Structural and optical response of 2‐Mercaptoethonal capped CdS nanocrystals to Fe3+ ions

Cadmium sulfide (CdS) semiconductor nanocrystals (NCs) doped with Fe³⁺ have been synthesized via a solution‐based method utilizing dopant concentrations of (0–5%) and employing 2‐mercaptoehonal as a capping agent. X‐ray diffraction (XRD) results showed that the undoped CdS NCs are in mixed phase of cubic and hexagonal, where as the doped CdS NCs are in hexagonal phase. The crystallite size was increased from ∼1.2 nm to ∼2 nm. Diffuse reflectance spectroscopy studies (DRS) reveals that the band gap energy was decreased with Fe doping and it lies in the range of 2.58 ‐ 2.88 eV. Photoluminescence (PL) spectra of undoped CdS NCs show a strong green emission peak centered at 530 nm and a weak red emission shoulder positioned at 580 nm. After doping all the luminescence intensity was highly quenched and the green emission peak was shifted to orange region (580 nm), but the position of weak red emission shoulder was unaltered with doping. FTIR studies revealed that the NCs were sterically stabilized by 2‐mercaptoethanol. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology and photoluminescence properties of ZnO nanostructures fabricated with different given time of Ar

ZnO nanostructures were grown on Au‐coated Si (100) substrates by carbonthermal reduction method with the help of Ar at the beginning of growth. The structural and optical properties of ZnO nanostructures strongly depended on the supply time of Ar. When the given time of Ar gas current was 90s, sample was ZnO nanowires with hexagonal morphology. The Raman spectroscopy revealed the low level of oxygen vacancies and Zn interstitials in samples. Room temperature photoluminescence (PL) spectra exhibited the intensity of green emission increased on the condition of rich oxygen (decrease given time of Ar) and the nanowire had strongest intensity of UV emission compared with other nanostructures. Green emission is ascribed to the electron transition from the bottom of the conduction band to the antisite defect O_Zn level. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared photoluminescence from TlGaS2 layered single crystals

Photolimuniscence (PL) spectra of TlGaS₂ layered crystals were studied in the wavelength region 500‐1400 nm and in the temperature range 15‐115 K. We observed three broad bands centered at 568 nm (A‐band), 718 nm (B‐band) and 1102 nm (C‐band) in the PL spectrum. The observed bands have half‐widths of 0.221, 0.258 and 0.067 eV for A‐, B‐, and C‐bands, respectively. The increase of the emission band half‐width, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature are explained using the configuration coordinate model. We have also studied the variations of emission band intensity versus excitation laser intensity in the range from 0.4 to 19.5 W cm^‐2. The proposed energy‐level diagram allows us to interpret the recombination processes in TlGaS₂ crystals. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and photoluminescence properties of bundle‐like CdS nanostructures assembled by high‐quality nanorods

Bundle‐like cadmium sulfide (CdS) nanostructures assembled by high‐quality nanorods have been successfully synthesized on a large scale via a facile solvothermal route in a mixed solvent of ethylenediamine and dodecanethiol. The typical lengths of bundle‐like CdS nanostructures are several tens of micrometers, and the diameters and lengths of CdS nanorods are about 50–70 nm and several micrometers, respectively. The influence of the concentration of dodecanethiol on the morphologies of CdS nanostructures has been investigated carefully. Photoluminescence spectra (PL) of CdS nanostructures reveal that the bundle‐like CdS nanostructures exhibited two fluorescence emission peaks centered at 495nm (2.51 eV) and 522 nm (2.38 eV) as the excitation wavelength is 405 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of ZnO nanotubes

Tubular ZnO nanostructures have been obtained via a hydrothermal method at low temperature (90 °C) without any catalysts or templates. The XRD measurement reveals that the tubes are single crystals with hexagonal wurtzite structure. SEM shows that the diameters of ZnO nanotubes ranged from 400 to 550 nm. The Raman and PL spectra indicate that oxygen vacancies or Zn interstitials are responsible for the green emission in the ZnO nanotubes. A possible growth mechanism on the formation of crystalline ZnO nanotubes has been presented. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,structure and optical properties of zinc oxide hexagonal microprisms

Zinc oxide (ZnO) pencil‐head‐like (PHL) microprisms were synthesized by a hydrothermal route using a zinc (Zn) plate as a source and substrate. The structural analysis confirmed the formation of ZnO with hexagonal wurtzite phase on the hexagonal Zn substrate and the growth of the ZnO microparticles along the [101] direction. The room temperature photoluminescence (PL) of the ZnO microprisms showed a sharp UV emission band located at around 380 nm, which is expected to originate from the radiative recombination of free excitons. The sharp UV emission band, with a full width at half‐maximum of about 15 nm and an extremely weak visible emission, confirms the high crystal quality of the synthesized ZnO microprisms. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization and optical properties of ZnS nanorods branched out from ZnS film on Zn foil

Complex nanomaterial‐film‐metal substrate architectures, which are composed of ZnS nanorods, island‐like ZnS film and Zn foil, have been formed via a simple vapor deposition route. The growth of the complex nanostructures is initiated by the preferred formation of ZnS film, and ZnS nanorods branches out from ZnS film flows a liquid‐phase epitaxial growth mode. The ZnS nanorod is switched to an angle, which may be attributed to the sudden change of vapor pressure and temperature reduction by the end of vapor deposition process. The room‐temperature photoluminescence spectrum shows that complex ZnS nanostructures have a strong blue emission band centered at about 423 nm and a weak broad green emission band centered at about 515 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Excitation intensity and temperature‐dependent photoluminescence and optical absorption in Tl4Ga3InSe8 layered crystals

Photoluminescence (PL) spectra of Tl₄Ga₃InSe₈ layered crystals grown by Bridgman method have been studied in the wavelength region of 600‐750 nm and in the temperature range of 17‐68 K. A broad PL band centered at 652 nm (1.90 eV) was observed at T = 17 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.13 to 55.73 mW cm^‐2 range. Radiative transitions from donor level located at 0.19 eV below the bottom of conduction band to shallow acceptor level located at 0.03 eV above the top of the valence band were suggested to be responsible for the observed PL band. From X‐ray powder diffraction and optical absorption study, the parameters of monoclinic unit cell and the energy of indirect band gap were determined, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of radial‐like ZnO structure by hydrothermal method with ZnSO4·7H2O and Zn(CH3COO)2·2H2O as zinc sources

Radial‐like ZnO structures were prepared using zinc sulfate (ZnSO₄·7H₂O) and zinc acetate [Zn(CH₃COO)₂·2H₂O] as zinc sources by a facile template‐free hydrothermal method in this paper. Structural and optical properties of radial‐like ZnO structures are characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV‐vis spectrophotometer and photoluminescence measurement (PL). It has been found that the distinct surface morphologies of radial‐like ZnO structures grown by different zinc sources. Slim radial‐like ZnO with a hexagonal wurtzite structure is grown by using ZnSO₄·7H₂O as zinc sources, whereas coarse radial‐like ZnO with zincite structure is achieved by zinc acetate. The UV‐vis absorption spectra of them both display an obvious and significant absorption in the ultraviolet region. The room temperature PL spectra of ZnO structures grown by two different zinc sources possess a common feature that consists of a strong ultraviolet (UV) peak and visible emission band.     

Structural and magnetic studies of Mn‐doped ZnO

The bulk samples of Mn‐doped ZnO were synthesized with the nominal compositions Zn_1‐xMn_xO (x = 0.02, 0.05, 0.10, 0.15) by the solid‐state reaction and sol‐gel methods. In both the methods the samples were finally sintered at ∼700 °C in air. The X‐ray diffraction (XRD) studies of the samples synthesized by the solid‐state reaction method exhibit the presence of wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples, suggesting that doped Mn ions sit at the regular Zn sites. However, same studies spread over the samples with Mn content ≥5% and synthesized by the sol‐gel method reveal the occurrence of some secondary phase in addition to the majority wurtzite phase. The magnetic measurements by vibrating sample magnetometer (VSM) clearly indicate ferromagnetic interaction at room temperature in all the samples. The Curie temperatures (T_c) and magnetization vary with concentration of Mn ions in the samples. However, the samples synthesized by sol‐gel method were found to have lower Tc values and also lower magnetization as compared to the corresponding samples synthesized by solid‐state reaction method. It could possibly be due to the presence of antiferromagnetic islands and smaller crystallite sizes in the samples prepared by sol‐gel method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation,structure and photoluminescence properties of SiO2–coated ZnS nanowires

It is essential to passivate one‐dimensional (1D) nanostructures with insulating materials to avoid crosstalking as well as to protect them from contamination and oxidation. The structure and influence of thermal annealing on the photoluminescence properties of ZnS‐core/SiO₂‐shell nanowires synthesized by the thermal evaporation of ZnS powders followed by the sputter deposition of SiO₂ were investigated. Transmission electron microscopy and X‐ray diffraction analyses revealed that the cores and shells of the core‐shell nanowires were single crystal zinc blende‐type ZnO and amorphous SiO₂, respectively. Photoluminescence (PL) measurement showed that the core‐shell nanowires had a green emission band centered at around 525 nm with a shoulder at around 385 nm. The PL emission of the core‐shell nanowires was enhanced in intensity by annealing in an oxidative atmosphere and further enhanced by subsequently annealing in a reducing atmosphere. Also the origin of the enhancement of the green emission by annealing is discussed based on the energy‐dispersive X‐ray spectroscopy analysis results. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Homoepitaxial growth and photoluminescence of self‐assembled In‐doped ZnS nanowire bundles

Self‐assembled In (Indium)‐doped ZnS nanowire bundles were synthesized via a thermal evaporation method without using any template. Vapor ‐ solid homoepitaxial growth was found to be the key reason for the formation of close‐packed nanowire bundles grown on the surface of microscale sphere‐shaped ZnS crystal. X‐ray diffraction (XRD), selected area electron diffraction (SAED), and transmission electron microscopy (TEM) analysis demonstrate that the In‐doped ZnS nanowires have the cubic structure, and there are numerous stacking faults along the <111> direction. Photoluminescence (PL) spectrum shows that the spectrum mainly includes two parts: a weak violet emission band centering at about 380 nm and a strong green emission band centering at about 510 nm. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controllable synthesis of novel In2O3 nanostructures and their field emission properties

Three kinds of novel indium oxide (In₂O₃) nanostructures, namely, nanorods, nanoflowers and nanowhiskers were synthesized on silicon substrate via a simple vapor‐phase transport method under atmospheric pressure. The In₂O₃nanostructures were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy‐dispersive X‐ray spectrometer (EDS) spectrum. The Raman spectra of these nanostructures showed four sharp scattering peaks centered at 308, 365, 522, and 628 cm^‐1, whose position and intensity were characteristic of standard Raman spectra for In₂O₃. The Room‐temperature photoluminescence (PL) spectra showed visible emissions centered around 576, 592, and 624 nm. Field emission measurements demonstrated that the nanoflowers possessed the best performance with a turn‐on field of 3.54 V/µm and a threshold field of 9.83 V/µm. And the field enhancement factors of these nanostructures are high enough for the application of field emission display devices. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and field emission properties of SnO2 nanowalls

SnO₂ nanowalls were synthesized on silicon substrate by the thermal chemical vapor transport method at a low temperature of around 650 °C under atmospheric pressure. The microstructure and morphology of the SnO₂ nanowalls were evaluated by using scanning electron microscopies and X‐ray diffraction. Room temperature photoluminescence spectra of the nanowalls showed a broad emission band centering at about 530 nm. Field emission measurements demonstrated that the nanowalls possessed good performance with a turn‐on field of ∼3.5 V/μm and a threshold field of ∼6.1 V/μm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flux Bridgman growth and the influence of annealing temperatures on PL properties of ZnO single crystals

Transparent ZnO crystals were obtained by the flux Bridgman method from high temperature solution of 22 mol% ZnO‐78 mol% PbF₂ system. The influence of annealing temperatures on the photoluminescence (PL) of ZnO crystal was investigated. An ultraviolet emission peak at about 379 nm was observed in PL spectra and the peak position has a weak blueshift for annealed samples. A green band centered at 523 nm appeared in the annealed samples and its intensity enhanced with the increase of annealing temperatures, while the intensity of the ultraviolet peak decreased considerably. However, the ultraviolet emission peak became the strongest after annealing at 1000 °C. This phenomenon was considered to be associated with oxygen vacancy and F^‐ impurities induced by the PbF₂ flux. The results show that high temperature annealing in air seems helpful for improving the PL properties of ZnO crystal. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and luminescence properties of large‐scale zinc oxide nanotetrapods

Large‐scale zinc oxide (ZnO) nanotetrapods have been grown on p‐type Si (111) substrate by oxidizing zinc pieces in air by thermal evaporation technique without the presence of any catalyst. The size and morphology of the nanostructures was found to depend on experimental parameters. The grown nanostructures were characterized by X‐ray Diffraction (XRD), Photoluminescence (PL), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and analysis of elemental composition was done by Energy Dispersive X‐ray analysis (EDX). The EDX spectrum shows that the grown product contains Zn and O only. The X‐ray diffraction pattern indicates that the microstructure of the obtained products is typical hexagonal wurtzite ZnO. The optical properties were studied using room temperature PL spectroscopy which indicates that the products are of high optical quality and the near band edge UV transition peak intensity increases with decrease in tetrapod size. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis via an organic molten salt solvent route and characterization of PbS nanocrystals

In this paper, four petals flowers‐like and quasi sphere‐like PbS nanostructures were successfully synthesized by an environment friendly organic molten salt solvent (OMSS) route at 200 °C, with different sulfur sources, e.g. thiourea and sodium thiosulfate, respectively. The as‐synthesized products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), UV–vis absorption spectrum and photoluminescence (PL) spectrum, respectively. It was shown that four petals flowers‐like and quasi sphere‐like PbS nanocrystals were formed. It was also demonstrated that the morphologies of PbS nanocrystals were significantly influenced by different sulfur sources. The ultraviolet‐visible absorption peaks of PbS nanocrystals exhibited a large blue‐shift and the luminescence spectra had strong and broad emission bands centered at 488 nm and 492 nm. The possible formation mechanisms of the PbS nanostructures were discussed. The organic molten salt solvent (OMSS) method is preferable for synthesizing high‐quality PbS nanocrystals. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

表面活性剂对水热法合成ZnS:Cu,Al纳米晶光致发光特性的影响

采用水热法直接合成了ZnS∶Cu,Al纳米荧光粉,并且系统研究了加入表面活性剂在不同S/Zn下,清洗样品和不清洗样品的结晶性、傅立叶红外光谱(FT-IR)及光致发光(PL)光谱.XRD和TEM测试结果表明:合成纳米晶为纯立方相结构,球形纳米晶尺寸约15 nm, 尺寸分布窄,分散性好.未清洗样品的结晶性比清洗样品的好,且加入表面活性剂和未清洗都导致粒径增大,影响纳米材料的表面态.改变[S~(2-)]/[Zn~(2+)]物质的量比、清洗和加入表面活性剂都会影响材料的PL强度.这说明其发光机理为紫外光激发材料表面的发光中心,即PL强度决定于纳米材料的表面态.     

Photoluminescence Spectra of GaS0.75Se0.25 Layered Single Crystals

Photoluminescence (PL) spectra of GaS_0.75Se_0.25 layered single crystals have been studied in the wavelength region of 500‐850 nm and in the temperature range of 10‐200 K. Two PL bands centered at 527 ( 2.353 eV, A‐band) and 658 nm (1.884 eV, B‐band) were observed at T = 10 K. Variations of both bands have been studied as a function of excitation laser intensity in the range from 8 × 10^‐3 to 10.7 W cm^‐2. These bands are attributed to recombination of charge carriers through donor‐acceptor pairs located in the band gap. Radiative transitions from shallow donor levels located 0.043 and 0.064 eV below the bottom of conduction band to acceptor levels located 0.088 and 0.536 eV above the top of the valence band are suggested to be responsible for the observed A‐ and B‐bands in the PL spectra, respectively.     

Low temperature synthesis of spindle‐like ZnO nanostructures under microwave irradiation

A simple and general microwave route is developed to synthesize nanostructured ZnO using Zn(acac)₂·H₂O (acac = acetylacetonate) as a single source precursor. The reaction time has a great influence on the morphology of the ZnO nanostructures and an interesting spindle‐like nanostructure is obtained. The microstructure and morphology of the synthesized materials are investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), field‐emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). It is found that all of them with hexagonal wurtzite phase are of single crystalline structure in nature. Ultraviolet–visible (UV‐vis) absorption spectra of these ZnO nanostructures are investigated and a possible formation mechanism for the spindle‐like ZnO nanostructures is also proposed.