Size Effects in ZnO: The Cluster to Quantum Dot Transition

2003 ◽  
Vol 56 (10) ◽  
pp. 1051 ◽  
Author(s):  
Annabel Wood ◽  
Michael Giersig ◽  
Michael Hilgendorff ◽  
Antonio Vilas-Campos ◽  
Luis M. Liz-Marzán ◽  
...  
Keyword(s):  
Blue Shift ◽  
X Ray Diffraction ◽  
Exciton Transition ◽  
Quantum Size ◽  
Transmission Electron ◽  
Relative Value ◽  
Excitonic Transition ◽  
Zno Colloids ◽  
Tetraalkylammonium Hydroxides ◽  
Exciton Absorption Band

The use of tetraalkylammonium hydroxides to prepare ZnO colloids with diameters ranging from 1 to 6 nm is described. The position of the first excitonic transition has been measured by UV-vis spectrometry and correlated with the particle size, which has been measured using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and ultracentrifugation (UC). The exciton transition is first visible at 265–270 nm corresponding to particle diameters around 1 nm; the exciton absorption band then becomes sharper and narrower, while the band red-shifts only slowly. Based on the sizing data from HRTEM, XRD, and UC, it is concluded that the quantum size effect at sizes less than the Bohr radius is significantly less than predicted from the Kayanuma equation. Based on the blue-shift in the trap emission as a function of nanocrystal size, the effective masses of the electron and hole (me, mh) remain constant in particles down to 1 nm in diameter, with a relative value given by me/(me+mh)=0.55 ± 0.04.

scholarly journals Controlled Synthesis of CuS and Cu9S5 and Their Application in the Photocatalytic Mineralization of Tetracycline

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 899
Author(s):  
Murendeni P. Ravele ◽  
Opeyemi A. Oyewo ◽  
Damian C. Onwudiwe
Keyword(s):  
Electron Microscopy ◽  
Visible Light ◽  
Blue Shift ◽  
X Ray Diffraction ◽  
X Ray ◽  
Copper Sulfides ◽  
Transmission Electron ◽  
Single Source Precursor ◽  
Pure Phase ◽  
Pure Phases

Pure-phase Cu2−xS (x = 1, 0.2) nanoparticles have been synthesized by the thermal decomposition of copper(II) dithiocarbamate as a single-source precursor in oleylamine as a capping agent. The compositions of the Cu2−xS nanocrystals varied from CuS (covellite) through the mixture of phases (CuS and Cu7.2S4) to Cu9S5 (digenite) by simply varying the temperature of synthesis. The crystallinity and morphology of the copper sulfides were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), which showed pure phases at low (120 °C) and high (220 °C) temperatures and a mixture of phases at intermediate temperatures (150 and 180 °C). Covellite was of a spherical morphology, while digenite was rod shaped. The optical properties of these nanocrystals were characterized by UV−vis–NIR and photoluminescence spectroscopies. Both samples had very similar absorption spectra but distinguishable fluorescence properties and exhibited a blue shift in their band gap energies compared to bulk Cu2−xS. The pure phases were used as catalysts for the photocatalytic degradation of tetracycline (TC) under visible-light irradiation. The results demonstrated that the photocatalytic activity of the digenite phase exhibited higher catalytic degradation of 98.5% compared to the covellite phase, which showed 88% degradation within the 120 min reaction time using 80 mg of the catalysts. The higher degradation efficiency achieved with the digenite phase was attributed to its higher absorption of the visible light compared to covellite.

scholarly journals New Electrospun ZnO:MoO3 Nanostructures: Preparation, Characterization and Photocatalytic Performance

Nanomaterials ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1476 ◽  
Author(s):  
Petronela Pascariu ◽  
Mihaela Homocianu ◽  
Niculae Olaru ◽  
Anton Airinei ◽  
Octavian Ionescu
Keyword(s):  
Photocatalytic Performance ◽  
Molybdenum Trioxide ◽  
Blue Shift ◽  
Band Gap Energy ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
Electron Microscopies ◽  
Reaction Rate Constants ◽  
Transmission Electron ◽  
Electrospinning Method

New molybdenum trioxide-incorporated ZnO materials were prepared through the electrospinning method and then calcination at 500 °C, for 2 h. The obtained electrospun ZnO:MoO3 hybrid materials were characterized by X-ray diffraction, scanning and transmission electron microscopies, ultraviolet (UV)-diffuse reflectance, UV–visible (UV–vis) absorption, and photoluminescence techniques. It was observed that the presence of MoO3 as loading material in pure ZnO matrix induces a small blue shift in the absorption band maxima (from 382 to 371 nm) and the emission peaks are shifted to shorter wavelengths, as compared to pure ZnO. Also, a slight decrease in the optical band gap energy of ZnO:MoO3 was registered after MoO3 incorporation. The photocatalytic performance of pure ZnO and ZnO:MoO3 was assessed in the degradation of rhodamine B (RhB) dye with an initial concentration of 5 mg/L, under visible light irradiation. A doubling of the degradation efficiency of the ZnO:MoO3 sample (3.26% of the atomic molar ratio of Mo/Zn) as compared to pure ZnO was obtained. The values of the reaction rate constants were found to be 0.0480 h−1 for ZnO, and 0.1072 h−1 for ZnO:MoO3, respectively.

Synthesis of Zn Doped CdSe Quantum Dots via Inverse Micelle Technique

2014 ◽  
Vol 807 ◽  
pp. 115-121 ◽  
Author(s):  
Fatihah Aplop ◽  
Mohd Rafie bin Johan
Keyword(s):  
Quantum Dots ◽  
Quantum Confinement Effect ◽  
Blue Shift ◽  
X Ray Diffraction ◽  
Cdse Qds ◽  
Xrd Pattern ◽  
Transmission Electron ◽  
Inverse Micelle ◽  
Cadmium Selenide Quantum Dots ◽  
The Fourier Transform

Zinc doped Cadmium Selenide Quantum Dots (CdSe/Zn QDs) were synthesized via inverse micelle technique. The absorption spectra exhibit a strong blue-shift characteristic due to quantum confinement effect. The X-ray Diffraction (XRD) pattern showed the zinc-blende phase of Zn doped CdSe QDs. Transmission Electron Microscopy (TEM) images suggested that the sizes of QDs were falls in range between 2 – 8 nm, with narrow size distribution. The TEM images also revealed that the Zn doped CdSe QDs were spherical, having a compact and dense structure. The optical bandgap of Zn-doped CdSe QDs are smaller than the undoped CdSe QDs as shown in Tauc’s plot. The fourier transform infrared spectra proves the complexion of CdSe-Zn QDs.

TiO2 Nanoparticles Synthesized with Ti(SO4)2 as Precursor via the Hydrothermal Method and their Optical Absorption Properties

2017 ◽  
Vol 727 ◽  
pp. 280-283
Author(s):  
Xiao Ming Fu
Keyword(s):  
Hydrothermal Method ◽  
Ph Value ◽  
Blue Shift ◽  
Xrd Analysis ◽  
X Ray Diffraction ◽  
Absorption Properties ◽  
Tem Analysis ◽  
Visible Absorption ◽  
Transmission Electron ◽  
20 Nm

Anatase TiO2 particles of about 20 nm in the diameter were successfully synthesized with Ti (SO4)2 as titanium source and stronger ammonia water as precipitant at 240°C for 48 h with pH=5 using the hydrothermal method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and ultraviolet-visible absorption spectroscopy (UV-VIS). XRD analysis showed that the phase of the samples was anatase TiO2. TEM analysis confirmed that TiO2 particles of about 50 nm in the diameter were obtained when the pH value was 0.12. With the increasement of the pH value, the size of as-prepared TiO2 particles became remarkably fine. However, with the further increase of the pH value, the size of TiO2 particles was not obvious. TiO2 particles of about 20 nm in the diameter were obtained when the pH value was 5. And UV-VIS results showed that the size of anatase TiO2 nanoparticles, which became small, was propitious to the blue shift of their absorption peak.

Preparation and Wide Tunable Band-Gap Energies of PbTe Nanocrystals Using Glycerin as a Capping Ligand

2014 ◽  
Vol 904 ◽  
pp. 81-85
Author(s):  
Xing Li Ren ◽  
Xing Rong Jiang
Keyword(s):  
Band Gap ◽  
Blue Shift ◽  
Visible Range ◽  
X Ray Diffraction ◽  
Size Dependent ◽  
Near Ir ◽  
Transmission Electron ◽  
Novel Method ◽  
Uv Visible ◽  
Tunable Band Gap

PbTe nanocrystals (NCs) have been synthesized by a novel method at low temperature. Pb acetate being solved in glycerol and Te in TOP solution were used as the precursors for the preparation of PbTe nanocrystals. The as-prepared products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UVvis absorption, Fourier transform infrared spectroscopy (FTIR). These data, together with analysis of the absorption spectra, allowed us to observe the size dependence of the peaks in the absorption spectrum. The size-dependent optical spectra of the PbTe nanocrystals exhibits wide tunable band gap energies varying from UV visible range to near IR region, which corresponds to a huge blue shift of 3.0 eV in comparison to the bulk counterpart. Keywords: 1. PbTe nanocrystals, 2. optical properties, 3. wide tunable band gap, 4. microstructure

scholarly journals Optical Studies of Organically Functionalized Mn doped ZnS Quantum Dots

2021 ◽  
Vol 33 (12) ◽  
pp. 2972-2976
Author(s):  
Anju Bala ◽  
Rajeev Sehrawat ◽  
Renu Bala ◽  
Ashutosh Dixit
Keyword(s):  
Quantum Dots ◽  
Quantum Confinement Effect ◽  
Emission Spectra ◽  
Blue Shift ◽  
Capping Agent ◽  
X Ray Diffraction ◽  
Tem Analysis ◽  
Transmission Electron ◽  
Uv Visible ◽  
Mn Doped

Organically functionalized manganese doped zinc sulfide (ZnS/Mn) quantum dots were prepared by simple chemical method with polypyrrole (PPy) used as a capping agent. Prepared quantum dots were characterized with Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction microscope (XRD), UV-visible spectroscopy and photoluminescence spectroscopy. Crystalline size of PPy capped ZnS/Mn quantum dots for various concentrations of PPy were approximate 2 nm as analyzed by XRD and TEM analysis. The absorption spectra revealed the occurrence of a blue shift in the peak of absorption and an increase in the band gap value due to the quantum confinement effect. FTIR spectroscopy confirmed that shifting of broad peak at 2335.8 cm–1 was due to S-H stretching vibrations, which confirmed interaction of hydrogen and sulphur in ZnS/Mn/PPy nanocomposites. Uncapped ZnS/Mn and PPy capped ZnS/Mn quantum dots reveal the effective photoluminescence emission spectra in the range of 300-700 nm. With increase the value of capping agent in ZnS/Mn quantum dots, photoluminescence spectra going to red shifting. The photoluminescence properties of the organically functionalized ZnS nanoparticles are favourable for the application in optoelectronic devices.

Investigation of ZnFe2O4 Nanoparticles Prepared by High Energy Milling

2009 ◽  
Author(s):  
S. S. Srinivasan ◽  
N. Kislov ◽  
Yu. Emirov ◽  
D. Y. Goswami ◽  
E. K. Stefanakos
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Energy Gap ◽  
Blue Shift ◽  
High Energy ◽  
X Ray Diffraction ◽  
Force Microscopy ◽  
Atomic Force ◽  
Coefficient Estimation ◽  
Transmission Electron

Nanoparticles of Zinc Ferrite (ZnFe2O4) prepared by both wet- and dry- high-energy ball milling (HEBM), have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), surface area and pore size distribution (BET) and wavelength-dependent diffuse reflectance and scattering turned into absorption coefficient estimation using the Kubelka-Munk theory. It was found that after 72 hours of HEBM, the particle size was decreased from 220 nm for the initial material to 16.5 nm and 9.4 nm for the wet- and dry-milled samples, respectively. The optical absorption analysis revealed that the energy gap is increased (blue shift) by 0.45 eV for wet-milled and decreased (“anomalous” red shift) by 0.15 eV for dry-milled samples of ZnFe2O4 as the particle size decreased.

Electrical Conductivity of Quantum Size 2d Nanocomplex

2005 ◽  
Vol 23 ◽  
pp. 335-338 ◽  
Author(s):  
N. Gupta ◽  
H. Mallik ◽  
A. Sarkar
Keyword(s):  
Size Effect ◽  
Self Assembly ◽  
Energy Levels ◽  
Sol Gel ◽  
Quantum Size Effect ◽  
X Ray Diffraction ◽  
Distinctive Features ◽  
Quantum Size ◽  
Transmission Electron ◽  
Base Matrix

A nanocomplex of Chromium oxide nanoparticles with biopolymer matrix of gum Arabica is synthesized by natural self-assembly in chemical sol-gel route. Gum Arabica is chosen as base matrix due to its inherent biodegradable property. Experimental specimen of the said complex is prepared to satisfy near quantum size effect criterion. Due to near quantum size effect and spatial localization of nanoclusters, the developed specimen becomes an ideal 2D quantum well system. The longitudinal electrical conduction of the developed system is studied experimentally. Some of its structural aspects are also investigated to make the study conclusive. The dispersed cluster size is estimated by Transmission Electron Microscope (TEM) and X-ray diffraction (XRD). The results of I-V characteristics at temperatures 253 K show the distinctive features of localized energy levels. The spacing between energy levels near ground state to be comparable to the thermal energy at temperature 253 K for a cluster dimension below 10 nm. In this present study the developed specimens with the mentioned nanoclusters estimated from TEM and XRD as below 10 nm. The overall results are found to be encouraging.

SIZE-DEPENDENT PHOTOLUMINESCENCE AND ELECTROLUMINESCENCE OF COLLOIDAL CdSe QUANTUM DOTS

2013 ◽  
Vol 12 (02) ◽  
pp. 1350013 ◽  
Author(s):  
S. C. DEY ◽  
S. S. NATH
Keyword(s):  
Quantum Dots ◽  
Blue Shift ◽  
Diffraction Spectrum ◽  
Cdse Quantum Dots ◽  
X Ray Diffraction ◽  
Chemical Route ◽  
X Ray ◽  
Light Emitting Devices ◽  
Transmission Electron ◽  
Vis Spectroscopy

Here we adopt a convenient green chemical route for synthesis of CdSe quantum dots, their characterization by UV/Vis absorption spectroscopy, X-ray diffraction study and transmission electron microscopy. We carry out photoluminescence and electroluminescence spectroscopy to investigate the variation in electro-optical property with size. By UV/Vis spectroscopy, blue shift is revealed and bandgap is also calculated. X-ray diffraction spectrum reveals cubic structure and transmission electron micrographs show quantum dots of different size distributions (in the range 2–8 nm). Both the luminescence spectroscopies reveal green-orange luminescence depending upon the size distribution and indicate the possibility of using CdSe quantum dots as light emitting devices with better compatibility and faster response.

scholarly journals Quantum Confinement in GaP Nanoclusters

1994 ◽  
Vol 351 ◽  
Author(s):  
Bernhard K. Laurich ◽  
David C. Smith ◽  
Matthew D. Healy
Keyword(s):  
Quantum Confinement ◽  
Cluster Size ◽  
Blue Shift ◽  
X Ray Diffraction ◽  
High Crystalline Quality ◽  
Lattice Contraction ◽  
X Ray ◽  
Transmission Electron ◽  
Bulk Absorption ◽  
Distinct Line

ABSTRACTWe have prepared GaP and GaAs nanoclusters from organometallic condensation reactions of E[Si(CH3)3]3 (E = P, As) and GaCl3. The size of the as synthesized clusters is 10 Å to 15 Å. Larger clusters of 20 Å to 30 Å size were obtained by thermal annealing of the as grown material. X-ray diffraction and transmission electron microscopy confirm the high crystalline quality. A lattice contraction of 6.7% could be seen for 10 Å sized GaAs clusters. The clusters are nearly spherical in shape. Optical absorption spectra show a distinct line which can be assigned to the fundamental transition of the quantum confined electronic state. The measured blue shift, with respect to the GaP bulk absorption edge is 0.53 eV. As the cluster is smaller than the exciton radius, we can calculate the cluster size from this blue shift and obtain 20.2 Å, consistent with the results from X-ray diffraction of 19.5 Å for the same sample.

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