Wiadomości Chemiczne

Nanomaterials, 2004

Library of Wiadomości Chemiczne

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  1. Preparation and properties of nanostructures in glass-ceramics systems
    Grażyna Dominiak-Dzik, Witold Ryba-Romanowski, Barbara Klimesz

  2. Perovskite – a universal structure – a challenge for nanotechnolgy
    Przemysław J. Dereń i Artur Bednarkiewicz

  3. Nanocomposites and nanocrystalline materials prepared by sol-gel techniques
    Dariusz Hreniak, Wiesław Stręk

  4. Structural and Optical Properties of Nanocrystalline KGdF4:Eu3+ and NaGdF4:Eu3+ Powders Synthesised from Solution
    M. Karbowiak, A. Mech, A. Bednarkiewicz, W. Stręk, L. Kępiński

  5. Transmission Electron Microscopy of Nanomaterials
    Leszek Kępiński, Ludwina Krajczyk

  6. Spectroscopy of Nanometer-Range Media and Mixed Lanthanide LnB3L Chelates. Their Applications Perspectives
    J. Legendziewicz, J. Sokolnicki

  7. Microwave driven hydrothermal synthesis of nanocrystalline powders
    W. Łojkowski, T. Strachowski, L. Perchuć, R. Fedyk, A. Opalińska, T. Chudoba, E. Grzanka, E. Reszke, A. Presz

  8. Application of IR and Raman Spectroscopies in Studies of Nanomaterials 
    Mirosław Mączka, Jerzy Hanuza, Wiesław Stręk

  9. Selected Characterization Methods of Nanomaterials for Al2O3-ZrO2:Tb+3
    W. Miśta

  10. Synthesis, structure and optical properties of nanocrystalline gallium nitride
    Marcin Nyk, Wiesław Stręk, Jan Misiewicz, Janusz M. Jabłoński

  11. Determination of the Grain Size Distribution of nanocrystals by Powder Diffraction means
    Roman Pielaszek

  12. Preparation, microstructure and properties of soda lime silicate glasses doped with nanosized silver particles
    M Suszyńska, L. Krajczyk, M. Szmida

  13. Solvothermal synthesis of nanostructured materials
    Mirosław Zawadzki

  14. Synthesis of nanocrystalline powder phosphors and their possible applications
    E. Zych, J. Trojan-Piegza, L. Kępiński, D. Hreniak, W. Stręk

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PEROVSKITE – A UNIVERSAL STRUCTURE – A CHALLENGE FOR NANOTECHNOLGY

Przemysław J. Dereń i Artur Bednarkiewicz

Oddział Spektroskopii Optycznej, Instytut Niskich Temperatur i Badań Strukturalnych PAN, P Nr 1410, 50-950 Wrocław 2.
E-mail: deren@int.pan.wroc.pl


The article presents properties of several crystals, the common feature of which is the perovskite structure. It was shown that electrical, magnetic and optical properties as well as their capabilities to be used as sensors, electrodes, and electrolytes in the fuel cells are direct consequence of the structure. Perovskite consists of two cations A and B, where cation A is larger than B, and of an anion O - usually oxygen. Simple structure of perovskite is described as a cube, where cations A are placed in the cube corners, oxygen ions in the middle of the cube’s faces, and cation B in the centre of the cube.

Introduction of the impurity into the structure and/or variation of the external parameters, such as pressure, temperature, electric and magnetic field, could easily modify physical properties of the perovskite. Sometimes small changes result in strong response; for example, temperature changes alter the optical transmission or transport properties.

In the present work, electrical properties of BaTiO3 and BaPb1-xBixO3 and superconducting properties of perovskites of Ba-La-Cu-O type, magnetic properties of Pb1-xLaxTi1-yZryO3 and LaMnO3, optical properties of LiNbO3, YAlO3 and LaAlO3 have been described. Additionally it has been shown the possible application of these perovskite as sensors.

As a conclusion it is proposed to investigate not only single crystals, but also nanocrystalline materials. If the perovskite’s properties are so sensitive to external conditions it could be anticipated that nanocrystals not limited by rigid huge lattice will demonstrate new properties.

Theoretical investigations of perovskite properties are a challenge as well; understanding the relationship between optical and structural properties will be the first step towards conscious design of new optical materials.


Wiadomości Chemiczne, 2004, Nanomaterials. 21.
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PREPARATION AND PROPERTIES OF NANOSTRUCTURES IN GLASS-CERAMICS SYSTEMS

Grażyna Dominiak-Dzik*, Witold Ryba-Romanowski*, Barbara Klimesz**

*Instytut Niskich Temperatur i Badań Strukturalnych PAN, ul. Okólna 2, 50-422 Wrocław.
E-mail: dzik@int.pan.wroc.pl
**Politechnika Opolska, ul. Ozimska 75, 45-370 Opole


Oxyfluoride glasses have created much interest as host material for active optical devices. After a thermal treatment close to the crystallisation temperature it is possible to obtained a glass-ceramics, in which fluoride nanocrystals are embedded in a primarily oxide glass matrix. Thus, the transparent glass ceramics represent a unique class of materials, which combine the optical advantages of a fluoride host with the mechanical advantages of oxide glass [1–7]. Glasses with composition 50GeO2-(50-y)PbO-yPbF2 (y=<15% mol) containing Pr3+ or Tm3+ ions were melted from commercial raw materials in normal atmosphere. Based on the results of differential thermal analysis DTA, glass transition temperatures and oxide glass crystallisation temperatures were derived. The as-melted glass samples were thermally treated in order to achieve controlled precipitation of PbF2 changing rare earth surrounding from oxide to fluoride. Formation of the glass-ceramics was monitored with the aid of DTA, TEM and XRD measurements. Analysis of the X-ray peak widths, with the Scherrer formula [8], gave the mean crystal size of 28 nm.

The effect of thermal treatment on optical spectra and relaxation of excited levels within the 4fn configurations of praseodymium and thulium was studied. The numerous Stark components and the reduction of inhomogeneous linewidth due to the crystalline environment were observed in heat-treated samples. Non-exponential decay curves of luminescence in as-melted glasses became nearly exponential and corresponding lifetimes longer in glass-ceramics.


Wiadomości Chemiczne, 2004, Nanomaterials. 33.
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NANOCOMPOSITES AND NANOCRYSTALLINE MATERIALS PREPARED BY SOL-GEL TECHNIQUES

Dariusz Hreniak, Wiesław Stręk

Oddział Spektroskopii Optycznej, Instytut Niskich Temperatur i Badań Strukturalnych PAN, P Nr 1410, 50-950 Wrocław 2.
E-mail hreniak@int.pan.wroc.pl


Development of new technologies for high-resolution displays and low-voltage electroluminescence devices needs applying still a smaller and smaller particles of luminescent materials. Classic methods of preparation of luminescence materials, first of all the solid state reaction, provide inorganic polycrystalline efficient luminophores with a narrow distribution of particles size from range of micrometers [1, 2]. On the other hand, it is well known that their sizes should be of nanometric scale. From this reason new methods of preparation of nanoluminophores were recently strongly developed. Nevertheless, it is important to know that both amorphous as defected materials are characterized by increasing the number of crystallographic positions of activator ion leading directly to decrease of efficiency and monochromaticity of emission [3, 4]. Therefore it is important to retain a high degree of crystallization of materials and the lowest possible concentration of defects in nanosized particles of luminophores. For this purpose new low-temperature techniques of preparation well-defined nanocrystals have been created and improved [5–12]. At the present time, the best known and popular methods of obtaining the applicable nanomaterials are thin film deposition techniques. In this case the final properties of fabricated materials are determined in the first stage of synthesis of nanocrystals. Intensively investigated and very interesting are also organic and inorganic composites where nanocrystals are introduced and immobilized in glass or polymer matrices. These nanocomposites can be synthesized in situ (i.e. in porous sol-gel glass or in polymer) [18, 19] or prepared from obtained earlier nanocrystals, dispersed in liquid medium and introduced into matrices before their solidification [17, 20]. Very promising are also the so-called nanoceramics composed of nanosized grains. Due to specific properties of these materials they are very interesting not only for luminescence devices but also for designing a new generation of fuel cells. Unfortunately, the main disadvantage of nanoceramics is the difficulty of their fabrication. During a conventional annealing process the crystalline grains undergo a spontaneous increase of their sizes from nanometer to micrometer range. For this reason new, still enhanced techniques of preparation of nanoceramics are developed [21, 22].


Wiadomości Chemiczne, 2004, Nanomaterials. 47.
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STRUCTURAL AND OPTICAL PROPERTIES OF NANOCRYSTALLINE KGDF4:EU3+ AND NAGDF4:EU3+ POWDERS SYNTHESISED FROM SOLUTION

M. Karbowiaka, A. Mecha, A. Bednarkiewiczb, W. Strękb, L. Kępińskib

a Wydział Chemii, Uniwersytet Wrocławski, ul. F. Joliot-Curie 14, 50-383 Wrocław
b Instytut Niskich Temperatur i Badań Strukturalnych PAN, ul. Okólna 2, 50-422 Wrocław


The luminescence spectroscopy of rare-earth (RE) ions in the vacuum ultraviolet (VUV) spectral range has attracted a considerable attention in the past few years. This results from the search for new efficient VUV-excited phosphors for mercury-free fluorescent lamps and plasma display panels [1,2]. Optimisation of synthesis procedure is of great importance for quantum efficiency, since energy migration to lattice traps may degrade strongly the optical performance of the phosphor. Elimination of non-radiative losses by improvement of material synthesis can result in a visible quantum efficiency of 200% [3–5]. Therefore, the spectroscopic properties of fluorides of different composition and synthesised by different methods should be tested to optimise the quantum efficiency. A solid state (SS) reaction conducted at temperatures of ~650°C is commonly used for synthesis of complex fluorides in a powder form. However, this process requires strictly inert or even reactive gas atmosphere, since the elevated temperature promotes strongly the migration of O2- and OH- ions into the fluoride lattice, which may result in formation of oxygen-rare-earth ion aggregates, degrading seriously the quantum efficiency of the material. An alternative method for synthesis of fluorides is a co-precipitation from solution. This method allows for better control of morphology and homogeneity of obtained materials and limits strongly the oxygen contamination in obtained compounds [6]. Moreover, this method, in contrast to solid state reaction, allows to obtain the nanosized powders.

For testing the influence of a fluoride composition and a method of synthesis on structural and optical properties of material, the KGdF4:Eu3+ and NaGdF4:Eu3+ powders were synthesised by the wet chemistry routes. The first part of this paper is focused on investigation of behaviour of the KGdF4:Eu3+ powdered batches, initially characterised by 20 and 25 nm average crystallite size, versus thermal treatment. The second part is devoted to the comparison of structural and luminescent properties of NaGdF4:Eu3+ synthesised from solution by three different methods.

The single phase KGdF4:Eu3+, with the “frozen” fluorite type of crystal structure precipitates from solution (Fig. 2a and 3a). This differentiates coprecipitation technique (CP) from solid-state reaction or hydrothermal synthesis, since both these methods yield the orthorhombic KGdF4 (Fig. 5). Powders with average grain size of 25 (Eu:KGF(I) sample) or 20 nm (Eu:KGF(II) sample) (Table 1 and Fig. 2 and 3) could be obtained by changing the duration of ageing in mother solution. The crystallite size determined from XRD analysis (Fig. 2 and 3) corresponds well to that determined from TEM measurements (Fig. 4). The XRD pattern could be indexed on the basis of a cubic cell, space group Fm3m , with a = 5.746(5) Å

There are significant differences in behaviour of these two powdered batches, characterised by different crystallite sizes, versus thermal treatment in 300–790°C temperature range, as has been shown by X-ray powder diffraction (Fig. 2 and 3), termogravimetric (Fig. 7), infrared transmission spectroscopy (Fig. 8 and 9) and emission spectroscopy methods (Fig. 10).

At elevated temperature both investigated samples undergo the phase transitions, first from cubic to orthorhombic (Pnma, a = 6.130(1), b = 3.654(1) and c = 15.423(1) Å), then to trigonal (P31, a = 14.175 (6) and c = 10.123 (1) Å) and finally to high temperature cubic modifications of KGdF4 (Fig. 2 and 3). At given temperature, the abundance of particular polymorph depends on initial crystallite sizes of powder, but for both samples the highest concentration of orthorhombic and trigonal form was observed at ~550 and 650°C, respectively.

IR spectra (Fig. 8) show, that most of the water molecules are adsorbed at the surface of the material, and that water is stronger bounded for sample, which has been aged longer in solution, in spite of larger crystallites and smaller surface/grain volume ratio. Heating at temperatures of 790°C is indispensable for total removal of hydroxyl groups. The SF6 proved to be efficient agent for removing of hydroxyl groups from fluoride material (Fig. 9), and additionally it limits the formation of fluoride deficiency defects in host lattice. Sample with smaller crystallite size is significantly more susceptible to reduction of Eu3+ to the divalent state (Fig. 10).

NaGdF4:Eu3+ has been precipitated from solution by three different methods. Both co-precipitation (CP) and reversed-micelle methods (RM) yields powders with average crystallite size of 7 nm (Fig. 12 and 13, Table 2), whereas monocrystallites with size of the order of micrometers (Fig. 15c) could be obtained as result of reaction of solid GdF3 with NaF solution (SR method). The hexagonal form of NaGdF4 is stable in the 20–750°C temperature range, which allows for tuning of the crystallite size in 7 nm – ~1 mm range by changing the duration and temperature of heat treatment (Fig. 12, Table 12). Powders obtained by RM method contain larger amount of surface bounded water compared to CP samples, but the water may be removed at lower temperature (50-260°C) (Fig. 17). For coarse crystalline SR sample only traces of adsorbed water could be detected (Fig. 18). In the case of Eu3+ doped NaGdF4 samples, the 5D1,2,3f5D0 emission integral intensity ratio may be treated as a measure of number of OH- groups incorporated into fluoride lattice (Fig. 20, 21 and 22). For Eu:NGF-CP680 sample (heated at 680°C) and Eu:NGF-SS sample this ratio has a very similar value, which indicates, that independently on the method of synthesis, a CP technique followed by a heat treatment or a SS reaction, phosphors with only vestigial amounts of the hydroxyl groups incorporated into the lattice may be obtained (Fig. 16 and 20). Energy transfer from Gd3+ to Eu3+ ions is most efficient for Eu:NGF-RM680 sample, whereas for Eu:NGF-SR680 sample the highest rate of non-radiative relaxation of excited Gd3+ levels is observed.


Wiadomości Chemiczne, 2004, Nanomaterials. 63.
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TRANSMISSION ELECTRON MICROSCOPY OF NANOMATERIALS

Leszek Kępiński*, Ludwina Krajczyk

Oddział Chemii Nanomateriałów i Katalizy, Instytut Niskich Temperatur i Badań Strukturalnych PAN, ul. Okólna 2, 50-422 Wrocław.
*E-mail: kepinski@int.pan.wroc.pl


Transmission Electron Microscopy (TEM) and its modern mutation High Resolution Transmission Electron Microscopy (HRTEM) is one of the most important methods in nanomaterials investigations. The principal reason is its high spatial resolution (below 0.2 nm) but also universality, i.e., ability of observation of both images and diffraction patterns of individual nanometer size objects. In particular, TEM provides fundamental information on morphology and microstructure of the sample including [1]:

  1. identification of phases present
  2. spatial distribution of the phases
  3. shape and size distribution of particles
  4. atom ordering (crystal structure).

In the present contribution we shortly describe modern TEM techniques applied to solving above mentioned problems and then we give examples of studies of nanomaterials performed in the Electron Microscopy Laboratory of the Institute of Low Temperature and Structure Research, Polish Academy of Science in Wrocław. Nanomaterials investigated in our group involve supported catalysts [15–22], oxide phases dispersed in/on oxide matrices [23–27], lanthanide oxide nanopowders [28–30], metal nanoparticles in silica glasses [38–43] and thin metal films evaporated on inorganic supports [44–45].


Wiadomości Chemiczne, 2004, Nanomaterials. 101.
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SPECTROSCOPY OF NANOMETER-RANGE MEDIA AND MIXED LANTHANIDE Lnb3L CHELATES. THEIR APPLICATIONS PERSPECTIVES

J. Legendziewicz*, J. Sokolnicki

Wydział Chemii Uniwersytetu Wrocławskiego, ul. Joliot-Curie 14, 50-383 Wrocław
*jl@wchuwr.chem.uni.wroc.pl


To obtain cathode-ray pumped powder lasers for high resolution monochromatic displays, it is important to produce low density scattering media for optically pumped lasers with sufficiently low generation threshold and relatively small volume of the excited medium involved in generation of light [1-8]. The main objective of the paper is focused on the characterization of the physical properties and the methods of synthesis of nanosize systems incorporated in silica gel and glasses [9, 10, 12]. Morphology and types of the nanosize seeds created in gels and silica glasses were determined basing on X-ray diffraction (XRD), transmission electron microscope (TEM) and spectroscopic methods [9, 10, 12, 15, 16, 21] The spectroscopic behavior in the temperature range of 293 – 4K and efficiency of the emission of nanometer scattering ceramics doped with Nd(III) ions will be discussed. Excited state dynamics will be analyzed and applicability of the obtained ceramics will be proposed [9, 10, 12]. On the other hand, the compounds basically similar to those used as recursors in creation of nanometer systems can be used in organic layered electroluminescent diodes (OLEDs) [10, 14, 16, 21, 24, 25, 29-31].The important characteristics of these materials can be correlated with the donor-acceptor properties of the substituents in the ligands. Moreover, these donor-acceptor properties are responsible for location of energy levels, efficiency of energy transfer, electron-phonon coupling and finally quantum yield of luminescence. Two new types of lanthanide mixed b-diketones will be characterized and their possible application in OLEDs basing on spectroscopic data will be analyzed [10, 29, 30]. The theoretical model for energy transfer as well as the calculation of the quantum yields for different mechanisms are described [26, 32]. The appropriate selection rules are discussed [26, 32, 33]. The most probable channels of energy transfer in the system under consideration are determined.


Wiadomości Chemiczne, 2004, Nanomaterials. 125.
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MICROWAVE DRIVEN HYDROTHERMAL SYNTHESIS OF NANOCRYSTALLINE POWDERS

W. Łojkowski1, T. Strachowski1,2, L. Perchuć1, R. Fedyk 1,2, A. Opalińska1,2, T. Chudoba1, E. Grzanka1,4 , E. Reszke3, A. Presz1

1Centrum Badań Wysokociśnieniowych Polskiej Akademii Nauk, „Unipress” ul. Sokołowska 29/37, Warszawa
2Wydział Inżynierii Materiałowej PW, ul. Wołoska 141, Warszawa
3Ertec Poland, ul. Rogowska 146/5, Wrocław
4Wydział Fizyki UW, ul. Hoża 69, Warszawa


The aim of this work was to synthesise nanocrystalline materials by using the microwave (MW) driven hydrothermal reaction. The main advantage of this method is the reaction rate, which is distinctly higher than in the case of conventional heating.

Powders of ZrO2 containing 0,5–10 mol% of praseodymium(III) was obtained by adding the praseodymium nitrate to an aqueous solution (0,5 M) of ZrOCl2. The solution was neutralised with NaOH to the pH value equal 10. Pressure up to 8 GPa was used during the MV driven reaction. It has been found that the grain size and the amount of the monoclinic phase of ZrO2 increase with the increase of the pressure. Moreover, the grain size of zirconia affects the luminescence intensity of the nanocrystalline material.

Zinc oxide nanopowders were prepared from a 0,1 M solution of zinc chloride neutralised with NaOH to the pH value equal 10 or with urea and trietanolamine used in the MW reactor and during resistance or conventional heating. Pressures up to 1 MPa have been used during the MW driven hydrothermal process. The grain size of the obtained ZnO nanopowder ranged from 10 to 65 nm. Particles of different size and morphology have been obtained by using different reagents and different heating procedures.

Iron oxide nanopowders have been prepared starting from ferric chloride, ferrous sulphate and urea solutions. Pure hematite, maghemite and magnetite were obtained in the MW reactor under hydrothermal conditions. Doping the nanopowders with cobalt ions has induced magnetic properties of iron oxide

The obtained nanopowdered materials were characterised by X-ray diffraction, by the scanning electron microscopy and the BET system.


Wiadomości Chemiczne, 2004, Nanomaterials. 139
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APPLICATION OF IR AND RAMAN SPECTROSCOPIES IN STUDIES OF NANOMATERIALS 

Mirosław Mączka1, Jerzy Hanuza1,2 Wiesław Stręk1

1  Instytut Niskich Temperatur i Badań Strukturalnych PAN we Wrocławiu
2  Katedra Chemii Bioorganicznej Akademii Ekonomicznej we Wrocławiu, Wydział Inżynieryjno-Ekonomiczny


The paper discuss application of the Raman and IR spectroscopy in studies of the nanomaterials. The basic differences between phonon properties of bulk and nanomaterials are discussed. Based on references [1-8] the main effects characteristic for the nanomaterials, their origin and influence on the phonon properties are summarized. This short review shows that the Raman and IR techniques are valuable tools in nanomaterials studies but the analysis of the spectra requires the knowledge of many parameters which need to be evaluated by other experimental techniques.


Wiadomości Chemiczne, 2004, Nanomaterials, 159.
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SELECTED CHARACTERIZATION METHODS OF NANOMATERIALS FOR Al2O3-ZrO2:Tb+3

W. Miśta

Instytut Niskich Temperatur i Badań Strukturalnych PAN, ul. Okólna 2, 50-950 Wrocław,


This paper provides an overview of the experimental techniques used to characterize nanomaterials, especially some kind of thermo-analytical methods like temperature-programmed reaction (TPR, TPD-MS), thermogravimetry combined with mass spectrometry (TG-EGA-MS) and also textural analysis using N2 adsorption. The utilization of these experimental techniques for characterization of Al2O3-ZrO2:Tb+3 nanomaterial is shown. The chemical adsorption isotherm yields information about the active surface of a material and has been employed for many years as a standard analytical tool for the evaluation of heterogeneous catalysts. Temperature-programmed reaction techniques have emerged from the 1950’s as indispensable companion to the chemisorption isotherm analyses in many areas of industry and research. Optimum design and efficient utilization of catalysts require a thorough understanding of the surface structure and surface chemistry of the catalytic material. Nitrogen (at 77K) is the most widly used adsorptive for the characterization of porous materials. Although the Brunauer-Emmett-Teller (BET) theory is based on an over-simplified model of the multilayer adsorption, the BET method continues to be used as a standard procedure for determination of the specific surface area. The basic principle in TG is to measure the mass of a sample as a function of temperature. This, in principle, simple measurement is an important and powerful tool in solid state chemistry and materials science. The method, for example, can be used to determine the crystallization water, to follow the degradation of materials, to determine reaction kinetics, to study oxidation and reduction, or to teach the principles of stoichiometry, formulae and analysis. Thermogravimetry is a limited technique as it cannot distinguish the actual nature of the material evolved in the course of the process and is seldom able to describe completely the process under study. It is also handicapped in resolving overlapped thermal events. However, a TG-EGA-MS technique, which can provide (by mass spectrometry) additional information on the nature and content of the liberated gases during thermal treatment, will be able to describe the process more precisely. This technique is also now used for materials processing, particularly for synthesis of nanocrystalline materials.


Wiadomości Chemiczne, 2004, Nanomaterials, 167.
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SYNTHESIS, STRUCTURE AND OPTICAL PROPERTIES OF NANOCRYSTALLINE GALLIUM NITRIDE

Marcin Nyk1, Wiesław Stręk2, Jan Misiewicz1, Janusz M. Jabłoński2

1Instytut Fizyki Politechniki Wrocławskiej, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław.
E-mail: marcin.nyk@pwr.wroc.pl 2 Instytut Niskich Temperatur i Badań Strukturalnych PAN, P Nr 1410, 50-950 Wrocław 2. Wrocław


In the first section the, synthesis, structural characterization, photoluminescence and cathodoluminescence properties of nanocrystalline GaN, embedded in silica sol-gel glass have been described [13–15]. Transmission electron microscopy techniques (TEM, HRTEM, and SAED) and X-ray diffraction were used for characterization of the structure, phase composition and morphology of the xerogel composite. Depending on the nitration temperature the GaN, semiconductor materials with average nanocrystallite sizes ranging from 4–5 nm up to about 10 nm were prepared by the sol-gel technique. The origin of a weak blue band luminescence localized at 355 nm is associated with the band gap of semiconductor at 3.4 eV. The dominating yellow luminescence band centered at 545 nm is due to the lattice defects.

The second part concerns the synthesis and microstructure investigations of Eu3+, Tb3+ doped and undoped GaN nanocrystallite powders. The Raman, reflection, photoluminescence and cathodoluminescence spectra were measured. It was found that the GaN nanocrystallites exhibit the broad band luminescence with a maximum in the red spectral range [19–22].


Wiadomości Chemiczne, 2004, Nanomaterials, 179.
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DETERMINATION OF THE GRAIN SIZE DISTRIBUTION OF NANOCRYSTALS BY POWDER DIFFRACTION MEANS

Roman Pielaszek

Centrum Badań Wysokociśnieniowych PAN, ul. Sokołowska 29/37, 01-142 Warszawa


One of most general diffraction laws, the Debye equation, is rewritten for the special case of crystalline diffracting matter. The Debye formula for crystals obtained has two components: structural and microstructural (diffraction line position and profile).

An analytical expression for the diffraction line profile for polydispersive powders (particularly, nanopowders) with Gamma Grain Size Distribution (GSD) is derived. The expression consists of elementary functions only and can readily replace standard functions (like Gaussian, Lorentzian or Pearson) for diffraction peak fitting purposes. This allows for direct Grain Size Distribution determination using standard fitting software.

An example of GSD evaluation is presented. It is shown that entire GSD may be determined by fitting of a single diffraction line with a physically meaningful function.

Well established Scherrer method allows for determination of the average grain size of a crystalline powder by measurement of Full Width at Half Maximum (FWHM) of the diffraction peak profile. We propose an enhancement of this classical method. Measurement of two widths of the same peak, allows for two parameters to be distinguished: the average grain size and dispersion of sizes s. These parameters are sufficient to draw Grain Size Distribution (GSD) curve, that is much more informative than a single size parameter .

We propose to measure widths at 1/5 and 4/5 of the peak maximum (FW1/5M and FW/4/5M, respectively). A simple algebraic formula that converts measured FW4/5M and FW4/5M values into and s is presented. The FW1/5 / 4/5M method proposed in this paper is especially sensitive in case of a broad diffraction maxima, i.e. for nano-sized polycrystals.


Wiadomości Chemiczne, 2004, Nanomaterials, 199.
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PREPARATION, MICROSTRUCTURE AND PROPERTIES OF SODA LIME SILICATE GLASSES DOPED WITH NANOSIZED SILVER PARTICLES

M Suszyńska, L. Krajczyk, M. Szmida

Instytut Niskich Temperatur i Badań Strukturalnych PAN, 50-950 Wrocław 2


There is a considerable interest in oxide glasses containing nanosized metal particles because many of their properties are driven by the peculiar behavior of the quantum dots. The extraordinarily strong polarisability of the metal clusters at the surface plasmon frequency results in marked non-linear optical susceptibility and a picosecond response time at high excitation intensities which are comparable with that characteristic of crystalline materials [1–4]

Our previous investigations of commercial multicomponent soda lime silicate glasses (SLSG), containing silver colloids, have shown that optical, dielectric, and mechanical characteristics of such materials are strongly affected by both the microstructure of the glassy matrix and the peculiar behavior of the silver nanoparticles [10, 33]. While such property changes are important in their own right, especially from a materials technology viewpoint, a more thorough documentation of the extent to which they occur may provide additional understanding of the processes of amorphous phase separation itself. Moreover, it is of fundamental importance to develop processes that allow controlling the size, shape, concentration and distribution of the metal clusters inside the glassy matrix.

To obtain a deeper insight into the processes, which may control the mentioned phenomena, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analysis have been performed for commercial SLSG. The microstructure of the specimens was modified by chemical (ion - exchange with silver), thermal (high temperature annealing in air and hydrogen) and mechanical (tensile stretching) treatments. Hydrogen and irradiation were used to change the number of reduced silver, while plastic deformation has altered the shape and distribution of the microstructure elements.

TEM – observations were accompanied by the measurements of optical absorption (OA), microspectrophotometry, thermally stimulated depolarization currents (TSDC), microhardness (VH and UHmax) and the crack - formation resistance (Pc).

It has been stated that:
Intense phase separation is present yet in the as prepared specimens, and the separated Na2O - rich phase appears in the form of more or less spherical droplets.
During annealing in air at 873 K or nitrogen at 673 K, the droplets grow in size and show secondary phase separation phenomena, while silver ions became reduced to the atomic form which give rise (due to Ostwald ripening) to small precipitates of colloidal silver.
The spherical nanosized silver particles induce stable yellow - brownish coloration of the exchanged and annealed and/or irradiated specimens.
Plastic deformation of the exchanged specimens results in shape changes of both the matrix droplets and the silver nanoparticles as well. The spherical silver particles became transformed into prolate spheroids (oriented in the tensile direction), which induce birefringence and dichroism of the system; these effects could be potentially exploited in the production of colored polarizes and liquid crystalline displays; cp. Fig.13.
The presence of silver induces relatively small compressive stresses in the near – surface layers of the exchanged specimens; these stresses are responsible for some improvement of the mechanical characteristics of the material. The Vickers microhardness and the crack formation resistance can be understood by taking into account not only the geometry of the exchanging ions, but also the electronic polarizability of silver which allows an easier fit of these ions into the glass network. This behavior gives rise to their weak interactions with the nonbridging oxygens and small distortions of the matrix. Under these conditions, the fracture mechanics models are probably not strictly applicable for the investigated system.
The method of thermally stimulated depolarization currents could be effectively exploited in studies of the kinetics of phase separation from the early beginning of the process. Moreover, the joint effect of colloidal silver and the applied electric field results in partial transformation of the amorphous droplets into crystalline Na2O particles.
Ionizing radiation induces formation of the interconnected structures and a partial devitrification of the amorphous matrix. The irradiation is also effective in reduction of ionic silver to the form of nanosized metal particles, which show a narrow size distribution; see Fig.11; this effect could be important for waveguiding characteristics of the studied material.


Wiadomości Chemiczne, 2004, Nanomaterials, 235.
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SOLVOTHERMAL SYNTHESIS OF NANOSTRUCTURED MATERIALS

Mirosław Zawadzki

Instytut Niskich Temperatur i Badań Strukturalnych PAN, Ul. Okólna 2, 50-950 Wrocław
e-mail:zawadzki@int.pan.wroc.pl


The preparation of nanoparticles well defined in size and morphology is an important challenge for various industrial applications including: finely divided pure oxides with high reactivity, precursors of fine ceramics, abrasive powders, optical or magnetic pigments, catalysts etc. [1–5]. Solvothermal method is a powerful route for the preparation of such materials. In this method, nanophase materials are produced by chemical reactions in an aqueous or organic solution under the simultaneous application of heat and pressure in the presence of an alkali or acid that has a pseudo-catalytic effect upon the reaction [6–8]. A number of fundamental properties of solvelts are greatly affected by pressure and temperature, for example, the viscosity or dielectric constant are considerably reduced; this have major impli-cations on the solubility of solid reagents under reaction conditions. Synthesis under solvothermal conditions offers some significant advantages over other chemical synthesis techniques. First, it is easy to control particle size and morphology by varing the synthesis conditions (temperature, pressure, time, concentration, pH, shearing forces, nature of additives). Secondly, many nanomaterials can be directly synthesised (one step synthesis) in the desired crystalline phase at relatively low temperature. Understanding the solvothermal crystallization of inorganic solids is very difficult but two distinct reactions mechanisms are always considered: in situ heterogeneous reaction mechanism and homogeneous dissolution-precipitation mechanism [16]. Solvothermal process open a fruitful route for improving the synthesis of well known nanomaterials, furthermore, allow the preparation of nanophase materials which are difficult or impossible to obtain by other methods.


Wiadomości Chemiczne, 2004, Nanomaterials, 263.
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Synthesis of nanocrystalline powder phosphors and their possible applications

*E. Zycha, J. Trojan-Piegzaa, L. Kępińskib, D. Hreniakb, W. Strękb

aWydział Chemii, Uniwersytet Wrocławski, 50-383 Wrocław, Ul. F. Joliot-Curie 14.
*E-mail: zych@wchuwr.chem.uni.wroc.pl
bInstytut Niskich Temperatur i Badań Strukturalnych PAN, Wrocław, Ul. Okólna 2


In this paper we discuss various physical forms of powder luminescent materials utilized in practical applications. These are single crystals, glasses, powders and sintered ceramics. We concentrate on powders and consider the present trend in the research to develop synthesis procedures for fabrication of high-efficiency luminescent materials consisting of nanocrystalline particles. We consider how the shape of the particles influences the packing efficiency of powders for screen creation. We show that spherical particles are the most attractive for making various screens since they pack most effectively giving the most dense powder layer on the screen. Subsequently, we consider four different synthesis techniques producing nanocrystalline powders of Lu2O3 based phosphors. Two of these procedures are based on combustion of lutetium nitrate with urea or glycine. TEM images of the two products show that the combustion with urea produced a strongly agglomerated powder while combustion with glycine ended with a fluffy powder of minor agglomeration only. Third technique we examined for making lutetia-based phosphors is the Pechini process, in which the citric acid and glycol forms polymer net incorporating the metal ions into it. The subsequent combustion of the organic net at 650ºC create crystalline Lu2O3. Finally, we tested the homogeneous precipitation of Lu(OH)3 with urea at 70-80ºC. The hydroxide could be easily decomposed to Lu2O3 by heating at 650ºC. Such obtained powders were the least agglomerated ones and what is more they were build up of perfectly spherical particles of the same size of about 130 nm. Thus the homogeneous precipitation proved to be the very promising procedure for fabrication of nanocrystallne non-agglomeratged powder phosphors.


Wiadomości Chemiczne, 2004, Nanomaterials, 277.
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