Hydroxyl Impurities Research Articles

Investigation of uniformity in fused quartz crucibles for Czochralski silicon ingots

As there is an increased demand for monocrystalline silicon based solar cells, there is an increased interest in stronger and more durable fused quartz crucibles used in the Czochralski process. In this study we focused on the uniformity of hydroxyl impurities in these crucibles, and its potential influence on viscosity of the crucible by combining data from IR-microscopy and a self-made viscosity measurement setup. A half of a fused quartz crucible manufactured from two types of sands was studied, the OH groups content was mapped, and the viscosity at 1500 °C was measured. Local variations in the OH groups content of on average 26.7 ppm difference between the top and the bottom of the crucible were detected. The viscosity measurements further confirmed the crucible’s inhomogeneity as no clear trends or direct correlations to the OH groups content were observed. The correlation between the different sand types used for crucible manufacturing and the OH groups content was also investigated in four samples originating from four different crucibles. Two different trends in the OH groups distribution were found: while two of the studied crucibles showed an increased OH groups content in the boundary between the bubble free and the bubble containing layer, the other two showed an increased and maximum OH groups content in the bubble containing layer, and the link between the sand types and the OH groups content was confirmed. The source of the local inhomogeneities and the two different trends of OH groups distribution can possibly be attributed to the sand quality, the sand particle size, and the difference in the manufacturing process, such as thermal history or distribution of sand.

Cooperative sensitization upconversion of ex-situ sol-gel synthesized ZnO-SiO2: Nd3+/Yb3+ dense glass ceramic material under 980nm laser pumping

Herein, we use a modified ex-situ sol-gel synthesis route to prepare Zinc-Silicate (ZnO-SiO2:Nd3+/Yb3+) dense glass ceramic material. The Judd-Ofelt parameters were estimated from absorption spectra of the ZnO-SiO2:Nd3+/Yb3+ material. Upconversion luminescence (UCL) in the material was achieved due to the sensitization of Yb3+ ions through 980 nm diode laser excitation along with CIE 1931 chromaticity diagram to analyze the white light emission. PL confocal microscopy was used to confirm the spatially resolved PL of the material. Thus, the as-synthesized material demonstrates its viability by producing white luminescence across its surface when excited by a 980 nm diode laser, which could find potential applications in various photonic applications. TEM-EDS mapping of material was performed to visualize elemental doping of the material. The structural characterization of the material was studied with X-ray diffraction (XRD) analysis and FTIR spectroscopy to report invariance of ZnO-SiO2 host. The thorough removal of hydroxyl impurity (-OH) and the pyrolysis of zinc alkoxides were confirmed through thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis.

Removal of hydroxyl impurities in vein quartz by vacuum roasting

Removing hydroxyl impurities is the key to preparing high-purity quartz sand by replacing natural crystals with vein quartz. Water hydroxyl groups in inclusions (WHI) and Silanols groups in the crystal structure (SHCS) are the two main types of hydroxyl impurities. In this study, a vacuum roasting technique was used to eliminate volatile WHI and SHCS impurities from quartz. The mechanisms by which vacuum roasting accelerated the crystal transformation to remove WHIs and the intrinsic mechanism of vacuum roasting that promoted the diffusion of water to remove the SHCS were revealed. The results showed that under the same experimental conditions, the hydroxyl content in quartz decreased from 226.8 μg g−1 to 172.2 μg g−1 after atmospheric pressure roasting. It further decreased to 88.2 μg g−1 after vacuum roasting, satisfying the hydroxyl content requirement of high-purity quartz used for quartz crucibles. This study makes it possible to prepare high-purity quartz sand from vein quartz, which is important for the development of photovoltaics.

Structural and morphological characterizations of ex-situ sol-gel derived luminescent Nd3+-Yb3+ion co-doped zinc-silicate dense glass-ceramic

We proposed a novel ex-situ sol-gel synthesis of Nd3+ (0.7 mol%) and Yb3+ (X; X = 0.0, 0.7, 1.5, 3.0 mol%) ion co-doped Zinc-Silicate (SZNYX) dense glass-ceramic(DGC) samples. The structural analyses of the SZNY07-DGC sample were performed at different annealing temperatures using X-ray diffraction (XRD) analysis and Fourier transforms infrared (FTIR) spectroscopy. The tetragonal willemite Zn2SiO4 structure with an R-3(148) space group was confirmed from XRD results. The formation of the pure oxide phases (bridging oxygen) was noticed at FTIR spectra with the complete removal of hydroxyl impurity at higher annealing temperatures. The presence of ZnO crystallites with the inter-planer spacing of ⁓ 0.28 nm and Nd3+/Yb3+ ion pair in an amorphous silica host was confirmed via transmission electron microscopy (TEM) and TEM-energy dispersive spectroscopy (EDS) respectively. The white up-conversion luminescence (UCL) under a 980 nm excitation was attributed to the simultaneous emission of wavelength in the visible spectrum. The intensity of UCL was initially rising with an increase in Yb3+ ion concentration whereas the optimized luminescence was obtained for samples with 1.5 mol% Yb3+ ion concentration. The CIE chromaticity coordinates (0.34, 0.35) of corresponding UCL spectra were invariant with the change in Yb3+ ion concentration. The photoluminescence (PL) confocal mapping of the SZNY15-DGC sample was performed at different locations under a 980 nm laser excitation source which turned out non-uniform in nature throughout the surface. Thus as-synthesized SZNYX-DGC samples have spectacular upconversion luminescence for near-infrared excitation which may be utilized in thermal sensing, photovoltaic, displays, and photonic devices.

Radiation and Emission Phenomena in Combination

Radiation and Emission Phenomena in Combination

Influence of Neutron Irradiation Conditions on Maximal Frequency of IR Absorption Spectra of LiF:OH Single Crystal

For many solids operating under irradiation conditions, the study of their behavior at the neutron irradiation is of importance. Herein, the influence of neutron irradiation conditions on the infrared (IR) absorption spectra of LiF crystals containing different amounts of hydroxyl and metallic impurities is considered. The investigations are carried out for discovering new peculiarities under the extreme irradiation conditions of LiF—being a very important material for practical applications. In the crystals with OH− impurity after the action of neutron irradiation, quite clear bands are appeared in the region of 1900–2200 cm−1. The delivered doses vary from 1014 to 3 × 1017nnvt. LiF crystals are investigated by differing both in qualitative and quantitative contents of OH− ions. With the increase in irradiation dose, the maximum IR absorption of all investigated groups of crystals shifts to the region of low energies. The appearance of a new band in the IR spectrum and its shift as a function of dose is associated with the radiolysis of OH− molecule.

Effect of draw temperature and flame polishing on birefringence of silica glass fiber

AbstractRecently developed methods for high resolution birefringence measurement have been applied to distinguish between the surface and interior birefringence of silica glass fibers as a function of drawing temperature and initial surface condition for two types of silica glass with different water contents. Fibers were drawn in a water‐free argon environment using graphite heating elements. It was found that fibers drawn at lower temperatures resulted in greater, interior birefringence, in agreement with previous reports. Additionally, it was found that in the case of low‐water silica glass, flame polishing via oxygen–hydrogen mixture and drawn into fibers at lower temperature resulted in significant surface compressive stress upon drawing. This compressive stress may be the result of surface stress relaxation in silica glass that occurs in the presence of water during fiber drawing. In silica glass that contains greater internal hydroxyl impurity concentrations, the interior birefringence as well as the surface stress relaxation was significantly reduced under the same fiber drawing conditions. Characterization of such stress responses provides insight into the effects of common processing techniques as well as impresses the significance of preform processing for consistent fiber production.

Spectral and infrared luminescent characteristics of 40PbO–35Bi2O3–25Ga2O3 glasses doped with Er3+

The heavy metal oxide glasses based on 40PbO–35Bi2O3–25Ga2O3 composition doped with different Er3+ ions content were synthesized in corundum crucible. The concentration dependences of band gap energy and Urbach energy in a series of glass samples were analyzed. The studied matrix showed wider IR transparency region comparing with other heavy metal oxide glasses containing PbO: up to 6.5 μm. The content of hydroxyl impurities NOH was evaluated based on infrared transmission spectra. The comparison of obtained NOH values with other oxide glasses indicate that studied composition has a moderate hydroxyl groups content. Luminescence properties of 4I13/2 → 4I15/2 transition were measured under 980 nm wavelength excitation. The correlation of radiative characteristics with NOH content was determined. The maximum relative luminescence intensity had the sample doped with 0.869 × 1020 ion/cm3 of Er3+. Comparative analysis of FWHM, peak value of emission cross-section, and radiative lifetime of 4I13/2 → 4I15/2 transition with other glass matrixes indicates the prospects of the investigated composition as advanced material for 1.5 μm optical amplifiers.

Effect of some hydroxyl additives on the growth and optical properties of KDP crystals

Potassium dihydrogen phosphate (KDP) single crystal was doped with disodium tetraborate decahydrate (or borax), L-alanine, and disodium ethylenediaminetetraacetate (or disodium EDTA) with 0.05 mol%, 9 mol%, and 2 mol% concentration in the aqueous solution, respectively. These crystals were fabricated by the temperature reduction method incorporating the Sankaranarayanan-Ramasamy technique and were grown onto seed crystals that were inclined at the type I phase-matching angle to the vertical. Each doped KDP single crystal rod was cut into three parts: the bottom, the middle, and the top, which were related to the fabrication temperature range of 50–40 °C, 40–30 °C, and 30–20 °C, respectively. The effect of the additives on the growth and optical properties of KDP crystals was evaluated through Ultraviolet–Visible spectroscopy, Raman spectroscopy, X-Ray Diffraction analysis, Energy-Dispersive X-ray spectroscopy, and Second Harmonic Generation measurement. The hydroxyl impurities have improved the optical properties of KDP crystals by contributing more hydrogen bonds to the KDP lattice. The doped KDP crystals increased SHG efficiency by 1.19 to 2.36 times compared with pure KDP crystals.

Internal OH\u2212 induced cascade quenching of upconversion luminescence in NaYF4:Yb/Er nanocrystals

Internal hydroxyl impurity is known as one of the main detrimental factors affecting the upconversion (UC) efficiency of upconversion luminescence (UCL) nanomaterials. Different from surface/ligand-related emission quenching which can be effectively diminished by, e.g., core/shell structure, internal hydroxyl is easy to be introduced in synthesis but difficult to be quantified and controlled. Therefore, it becomes an obstacle to fully understand the relevant UC mechanism and improve UC efficiency of nanomaterials. Here we report a progress in quantifying and large-range adjustment of the internal hydroxyl impurity in NaYF4 nanocrystals. By combining the spectroscopy study and model simulation, we have quantitatively unraveled the microscopic interactions underlying UCL quenching between internal hydroxyl and the sensitizers and activators, respectively. Furthermore, the internal hydroxyl-involved UC dynamical process is interpreted with a vivid concept of “Survivor effect,” i.e., the shorter the migration path of an excited state, the larger the possibility of its surviving from hydroxyl-induced quenching. Apart from the consistent experimental results, this concept can be further evidenced by Monte Carlo simulation, which monitors the variation of energy migration step distribution before and after the hydroxyl introduction. The new quantitative insights shall promote the construction of highly efficient UC materials.

First-principles calculations of strain engineering in NaYF4-based nanocrystals with hydroxyl impurities.

Lanthanide-based nanocrystals with heterogeneous core-shell structures possess elastic strain due to lattice mismatch and volumetric expansion or shrinkage. Strain relaxation is usually accompanied by lattice defects, especially those point defects and small defect clusters. However, the influence of strain on the formation of lattice defects remains unclear. Using OH- ions as a representative lattice impurity, first-principles calculations can be used to address the correlation between the thermodynamic stability of OH-based substitutional defects and elastic strain. Moreover, the concentration of OH- impurities in both strained and relaxed sodium yttrium fluoride lattices can be greatly reduced by increasing the concentration of fluoride-containing precursors. These findings suggest that minimal incorporation of OH- ions effectively suppresses multiphonon nonradiative relaxation and thus boost the efficiency of upconversion conversion.

Effect of indium incorporation, stimulated by UHV treatment, on the chemical, optical and electronic properties of ZnO thin film

Abstract We show the importance of powerful and complementary analysis techniques XPS (X-rays Photoelectron Spectroscopy), AES (Auger Electron Spectroscopy), and UPS (UV Photoelectron Spectroscopy) associated with PL (Photoluminescence) to investigate the chemical composition, optical emission, and electronic structure of undoped ZnO (UZO) and In-doped ZnO (IZO) thin films at the contaminated and clean states. The growth process of films on the Si substrate is achieved by ultrasonic spray pyrolysis. Both samples are submitted in the same conditions to cleaning treatment (argon ion etching followed by thermal annealing in Ultra High Vacuum UHV). The XPS and AES results display the great interest of physical UHV treatment to eliminate the contamination layer and stimulate the incorporation and oxidation of indium into the ZnO matrix. The PL measurements confirm that the UHV treatment allows the incorporation of indium into the ZnO matrix and eliminates wholly the visible emission due to hydroxyl impurities and defects such as oxygen interstitial and oxygen vacancies. The UPS technique is useful to show the electronic structure of the valence band and determine the work function, Fermi level, and the ionization potential of both samples.

Reaction ability of alternative mineral dispersed materials as a tool for developing efficient road composites

The avalanche-like growth of traffic intensity and freight traffic, the tightening of requirements for the quality of road clothes, the shortage of conditioned mineral raw materials in many regions of the Russian Federation prompt the construction materials science sector to search for new, promising methods for improving the quality of products. Road construction, one of the most material-intensive areas, is focused on maximizing the use of local, often non-conditioning materials, so composites made on their basis do not meet modern operational requirements. In this paper, a number of porous fine dispersed fillers have been investigated that could perform, on the one hand, the functions of a mineral powder, and on the other hand, serve as the carrier of a certain substance that regulates the properties of a road composite. The identification of the mechanism of interaction of mineral powders with bitumen was carried out by studying surface, physical-mechanical and chemical properties, as well as microstructural features and reactivity. It was found that the high porosity characteristic of fillers from perlite and zeolite is due to the highly developed pore architecture with the diameter of the entrance windows in a wide range. The study of the chemistry of the surface of a solid was carried out by evaluating the surface on which there are active centers due to the presence of hydroxyl groups and impurity centers. By the results of the experiment, it was found that an increase in the content of active sites on the surface of a mineral filler is directly proportional to its porosity. As a result of the conducted studies it was established that zeolites are the most promising raw material for organomineral composites. They have a developed specific surface, unique pore architecture, high structuring and adsorption capacity.

Spectral Luminescent Characteristics of Intrinsic and Uranium Color Centers in a LiF Crystal with Uranium, Magnesium, and Hydroxyl Impurities

Spectral Luminescent Characteristics of Intrinsic and Uranium Color Centers in a LiF Crystal with Uranium, Magnesium, and Hydroxyl Impurities

Modeling and optimization of porous silica ingot melting during quartz glass synthesis

Quartz glass is widely used in modern technologies due to its excellent thermophysical and optical properties. To reduce hydroxyl concentration, a critical impurity affecting optical performance and service life of the glass products, traditional synthesis process of the quartz glass is improved by melting the prepared porous silica ingot in a vacuumed furnace. Since the molten quartz encloses the porous silica ingot, and blocks escape of the gases, originated from hydroxyl or other impurities, the melting pattern should be optimally designed by controlling the operating conditions. In the paper, an integrated model has been developed to study the dynamic melting process of the porous silica ingot, considering heat transfer and large surface deformation. Influences of the heater temperature, the ingot size, the furnace cooling and the crucible design on the melting process are investigated carefully. Based on the analysis, an optimized crucible design with partial sidewall cooling of the furnace is proposed to obtain the preferred melting pattern for enhancing hydroxyl removal.

Synthesis and characterization of barium fluoride substituted zinc tellurite glasses

Glasses in the TeO2-ZnO-BaF2 system were prepared by standard melt quenching technique and were characterized for their thermal, optical and structural properties. Samples were found to show good thermal stability with values ranging above 100°C for all the compositions. Optical bandgap and refractive index values were calculated from linear optical measurements using UV-Vis spectroscopy. Infrared spectra showed the presence of hydroxyl groups in the glasses indicating that the effect of fluorine was negligible in removing the hydroxyl impurities for the experimental conditions and compositions used. Raman measurements showed the modification occurring in the glass network due to addition of barium fluoride in terms of increase in the formation of non-bridging oxygen atoms compared to strong Te-O-Te linkages in the glass matrix.

Magnetic and Optical Studies of 5%Mn and 5%Co Doped ZnO Synthesized by Sol Gel Wet Chemical Precipitation Route

Synthesis of Zn0.9Mn0.05Co0.05O was carried out using sol-gel wet chemical precipitation route. Synthesized product was characterized using by Transmission electron microscope (TEM) and FTIR spectroscopy. Analysis of TEM images reveals the particle size of Zn0.9Mn0.05Co0.05O in the range of 30-40 nm. FTIR spectroscopy results show hydroxyl and CO2 impurities in the sample. Magnetization with external field shows weak magnetic behavior of the sample at room temperature.

Modification of Structural and Vibrational Properties of ZnO Nanoparticles Prepared by Simple Chemical Precipitation Method

In this work, zinc oxide (ZnO) nanoparticles were synthesized by simple chemical precipitation method in the present of zinc nitrate as zinc precursor and sodium hydroxide as hydroxide precursor. The vitamin C was used as modifier media to modify the structural properties of ZnO nanoparticles. The microstructures of ZnO nanoparticles were characterized by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). Selected area electron diffraction (SAED) patterns showed that polycrystalline hexagonal phase of ZnO. The defects and impurity contents in nanoparticles were investigated by Fourier transform infrared (FT-IR) spectroscopy. The results show few carboxylate and hydroxyl impurities for larger particles when addition modifier increases. Surface areas of nanoparticles were measured by Brunauer Emmett Teller (BET) method. In addition, the results exhibited the dramatically change in structural properties of ZnO nanoparticles due to the effect of vitamin C.

The influence of sol–gel processing on the electrochromic properties of mesoporous WO3 films produced by ultrasonic spray deposition

High performance mesoporous tungsten oxide films were deposited by ultrasonic spray deposition using templated sol–gel chemistry. The dynamics of both sol preparation and hydrolysis were investigated by UV–vis spectroscopy. A stable sol was formed after 12h, while optimum electrochromic performance was obtained for 12h of hydrolysis. Electrochromic performance is strongly correlated to the annealing conditions, with optimized films displaying coloration efficiency >50cm2/C and switching times <10s. FTIR spectroscopy revealed that WO3 produced under optimized conditions were free of hydroxyl and carbonate impurities. Performance scaled with the specific surface area and nanoscale morphology. The WO3 films display good long term cycling durability up to 2500 cycles, which was attributed to the high degree of film crystallinity.

Hydroxyl Content of BaTiO3 Nanoparticles with Varied Size

Different types of tetragonal BaTiO3 particles were synthesized in a wet chemical process including an autoclave treatment. The synthesis and autoclaving medium was varied from isopropyl alcohol to water in different ratios, leading to a size variation of the particles from 38 to 145 nm. By applying combustion analysis of carbon and hydrogen (C/H analysis) released from the samples, it can be demonstrated that the amount of hydroxyl impurities incorporated into the crystal lattices of the particles increases with the water content of the synthesis medium. C/H analysis is a suitable tool for this characterization task as it allows discriminating different sources of these elements, i.e., different impurities. By comparing the self‐synthesized particles with commercial ones, it can be concluded that the particle size has the dominant influence on the tetragonality, if the amount of internal hydroxyl groups is relatively low. In contrast, if the amount of water originating from the internal OH groups is elevated (greater than ~0.4 wt%) an impairment of the tetragonality is caused.