Optical properties of water-soluble Co:ZnS semiconductor nanocrystals synthesized by a hydrothermal process

Water-soluble ZnS:Co²⁺ nanocrystals (NCs) were synthesized by a low temperature hydrothermal process using 3-mercaptopropionic acid (MPA) as capping agent and the influence of doping on the optical properties of ZnS:Co²⁺ NCs was investigated. It was found that the ZnS:Co²⁺ NCs are highly crystalline and show zinc blende structure with an average particle size of about 7 nm. The lattice constant of the ZnS:Co²⁺ NCs decreases slightly by the introduction of Co²⁺. The Co dopants were well doped into the ZnS:Co²⁺ NCs, as confirmed by X-ray photoelectron spectroscopy(XPS) and the ⁴A₂(F) → ⁴T₁(P) transition of Co²⁺ was detected from the UV-vis absorption spectra. The absorption edge of the ZnS:Co²⁺ NCs is blue-shifted as compared with that of bulk ZnS, indicating the quantum confinement effect. The PL intensity of the NCs shows the maximum value when the Fe-doping concentration is 0.5 at.%.     

Effects of Ni2+ concentration and vacuum annealing on structure,morphology and optical properties of Ni doped ZnS nanopowders synthesized by hydrothermal method

Ni doped ZnS nanopowders were synthesized by hydrothermal method. The as-synthesized ZnS nanopowders possessed zinc blende structure with the particle sizes of ～20?nm, and they display a broad emission band from 400?nm to 700?nm centered at ～540?nm. The influence of Ni²⁺ doping and vacuum annealing on the structure, morphology and optical properties was investigated systematically. The results revealed that the emission peaks are blue shifted with Ni²⁺ doping, and the emission peaks of 0.2, 0.4, 0.6, 0.8 and 1.0?mol% Ni²⁺ doped ZnS nanopowders are centered at ～520, ～ 510, 500, 490 and 470?nm, respectively. While, the zinc blende phase transformed to wurtzite phase when annealing at 600?°C or higher, and the annealed samples exhibited three emission peaks positioned at ～490, ～547 and ～580?nm. The results indicated that the as prepared Ni²⁺-doped ZnS nanopowders have a potential application in LED as light conversion layer.     

The evolution of optical properties during hydrothermal coarsening of ZnS nanoparticles

Nearly monodisperse 3-nm ZnS nanoparticles capped with the mercaptoethanol were prepared in aqueous solution. During hydrothermal coarsening of ZnS nanoparticles, the evolution of optical properties and growth kinetics were investigated. As the particle size increased, the absorbance spectrum continued a size-dependent shift to long wavelength. A significant enhancement in photoluminescence was obtained during the growth, indicating the decrease of defects and the increase of ZnS crystallinity. The average particle size and size distribution were calculated from the absorption spectra, which revealed two-stage growth kinetics of ZnS nanoparticles.     

ZnS:Mn荧光粉的溶剂热法制备及其发光性能

采用溶剂热法合成了ZnS∶Mn荧光粉,讨论了锰掺杂量对硫化锌发光性能的影响。通过扫描电镜(SEM)、X射线粉末衍射仪(XRD)、紫外可见分光光度计(UV-Vis)和荧光分光光度计(PL)对合成的ZnS∶Mn荧光粉的结构和光学性能进行了表征。结果表明:ZnS∶Mn荧光粉的平均粒径为13.5nm,在波长340nm~200nm处有强吸收,Mn离子浓度在所研究范围内,锰掺杂量对硫化锌的晶型、结晶度、粒径无影响,但对其能级结构影响显著,且随着Mn离子掺杂量的增加,发光强度先增加后减小,掺杂量为5%时达到最大值。     

Fabrication and optical properties of needle-like ZnO array by a simple hydrothermal process

A simple low temperature hydrothermal process was employed to fabricate the needle-like ZnO array in the diluted butyl amine. The microstructure, morphology and the photoluminescence property of the as-prepared products were characterized by x-ray diffraction (XRD), transmission electron microscope (TEM), field emission environment scanning electron microscope (SEM) and photoluminescence spectrum (PL). The results show that the needle-like ZnO crystals are hexagonal wurtzite monocrystal with slender figure and smooth surface. A possible growth mechanism of the needle-like ZnO array related to the diluted butyl amine is proposed. The PL spectrum of the needle-like ZnO array shows a strong blue light emission at 437 nm and a relatively low ultraviolet emission at 377 nm.     

The light emission properties of ZnS:Mn nanoparticles

ZnS and Mn-doped ZnS nanoparticles were synthesized via a simple hydrothermal synthesis method. The former emits super bright blue fluorescence light while the latter exhibits super-bright yellow light under a fluorescence microscope. Accordingly, their photoluminescence peaks are located at 420 nm and 580 nm in the spectra excited with 281 nm and 335 nm wavelengths, respectively. The super-bright ZnS:Mn nanoparticles can be used as a yellow fluorescence powder in making LED and plat display, and can be used as biological fluorescence probe to replace CdSe, CdS quantum dos without any damage to mankind and environment.     

Controllable synthesis and luminescence properties of TiO2:Eu3+ nanorods,nanoparticles and submicrospheres by hydrothermal method

Eu³⁺-doped TiO₂ nanocrystals with three kinds of morphologies (nanorods, nanoparticles, and submicrospheres) have been successfully fabricated in cetyltrimethylammonium bromide (CTAB)/water/cyclohexane/n-pentanol reverse micelle by hydrothermal method for the first time and their photoluminescence (PL) properties have also been studied. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), FT-IR, and PL spectra were used to characterize the samples. The acidic and alkaline conditions of the microemulsion play an important role in determining the geometric morphologies of the final products. TiO₂:Eu³⁺ with three different morphologies all exist only in anatase phase and show high luminescence intensity without further calcinations, which show its advantages of energy saving. The shape of emission spectra was independent of the morphologies of the products but the luminescence intensity of the TiO₂:Eu³⁺ materials is strongly dependent on their morphology. The results show that TiO₂:Eu³⁺ nanorods possess the strongest luminescence intensity among the three nanostructured samples.     

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.     

Thin films containing Mn-doped ZnS nanocrystals synthesised by chemical method and study of some of their optical properties

In this article, we present the optical properties of thin films containing Mn-doped ZnS nanocrystals synthesised by the chemical method. The ZnS nanoparticles within the polymer matrix (polyvinyl alcohol) were investigated by SEM and TEM images and analysed by X-ray diffraction. The effect of polymer concentration on the direct band gap of Mn-doped ZnS thin films was calculated from the data for absorption measurements. The values of the band gap are in the range of 3.73–3.90?eV. In addition, we discuss the photoluminescence of these films.     

水热法合成高发光强度ZnS:Cu,Al纳米荧光粉研究

采用水热法直接合成了高发光强度的ZnS:Cu,Al纳米荧光粉.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15nm,尺寸分布窄,分散性好.首次系统地研究了不同[S2-]/[Zn2+]和[Al3+]/[Cu2+]比值对清洗样品和不清洗样品的光致发光(PL)光谱的影响.实验结果表明,激活剂浓度不变而改变[S2-]/[Zn2+]摩尔比时,发光强度显著变化,同时未清洗样品的PL强度均比清洗样品的强,且未清洗样品强度增强的比值在低的[S2+]/[Zn2+]时更显著.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,此外掺杂的激活剂摩尔比同样对PL光谱有影响.在我们的实验中,用343nm紫外光激发时,n[S2-]:n[Zn2+]=3,n[Al3]:n[Cu2+]=2时未清洗样品的发光最强,此时于室内照明条件下可观察到明亮的绿光.     

Optical properties of nanocrystalline ZnS films prepared by high pressure magnetron sputtering

Nanocrystalline ZnS films with different thickness (10–40 nm) were deposited onto quartz and NaCl substrates by magnetron sputtering of a ZnS target in argon plasma. All the films showed a zinc blende structure and the photoluminescence peak positions depended on the surface to volume ratio of the films. The optical absorption in these films could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites.     

Optical and photocatalytic properties of sulfide semiconductor quantum dots (QDs) synthesized by silk fibroin template

Bio-template method is a simple, controllable and environmental friendly strategy to synthesize nanomaterials. It also avails the formation of bioactive and biocompatible nanoparticle–biomolecule hybrid for biotechnical applications. In this paper, silk fibroin was first successfully used as biomolecule template for the biomimic synthesis of CdS and ZnS quantum dots (QDs). The QDs showed promising applications as fluorescence probes and nanocatalysts. The effect of preparation situation to their optical and photocatalytic properties was well researched and CdS QDs with satisfying catalytic activities could be achieved by adjusting the protein matrix. It offers us a low-cost and effective way to synthesize series of sulfide semiconductor nanomaterials using silk fibroin.     

Structural and photoluminescence properties of aligned Sb-doped ZnO nanocolumns synthesized by the hydrothermal method

Aligned Sb-doped ZnO nanocolumns were synthesized by a simple hydrothermal method. Based on the analyses of the X-ray diffraction and photoluminescence result, it could be confirmed that the Sb has successfully doped in the ZnO crystal lattices to form an accepter energy level. At 85 K, the recombination of the acceptor-bound exciton was predominant in PL spectrum, which was attributed to the transition of the (Sb_Zn-2V_Zn) complex bound exciton. The acceptor binding energy had been calculated to be 123 meV.     

水溶性ZnS量子点的共沉淀法制备、 表征及其光学性能

以硫化钠和乙酸锌为反应物,3-巯基丙酸为表面包覆剂,利用共沉淀法制备了水溶性ZnS量子点。并采用X射线衍射仪、透射电子显微镜和荧光分光光度计等对样品的结构、形貌、粒径和光学性能进行了表征。结果表明:所得样品为ZnS立方型闪锌矿结构,量子点的形状呈不规则球形,粒径主要集中在4.8nm左右;样品在585～590nm之间出现了黄色荧光发射波峰。同时,利用红外光谱对ZnS量子点的合成机理进行了初步分析。     

Magnetic chains of Co spheres synthesized by hydrothermal process under magnetic field

Hydrothermal process under magnetic fields is successfully used to synthesize Co chains using reduction approach by carefully controlling the reaction conditions. The formation of the chain structure might be that magnetic fields drive the nanoscale crystals of Co to form chains. The Co sphere size and chain length are analyzed by X-ray diffraction (XRD) and scan electron microscopy (SEM). The result of the vibrating sample magnetometer (VSM) shows that the magnetic chains possess the saturation magnetization of 102 emu/g. The factors on the magnetic properties of the magnetic nanochains are discussed.     

The effect of annealing on structural, electrical and optical properties of nanostructured ZnS/Ag/ZnS films

In this paper a ZnS/Ag/ZnS (ZAZ) nano-multilayer structure is designed theoretically and optimum thicknesses of ZnS and Ag layers are calculated at 35 and 17 nm, respectively. Several conductive transparent ZAZ nano-multilayer films are deposited on a glass substrate at room temperature by thermal evaporation method. Changes in the electrical, structural, and optical properties of samples are investigated with respect to annealing in air at different temperatures. High-quality nano-multilayer films with the sheet resistance of 8 Ω/sq and the optical transmittance of 83% at 200 °C annealing temperature are obtained. The figure of merit is applied on the ZAZ films and their performance as transparent conductive electrodes are determined.     

化学水浴法制备ZnS薄膜光学性能

利用薄膜分析系统测量不同沉积时间制备的ZnS薄膜透射谱,通过分析薄膜透射谱,来确定ZnS薄膜光学常数和禁带宽度.实验结果表明,在线性生长阶段,薄膜的沉积速率大约为1 nm/min,具有很好的线性关系,沉积0.5 h的ZnS薄膜在可见光范围内光透过率为82%左右.     

Superhydrophobic Behavior and Optical Properties of ZnO Film Fabricated by Hydrothermal Method

ZnO film with claviform structure was synthesized on quartz substrates through a hydrothermal method at 90℃.The microstructure of the film is composed of clusters of submicrometer rods,which therefore endues the film with good superhydrophobicity.Meanwhile,the film with such tanglesome structure also shows highly crystalline quality testified by a strong ultra-violet (UV) emission and very low deep-level emission observed on the photoluminescence (PL) spectrum as well as high transparence of about 89% transmittance in visible light range.     

Photoluminescence and field emission properties of ZnS:Mn nanoparticles synthesized by rf-magnetron sputtering technique

Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size 6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm.     

Investigation on one-pot hydrothermal synthesis,structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 °C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450–500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products.