is achieved with the use of smaller ligands.
TL;DR: In this article, the Cubic phase of ZnS was confirmed using both X-ray diffraction and high-resolution transmission electron microscopy, which revealed strong quantum confinement effect for a typical Zns of 3nm size with a band gap of 4.46 eV in comparison to the bulk value of 3.55 eV.
TL;DR: In this paper, Cadmium selenide (CdSe) quantum dots in selective size were prepared by using inverse micelle technique without the presence of trioctylphosphine (TOP) and characterized by UV-visible absorption, Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopic studies.
TL;DR: The higher-yield preparation of blue-emitting colloidal Si nanocrystals with a diameter range of 1-3 nm by selective laser ablation of porous Si powder in an organic solution, compared with theablation of bulk Si powder is demonstrated.
Abstract: We demonstrate the higher-yield (one order of magnitude) preparation of blue-emitting colloidal Si nanocrystals with a diameter range of 1–3 nm by selective laser ablation of porous Si powder in an organic solution, compared with the ablation of bulk Si powder. This increase in yield is the result of the lower thermal conductivity and the larger surface area of porous Si. The prepared colloidal Si nanocrystal exhibits size-dependent, higher-lying bandgap energies and large radiative decay rates as a result of the quantum confinement effect. Reversible luminescence color change from blue to yellow and vice versa in the colloidal Si nanocrystal film is also observed, and this is attributed to the non-radiative inter-crystal energy transfer.
TL;DR: The realization of an organic quantum well indicates the highly delocalized transport mechanism in well-defined organic crystalline systems and promises novel organic "quantum" optoelectronic devices.
Abstract: A meaningful organic quantum well based on crystalline heteroepitaxy films is constructed. The quantum confinement effect is demonstrated by its reflections on optics and electrics: the blueshift of the optical characteristic peaks and the negative differential resistance at room temperature. The realization of an organic quantum well indicates the highly delocalized transport mechanism in well-defined organic crystalline systems and promises novel organic "quantum" optoelectronic devices.
TL;DR: In this article, the first synthesis of ultrasmall CuInSe2 quantum dots (QDs) with diameters below the exciton Bohr radius 10.6 nm by a solvothermal method was reported.
Abstract: Here we report the first synthesis of ultrasmall CuInSe2 quantum dots (QDs) with diameters below the exciton Bohr radius 10.6 nm by a solvothermal method. The synthesis is conducted in oleylamine without any organometallic precursors. The quantum confinement effect has been identified in the optical absorption spectra. Through pre-loading CuInSe2 QDs on TiO2 film, a good electron transfer dynamics could be observed on the CdS/CuInSe2/TiO2 film. Under one sun of simulated irradiation, the resultant quantum dot sensitized solar cell based on CdS/CuInSe2 exhibited a power conversion efficiency of about 2.27%, which was 55% higher than that of the single CdS sensitized solar cell. It indicates that CuInSe2 QDs have great potential in photovoltaic applications.
TL;DR: In this paper, the structural, morphological and photo-physical properties and biocompatibility of ZnS semiconductor quantum dots were investigated using comprehensive characterization techniques such as x-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), dynamic light scattering (DLS), Fourier transform infrared spectrometry (FT-IR), UV-Vis optical absorption, photoluminescence (PL) spectrometer and MTT assay.
Abstract: In the present study, the ZnS semiconductor quantum dots were successfully synthesized via an aqueous method utilizing glutathione (GSH), thioglycolic acid (TGA) and polyvinyl pyrrolidone (PVP) as capping agents. The structural, morphological and photo-physical properties and biocompatibility were investigated using comprehensive characterization techniques such as x-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), dynamic light scattering (DLS), Fourier transform infrared spectrometry (FT-IR), UV-Vis optical absorption, photoluminescence (PL) spectrometer and MTT assay. The XRD patterns showed a cubic zinc blende crystal structure and a crystallite size of about 2–3 nm using Scherrer’s equation confirmed by the electron micrographs and Effective Mass Approximation (EMA). The DLS and zeta-potential results revealed that GSH capped ZnS nanoparticles have the narrowest size distribution with an average size of 27 nm and relatively good colloidal stability. Also, the FT-IR spectrum confirmed the interaction of the capping agent groups with ZnS nanoparticles. According to the UV-Vis absorption results, optical bandgap of the spherical capped nanoparticles is higher compared to the uncapped sample and could be wider than 3.67 eV (corresponding to the bulk ZnS), which is due to the quantum confinement effect. From photoluminescence spectra, it was found that the emission becomes more intensive and shifts towards the shorter wavelengths in the presence of the capping agent. Moreover, the emission mechanism of uncapped and capped ZnS was discussed in detail. Finally, the MTT results revealed the satisfactory (>94%) biocompatibility of GSH capped ZnS quantum dots which would be a promising candidate applicable in fluorescent biological labels.
TL;DR: In this article, pure and nickel doped cadmium sulphide nanoparticles at pH value 10 with three different concentrations have been synthesized by chemical precipitation method using Diethylene triamine was used as stabilizing agent to control the particle size as quantum dots without any agglomeration.
Journal Article•
TL;DR: In this paper, the structural and optical properties of the samples were investigated by X-ray diffraction and UV-VISNIR absorption spectroscopy, which revealed the wurtzite structure of ZnO.
Abstract: The synthesis of ZnO nanoparticles has attracted considerable interest because of their unique properties and potential applications in a variety of solid state devices, catalytic media etc. By using water-in-oil (w/o) microemulsions, nanodroplets of water were used as chemical reactor to synthesize nanoparticles of zinc oxide. Addition of reducing agent ((NH4)2CO3) and zinc salt (Zn(NO3)2) followed by heat treatment results in the formation of zinc oxide nanoparticles (NPs). The structural and optical properties of the samples were investigated by X-ray diffraction and UV-VISNIR absorption spectroscopy. X-ray diffraction revealed the wurtzite structure of ZnO. Percentage of lattice contraction and average particle size of the sample were also calculated from the XRD. Size-dependent blue shifts of absorption spectra revealed the quantum confinement effect. Furthermore, on increasing annealing temperature of ZnO NPs, crystallize size increases which, in turn,decreases the band gap energy and photocatalytic degradation efficiency of phenol.
TL;DR: In this article, the band-gap energy of most of the Si nanoparticles is estimated to be 2.5-3.3 eV from the PL spectra, corresponding to the Si particle size of 1.9−3.2 nm.
Abstract: Si nanoparticles are produced from Si swarf which is a waste during slicing Si ingots to produce Si wafers for solar cell use. The beads mill method produces flake-like Si with scores of nanometers width from Si swarf. Subsequent photochemical dissolution with light longer than 560 nm wavelength in a 0.5 % HF solution results in sphere-shaped Si nanoparticles of 1–7 nm diameter. Si nanoparticles dispersed in ethanol show blue photoluminescence at ~400 nm (3.1 eV) under UV irradiation, indicating band-gap widening due to the quantum confinement effect. The band-gap energy of most of the Si nanoparticles is estimated to be 2.5–3.3 eV from the PL spectra, corresponding to the Si nanoparticle size of 1.9–3.2 nm. On the other hand, Si nanoparticles produced by immersion in the HF solution in the dark show much weaker blue photoluminescence. These results demonstrate that the Si dissolution reaction is greatly enhanced by photo-generated holes.