共查询到20条相似文献,搜索用时 31 毫秒
1.
Ana Stanković Zoran Stojanović Ljiljana Veselinović Srečo Davor Škapin Ines Bračko Smilja Marković Dragan Uskoković 《Materials Science and Engineering: B》2012,177(13):1038-1045
In this paper, we investigate the effect of the particle size and morphology on the optical properties of ZnO. A series of ZnO micro and nanocrystals were synthesized by the hydrothermal processing of zinc acetate dihydrate and sodium hydroxide as the starting materials, and polyvinylpyrrolidone (PVP) as the polymer surfactant. The particle size and morphology were tailored by adjusting the reactant molar ratios [Zn2+]/[OH−], while the reaction temperature and the time remained unchanged. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM) have shown that the micro and nanocrystals have a high crystalline pure wurtzite-type hexagonal structure with nanosized crystallites. The size and morphology of the ZnO micro and nanocrystals were investigated by field emission scanning electron microscopy (FE-SEM), which showed a modification from micro-rods via hexagonal-faceted prismatic morphology to nanospheres, caused by simple adjustment of the reactant molar ratio [Zn2+]/[OH−] from 1:1 to 1:5. The optical properties of the ZnO micro and nanocrystals, as well as their dependence on the particle size and morphology were investigated by Raman and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS). The UV–vis spectra showed that the modification of the particle size and morphology from nanospheres to micro-rods resulted in increased absorption, and a slight red-shift of the absorption edge (0.06 eV). Besides, the band gap energy of the synthesized ZnO micro and nanocrystals showed the red shift (∼0.20 eV) compared to bulk ZnO. According to the results of a Raman spectroscopy, the enhanced visible light absorption of the ZnO micro and nanocrystals is related to two phenomena: (1) the existence of lattice defects (oxygen vacancies and zinc interstitials), and (2) the particle surface sensitization by PVP. 相似文献
2.
In this paper, we report on the synthesis of size-dependent blue luminescent CdS nanocrystals by using a new nonhydrolytic single-source molecular method. The size of the synthesized CdS nanocrystals could be easily controlled by adjusting the ratio of reaction sources under inert atmosphere. The studies on the optical properties reveal an obvious size-dependent photoluminescence characteristic of the synthesized nanocrystals. 相似文献
3.
《Materials Research Bulletin》2013,48(11):4521-4525
Metal oxide nanoparticles have potential use in energy storage, electrode materials, as catalysts and in the emerging field of nanomedicine. Being able to accurately tailor the desirable properties of these nanoceramic materials, such as particle size, morphology and optical bandgap (Eg) is integral in the feasibility of their use. In this study we investigate the altering of both the structure and physical properties through the doping of hematite (α-Fe2O3) nanocrystals with cerium at a range of concentrations, synthesised using a one-pot co-precipitation method. This extremely simple synthesis followed by thermal treatment results in stable Fe2−xCexOy nanoceramics resulting from the burning of any unreacted precursors and transformation of goethite-cerium doped nanoparticle intermediate. The inclusion of Ce into the crystal lattice of these α-Fe2O3 nanoparticles causes a significantly large reduction in mean crystalline size and alteration in particle morphology with increasing cerium content. Finally we report an increase optical semiconductor bandgap, along with a substantial increase in the ultraviolet attenuation found for a 10% Ce-doping concentration which shows the potential application of cerium-doped hematite nanocrystals to be used as a pigmented ultraviolet filter for cosmetic products. 相似文献
4.
Biljana Pejova 《Materials Research Bulletin》2008,43(11):2887-2903
Some aspects regarding the optical and photoelectrical properties of bismuth(III) sulfide nanocrystals deposited in thin film form were studied. The influence of electrostatic interaction between photogenerated charge carriers on the shape of the spectral dependence of absorption coefficient for as-deposited and thermally treated nanocrystalline Bi2S3 thin films was investigated. The experimentally obtained spectral dependencies of the optical absorption coefficient were analyzed using the models of Elliott and Toyozawa. It was shown that the sub-band gap optical absorption of the studied films is of exponential type. A modified Urbach rule function was employed to calculate the relevant parameters which determine the value of critical energy at which a transition between the two main absorption regimes occurs in studied semiconductor. Experimentally obtained changes of Urbach energies (i.e. tailing parameters) upon thermal treatment of the films were explained in terms of the differences in the degree of structural disorder of the as-deposited and annealed films according to the model of Cody. The experimental optical absorption data were also used to model the photoconductivity spectral response of thermally annealed films using various approaches. 相似文献
5.
Silica based sol-gel coatings doped with different silver amounts have been prepared. Apart from silver concentration, other experimental parameters such as thermal densification conditions, presence of other co-dopants and the nature of the substrate have been varied in order to determine their influence on the final microstructure and properties. Characterisation of the materials prepared was carried out by optical spectroscopy (photoluminescence and absorption), secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). The study was oriented to determine the parameters governing the nucleation and growth of silver nanoparticles. The results showed that formation of silver nanoparticles was promoted when one or more of the following conditions were achieved: silver concentration in the initial sol over 5%, thermal densification under reducing atmosphere and use of pure silica substrate (in general, glass substrates without modifier ions and, therefore, with few non-bridging oxygen positions). 相似文献
6.
R.S. Sonawane 《Materials Research Bulletin》2008,43(3):618-624
A new phosphate glass system with CdS nanocrystals dispersed in glass matrix was investigated. The phosphate glass composition with good stability has been used for preparation of CdS doped glasses. The CdS in the range of 0.5-7.0% has been doped into this glass composition. Effect of CdS content on the optical and other properties has been investigated. The optical characterization of the glass samples showed that with increasing concentration of CdS, there was a red shift in transmission cut-off of the glasses. From the transmission cut-off of each glass sample, the band gap of the CdS nanocrystals embedded glass was calculated. The band gap of CdS particles embedded glass was observed in the range of 3.1-4.1 eV. The present system is compared with CdS nanocrystals doped in silica based glass system. In the phosphate glass system, the UV transmission cut-off's are not sharp and the optical transmittance decreases with increasing CdS content in contrast to silica glass system. The reason for such behavior has been discussed in the present investigation. TEM of the CdS doped phosphate glasses showed CdS particle size in the range of 5-7 nm for lower concentration of CdS and 10-100 nm for higher concentration of CdS. The nanocrystals are non-uniform in size but uniformly dispersed in glass matrix. 相似文献
7.
Trilochan Sahoo Jong Hyeob Baek Jin Soo Kim Cheul-Ro Lee 《Materials Research Bulletin》2011,46(4):525-530
The presence of the complexing agents in the growth solution poses risk of the unintentional doping in the synthesized product and hence is likely to adversely affect the intrinsic properties. Herein we report the synthesis of ZnO nanoparticles with porous microstructure using pure aqueous precursor. Crystalline ZnO nanoparticles were synthesized by thermal treatment of aqueous solution of zinc acetate in an open bath. The size of the nanocrystals was controlled by changing the initial precursor concentration. The structural and optical properties of the synthesized nanocrystals were analyzed by X-ray diffraction, high resolution transmission electron microscopy, UV-vis absorption and room temperature photoluminescence measurement techniques. The TEM and UV-vis spectral signature analyses confirmed the formation of dispersed single crystalline ZnO nanoparticles. The nanopowders were found to have disordered mesoporous structure. The synthesized nanocrystals exhibited characteristic band edge emission as well as to surface defect related deep level visible luminescence. 相似文献
8.
Dye Coumarin 151 was postgrafted into the rodlike SBA-15 mesoporous materials, which were synthesized by a direct hydrothermal synthesis method and further modified by an organic silane with a terminal amino group. Characterization by powder X-ray diffraction, N2 adsorption-desorption, transmission electron microscopy, photoluminescence and scanning electron microscopy were carried out. Small-angle X-ray diffraction and N2 adsorption-desorption characterizations showed that these dye containing materials remained as ordered mesostructures and the pore size was from 6 nm for blank sample to 3.6 nm for postgrafting sample. PL characterization of composite samples exhibited optical properties with different dye concentrations. The characterization showed the existence of Coumarin 151 in the channels of SBA-15 and the composite materials with novel optical properties enabled possible applications in optical sensing and electron acceptors. 相似文献
9.
Synthesis and characterization of CuInS2 powder sample prepared by a simple and convenient solvothermal method is reported. The influence of the variation of Cu/In molar ratio from 0.69 to 1.25 on the particle morphology, crystal structure and optical properties of CuInS2 samples was studied. The X-ray diffraction studies indicated that the samples were polycrystalline in nature. SEM images of the samples revealed that the copper-rich products were uniform microspheres with smooth surfaces, whereas microspheres formed by network of interconnected flakes were obtained for indium-rich products. The optical band gaps (Eg) of the products decreased from 1.60 to 1.43 eV with variation of Cu/In molar ratio. The variation of the Urbach tail width with Cu/In molar ratio indicated that the density of the defects is much higher for the indium-rich CuInS2, which was clearly revealed from Raman measurements. 相似文献
10.
Francesca Mangiarini Adolfo Speghini Fiorenzo Vetrone 《Materials Research Bulletin》2010,45(8):927-932
In this study, monoclinic luminescent Gd2O3 nanocrystals doped with different concentrations of Er3+ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions was observed with increasing Er3+ concentration in the Gd2O3 nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er3+ concentration was increased, the intensity of the red (4F9/2 → 4I15/2) emission was observed to increase more rapidly in comparison to the green (2H11/2, 4S3/2 → 4I15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP. 相似文献
11.
Xinyu Yang Weidong Xiang Haijun Zhao Xiaojuan Liang Feifei Chen 《Materials Research Bulletin》2011,46(3):355-360
The third-order nonlinear optical properties of Bi2S3 nanocrystals doped in sodium borosilicate glass are measured by Z-scan technique. The microstructures of the glass are characterized by means of X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy, energy dispersion X-ray spectra, and high-resolution transmission electron microscopy. The results show that the Bi2S3 nanocrystals ranging from 10 to 30 nm are determined to be of the orthorhombic crystalline phase, and the third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ(3) of the glass are determined to be 2.56 × 10−16 m2 W−1, 4.13 × 10−10 mW−1, and 1.43 × 10−10 esu, respectively. 相似文献
12.
Synthesis and optical properties of L-cysteine hydrochloride-stabilized CdSe nanocrystals in a new alkali system 总被引:1,自引:0,他引:1
Feng B Teng F Tang AW Wang Y Hou YB Wang YS 《Journal of nanoscience and nanotechnology》2008,8(3):1178-1182
Water-soluble CdSe nanocrystals were synthesized in a new alkali system at lower temperatures by using L-cysteine hydrochloride as a stabilizer and Na2SeSO3 as a selenium source to enable the synthesis of CdSe nanocrystals in a wider range of pH values. The CdSe nanocrystal powder was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. We systematically investigated the effect of synthesis conditions on the optical properties of the L-cysteine hydrochloride-stabilized CdSe nanocrystals, and found that different sizes of CdSe nanocrystals can be obtained by changing the pH value, the molar ratio of L-cysteine hydrochloride to Cd2+, or the refluxing time. The emission maxima of the obtained CdSe nanocrystals can be tuned in a wider range from 477 to 575 nm by changing the pH value from 7 to 13. We observed an obvious blue-shift of the absorption and photoluminescence peak position by varying the molar ratio of L-Cys to Cd2+ from 3.5:1 to 2:1 at the same pH value. The size of the obtained nanocrystals increased and the full width at half maximum became narrower as reflux time increased. Transmission electron microscopy images indicate that the as-prepared CdSe nanocrystals have a good dispersion, which means that L-cysteine hydrochloride can control the grouping of CdSe nanocrystals excellently as a stabilizer in the new alkali system. 相似文献
13.
Synthesis and photoluminescent properties of doped ZnS nanocrystals capped by poly(vinylpyrrolidone)
Zinc sulfide semiconductor nanocrystals doped with selected transition metal ions (Mn2+, Cu2+, and Ni2+) have been synthesized via a solution-based method utilizing low dopant concentrations (0–1%) and employing poly(vinylpyrrolidone) (PVP) as a capping agent. UV/Vis absorbance spectra for all of the synthesized nanocrystals show an exitonic peak at around 310 nm, indicating that the introduction of the dopant does not influence the particle size. Calculated particle sizes for undoped and doped nanocrystals are in the 4.3 nm size range. Photoluminescence spectra recorded for undoped ZnS nanocrystals, using an excitation wavelength of 310 nm, exhibit an emission peak centered at around 460 nm. When a dopant ion is included in the synthesis, peaks in the corresponding photoluminescence spectra are red-shifted. For Mn-doped nanocrystals, an intense peak centered at approximately 590 nm is found and is seen to increase in photoluminescence intensity with an increase in dopant concentration. In contrast, for Cu-doped and Ni-doped nanocrystals, weaker peaks centered at around 520 and 500 nm, respectively, are observed and are noticed to decrease in photoluminescence intensity with an increase in dopant concentration. These results clearly show that careful control of synthetic conditions must be employed in the synthesis of doped semiconductor nanocrystals in order to obtain materials with optimized properties. 相似文献
14.
Sub-2 nm SnO2 nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties
Hui Zhang 《Materials Research Bulletin》2008,43(11):3164-3170
A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO2 nanocrystals, in which NaBH4 is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO2 nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO2 nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO2 nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO2 (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO2 nanocrystals has been preliminary presented. 相似文献
15.
Nanocrystalline CeO2 particles doped in the range of 0-20% of Ca2+, La3+, and Zr4+ have been prepared from hydrothermal synthesis of nitrate solutions at 200 °C and the influences of the dopants on microstructure and optical properties of the nanoparticles have been investigated. The unit cell parameter is found to be modified by −0.39, +0.83 and +0.16% for doping of 20% Zr4+, La3+, and Ca2+, respectively. For each batch prepared, nanoparticles with a narrow size distribution of 5-15 nm have been obtained. A high-resolution transmission electron microscopy investigation reveals that these particles are single crystals mostly having hexagonal, square or circular two-dimensional projections. UV-visible spectra of doped powders exhibit shift of the absorption edge and absorption peak with respect to those of the undoped CeO2 particles and has been attributed to compensation of Ce3+ and decreasing crystallite size as result of doping. 相似文献
16.
Jiqing Jiao 《Materials Research Bulletin》2010,45(2):181-185
Compared to conventional methods, a simple route is offered for synthesis of BaCO3 with CO2 and least energy consumption. And the morphology of BaCO3 was tuned by controlling reaction conditions. The X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) were employed to characterize the products, the results showed that the products with various morphologies had the same crystal phase and growth direction. However, the distinct difference of the prepared products were determined by Raman and UV-vis spectra, showing shape-dependent optical properties. The results provide a useful model system for investigating the shape-dependent optical properties of carbonate nanocrystals. 相似文献
17.
This article presents a systematic investigation of the optical properties and the growth process of CdTe nanocrystals during
their hot-injection-based synthesis in liquid paraffin. Cadmium(II) stearate and tributylphosphine telluride are used as precursors.
The as-obtained nanocrystals are characterized by transmission electron microscopy (TEM) with energy dispersive spectroscopy
(EDS), X-ray powder diffraction (XRD), UV–vis absorbance, and fluorescence spectroscopy. The changes in optical absorbance
and fluorescence during the nanocrystal synthesis are studied. The average nanocrystal size and the mean nanocrystal concentration
are derived from the optical spectra and their changes during the synthesis are investigated. It is found that synthesis at
lower temperature (150 °C) favors the continuous nucleation and leads to the formation of relatively smaller nanocrystals
(~3 nm in size), whereas the nanocrystal concentration is relatively constant during synthesis at higher temperature (250 °C)
thus leading to the formation of larger nanocrystals (~5 nm in size). 相似文献
18.
Preparation and characterization of zinc sulfide nanoparticles under high-gravity environment 总被引:1,自引:0,他引:1
Nanosized ZnS particles were prepared under high-gravity environment generated by the rotating packed bed reactor (RPBR) using zinc nitrate solution and hydrogen sulfide gas as raw materials. The effects of experimental conditions such as reactant concentration, reaction temperature, rotating speed of the RPBR and aging time, on the preparation of nanosized ZnS particles were investigated. A set of suitable operating parameters (the aging time of 48 h, concentration of zinc nitrate of 0.1 mol/l, reaction temperature of 45 °C and rotating speed of the RPBR of 1500-1800 rotation/min) for the preparation of nanosized ZnS were recommended. Under these optimum conditions, well-dispersed ZnS nanoparticles was obtained. The crystal structure, optical properties, size and morphology of the product were also characterized by XRD, UV-Vis spectrophotometer, and TEM, respectively. Results indicate that the prepared ZnS has a good absorption for light in the wavelength range of 200-330 nm. XRD analysis also shows the prepared ZnS is in a sphalerite crystal phase. The process has great potential of commercialization. 相似文献
19.
Colloidal CdSe nanocrystals were synthesized in reaction media consisting of tri-n-octylphosphine (TOP) without addition of other species; the single-step approach used cadmium oxide (CdO) and TOPSe as Cd and Se sources, respectively. The temporal evolution of the optical properties of the growing TOP-capped CdSe nanocrystals was monitored for a couple of hours, showing that there are two distinguishable stages of growth: an early stage (less than 5 minutes) and a later stage; the growth kinetics of the two stages is a function of the Cd-to-Se precursor molar ratios. A rational choice of 2-6Cd-to-1Se molar ratio was found, based on the temporal evolution of the photoluminescent (PL) efficiency (studied as PL intensity and sensitivity to the media of dispersion, and non-resonant Stokes shifts). For a 2Cd-to-1Se synthesis, the growth in size was slow in the early stages and became fast in the later stages; this fast-later-stage feature could be suppressed by going to a synthesis with a 4-6Cd-to-1Se mole ratio: the nanocrystals between 0.5-60 min growth time exhibit very much similar optical properties, with less than 19 nm redshift of bandgap absorption and emission occurring. Thus, the synthetic route developed here, with a rational 4-6Cd-to-1Se molar ratio, enables us to produce high-quality CdSe nanocrystals on a large-scale with a high degree of synthetic reproducibility. The insights gained facilitate a deeper understanding of the concept of what constitutes high-quality nano-crystals: high PL efficiency resulting from a low growth rate, which can be thoroughly and readily investigated by the red-shift rate of the band-gap peak positions; in addition, the insights gained help us to define a proper synthetic approach for large-scale production with high-quality product. 相似文献
20.
I. Crupi F.S. Ruggeri A. GrassoF. Ruffino G. CataniaA.M. Piro S. Di MarcoS. Mirabella F. SimoneF. Priolo 《Thin solid films》2012,520(11):4036-4040
We analyze the results of an extensive characterization study involving electrical and optical measurements carried out on hydrogenated amorphous silicon (α-Si:H) thin film materials fabricated under a wide range of deposition conditions. By adjusting the synthesis parameters, we evidenced how conductivity, activation energy, electrical transport and optical absorption of an α-Si:H layer can be modified and optimized. We analyzed the activation energy and the pre-exponential factor of the dark conductivity by varying the dopant-to-silane gas flow ratio. Optical measurements allowed to extract the absorption spectra and the optical bandgap. Additionally, we report on the temperature dependence of the activation energy to satisfy the Meyer-Neldel rule. Finally, the influence of the individual films parameters upon the final performances of a single junction pin α-Si:H have been studied. The measurements show how a more than doubled enhancement in energy conversion efficiency can be obtained in an α-Si:H solar cell with a proper selection of synthesis conditions. 相似文献