Spectroscopic studies of TeO<Subscript>2</Subscript>–ZnO–Er<Subscript>2</Subscript>O<Subscript>3</Subscript> glass system

Series of glass based on the (80 − x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ≤ x ≤ 2.5 mol%) has successfully been made by melt quenching technique. The optical properties of glass have been investigated by means of IR and Raman spectroscopy. It is observed that as the Er₂O₃ content is being increased, the sharp IR absorption peaks are consistently shifted from 650 to 672 cm⁻¹ while the Raman shift intensity around 640–670 cm⁻¹ is decreases but increases around 720–740 cm⁻¹. It is found out that both phenomenons are related to the structural changes between the stretching vibration mode of TeO₄ tbp and TeO₃ tp, and bending vibration mode of Te–O bonds in the glass linkages.     

Fourier transform infrared spectroscopic estimation of crystallinity in SiO<Subscript>2</Subscript> based rocks

We present here optical properties and crystallinity index of quartz (SiO₂) in natural rocks samples from the Mikir and Khasi hills, Assam, India. Infrared spectroscopy has been used to study the structure of quartz in rock samples and estimate the mining quality of quartz mineral, which is substantiated by calculating the crystallinity index. Systematic investigations of structure have been carried out in between 10 μm (1000 cm⁻¹) and 20 μm (500 cm⁻¹) bands of silicates. Investigation is based on the assignment of infrared bands to certain structural groups of SiO₄ tetrahedra. The crystallinity of samples has been ascertained by comparing the ratio of intensity of the characteristic peak at 778 and 695 cm⁻¹ with the corresponding ratio for a standard sample. The crystallinity parameter is calculated by using a standard procedure which can be used to estimate the distribution of quartz in various rocks for mining purpose. The infrared spectroscopic investigation is found to be an ideal tool for structure elucidation and for estimating quartz crystallinity of the natural samples.     

Effect of neutron irradiation on the high-frequency IR spectra of quartz glass

We have studied the effect of neutron irradiation in a nuclear reactor on the high-frequency IR absorption spectra of quartz glasses. Three groups of bands were identified in the range 1400–2300 cm^?1 (at 1610, 1910, and 2270 cm^?1), and one group, in the range 2870–2970 cm^?1. The effects of neutron dose, ambient atmosphere, and sample geometry on these bands have been assessed. The results have been correlated with the irradiation-induced changes in the fundamental modes of the glass network and the luminescent and structural properties of the glasses. Mechanisms have been proposed for the radiation-induced changes in the spectral characteristics of some of the absorption bands. We assume activation of some combined frequencies at v > 1400 cm^?1 and local vibrations in the impurity region of the spectrum. High neutron doses produce marked changes in the IR spectrum, which seem to be associated with structural changes in the glass. The likely mechanism of such changes is discussed.     

Structural,optical and non-linear investigation of Eu<Superscript>3+</Superscript>: Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> sol-gel glass

Optical absorption and fluorescence spectra of Eu³⁺ ions in Al(NO₃)₃-SiO₂ sol-gel glass have been investigated using the Judd- Ofelt theory. JO intensity parameters (ω _λ ) and subsequent radiative properties for⁵ D ₀ ↔⁷ F _1,2,4,6 transitions are determined. The lifetime (τ_r) of⁵ D ₀ state is computed and along with JO parameters are compared with their corresponding values in other glasses prepared by conventional technique. A structural analysis, using IR and XRD spectra and non- linear parametrization of the silica gel glass is carried out. The study reveals the glass to be a very good third order non- linear amorphous optical material.     

Fabrication and characterization of Ge nanocrystalline growth by ion implantation in SiO<Subscript>2</Subscript> matrix

Ge nanocrystallites (Ge-nc) have been formed by ion implantation of Ge⁺⁷⁴ into SiO₂ matrix, thermally grown on p-type Si substrates. The Ge-nc are examined by Raman spectroscopy, photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR). The samples were prepared with various implantation doses [0.5; 0.8; 1; 2; 3; 4] × 10¹⁶ cm⁻² with 250 keV energy. After implantation, the samples were annealed at 1,000 °C in forming gas atmosphere for 1 h. Raman intensity variation with implantation doses is observed, particularly for the peak near 304 cm⁻¹. It was found that the sample implanted with a doses of 2 × 10¹⁶ cm⁻² shows maximum photoluminescence intensity at about 3.2 eV. FTIR analysis shows that the SiO₂ film moved off stoichiometry due to Ge⁺⁷⁴ ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeO_x at exactly the doses corresponding to the maximum blue-violet PL emission and the largest Raman emission at 304 cm⁻¹. This intensity reduction can be attributed to a larger portion of broken Ge–O bonds enabling a greater number of Ge atoms to participate in the cluster formation and at the same time increasing the oxygen vacancies. This idea would explain why the FTIR peak decreases at the same implantation doses where the PL intensity increases.     

Structure of WO<Subscript>3</Subscript>-TeO<Subscript>2</Subscript> glasses

WO₃-TeO₂ glasses have been studied by quantum-chemical simulation and Raman spectroscopy. The results have been used to develop a model for the network of tungstate-tellurite glasses. The model allows one to correlate the structure and optical properties (in particular, the position and intensity of Raman bands) of the glasses with their composition. The network of the glasses is shown to be made up, for the most part, of three types of structural groups: TeO₄ trigonal dipyramids, O=TeO₂ pyramids, and O=WO₅ octahedra. Any other structural units, in particular, WO₄ tetrahedra, are unnecessary. The model for the network of WO₃-TeO₂ glasses can be used to analyze the vibrational spectra of tungstate-tellurite glasses in a broad composition range. In particular, using this model we assigned the Raman spectra of the tungstate-tellurite glasses in the range 550–950 cm^?1.     

Microstructural evolution during direct laser sintering in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The microstructural evolution during direct laser sintering of LSD (Layerwise Slurry Deposition)—samples in the Al₂O₃–SiO₂ system has been investigated. Slurries with a water content of 34 wt.% and a SiO₂/Al₂O₃—ratio of about 3:1 have been used to manufacture layers which—after consecutive drying—have been sintered and laminated by laser treatment. Densified samples can be obtained with laser irradiances from 190 to 270 kW/cm² and scan velocities between 35 and 65 mm/s. Elemental mappings of the layers’ cross sections suggest an inhomogeneous phase distribution in the laser sintered LSD samples with a slight alumina concentration gradient. A lower degree of particle melting in the bottom region of the layers is plausible due to attenuation of the laser beam intensity. SEM and HRTEM micrographs show that after a few seconds of laser treatment relictic starting phase, crystalline alumina plus amorphous silica, occur together with needle like mullite, the latter formed within an amorphous aluminosilicate phase. The resulting phase assemblage reflects the non-equilibrium conditions which can be expected for short time laser treatments. Mullite nucleation within the bulk of the liquid phase rather than in the vicinity of the parent alumina phase suggests that dissolution of alumina is the rate controlling step. Subsequent thermal post treatment in air in a conventional sintering furnace causes an increase of density to about 96% and leads to additional phase reactions. Amorphous silica transforms into cristobalite and the amount of alumina is reduced by additional mullite formation. By both coalescence of individual crystals and grain growth the morphology of the newly formed mullite changes during post heat treatment.     

Effect of sintering temperature on the emission-spectrum-shape-evolution of Sr<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript> phosphor

Color rendering index and color temperature are the key factors for the LEDs application. The two points are closely related to the emission spectrum shape of phosphors. As the key factors for the LEDs application, both the above aspects are closely dependent on the emission spectrum shape of phosphors. In this study, the emission spectrum shape has been adjusted via a home designed route. A combination of structural, morphological, and optical characterization techniques has been used to study the shape evolution mechanism. The structural results show that the Sr₂SiO₄ phase has not been changed with the sintering temperature increasing, but the emission spectrum shape has changed dramatically, meanwhile, the colorimetric coordinate moves from blue-green to green region. Gaussian fitting method has been used to treat the emission spectrum, and the as-obtained results indicate the emission spectrum contains two single bands, which come from the 4f⁷(⁷S_7/2)–4f⁶(⁷F_J)5d¹ transition of Eu²⁺ on the different Sr sites in the Sr₂SiO₄ crystal. The intensity of the two single bands is driven by sintering temperature, because of the difference between the energy barrier of the Eu²⁺ occupying the different Sr sites in the matrix crystal. Moreover, the mechanism of the above phenomenon has also been studied by means of first principles method, and the obtained results agree well with the former deduction.     

Determination of the optical constants of HfO2–SiO2 composite thin films through reverse fitting of transmission spectra

Composite thin films of HfO₂:SiO₂ with wide range of relative composition from 100:0 (pure HfO₂) to 10:90 have been deposited on fused silica substrates by co-evaporation technique and the optical properties of the films have been studied by measuring the transmission spectra of the samples by spectrophotometer. Different important optical parameters viz., band gap, refractive index and absorption coefficients of the samples have been obtained by fitting the measured optical spectra with theoretically generated spectra and the variation of the optical constants as a function of SiO₂ content in the films have been obtained. Two different dispersion models viz., the single effective oscillator model and the Tauc–Lorentz model have been used to generate the theoretical spectra in the above fitting procedure. X-ray reflectivity (XRR) measurement technique has been used to find the densities of the films in order to explain the observed variation in optical properties of the films with increase in SiO₂ content.     

Radiation resistance diagnostics of wide-gap optical materials

Novel approach in the detection of radiation damage created by ion beams in optical materials was demonstrated. Protons of the energy of 100 keV and fluence of 10¹⁷ cm⁻² create sufficient amount of crystal lattice defects in the thin surface layer for testing of optical materials needed for future fusion reactors. These structural defects can be detected and analysed using the spectra of cathodoluminescence excited in the irradiated layer by an electron beam with adjustable energy. The method was verified by the enhanced intensity of F-type luminescence that reflects the creation of radiation-induced oxygen vacancies in MgO and Al₂O₃ crystals. Low radiation resistance of nominally pure (Lu_1-xGd_x)₂SiO₅ crystals was demonstrated by almost total suppression of intrinsic luminescence after the same irradiation.     

Physicochemical properties of La<Subscript>3</Subscript>Ga<Subscript>5.5</Subscript>Ta<Subscript>0.5</Subscript>O<Subscript>14</Subscript>

We report the optical and dielectric properties and microhardness of La₃Ga_5.5Ta_0.5O₁₄ lanthanum gallium tantalate (langatate) crystals. Analysis of the optical transmission spectra of the crystals in relation to their refined compositions indicates that the bands at 34000–35000 and 27000–28000 cm⁻¹ are due to lanthanum and oxygen vacancies, respectively, and that the band at 20000–21000 cm⁻¹ is responsible for the yellow (orange) coloration of the crystals. Their resistivity and microhardness decrease with increasing oxygen vacancy concentration.     

Radiation-induced optical emission quenching in light-probed silica core fibers

The radiation-induced visible emission (400–750 nm) intensity in an optical fiber with a KU-1 silica glass core (OH group content, 1000 ppm) was measured in the fiber irradiated in a pulse mode [BARS-6 reactor; pulse duration, 80 μs; dose per pulse, <5.5×10¹² cm^?2 (9 Gy); dose rate, <7×10¹⁶ cm^?2 s^?1 (1.1×10⁵ Gy/s)]. The fiber probed by laser pulses (at 532 and 632 nm) with increasing intensity showed a decrease in the radiation-induced emission intensity in the regions of wavelength both greater and lower than and equal to the probing light wavelength.     

Manifestation of Nd ions on the structure,Raman and IR spectra of (TeO<Subscript>2</Subscript>-MoO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>) glasses

The structure of [80TeO₂ + (20–x)MoO + xNd₂O₃] glasses, with x = 0, 4, 6, 10 and 12 mol%, is studied in this work. Raman scattering in the spectral range (−2000 to 3500 cm⁻¹) and IR absorption spectra have been measured for crystalline TeO₂ and glasses, and their assignments were discussed and compared. Many vibrational modes were found active in both Raman and IR and their assignments for crystalline TeO₂ and for the glasses were discussed in relation to the tetragonal structure of crystalline α -TeO₂. Nd₂O₃ was found to completely eliminate diffuse scattering and enhance the Raman scattering intensity. Anti-stokes Raman bands in the range −1460 cm^{− 1} to −1975 cm^{− 1} were observed for both (30Li₂O + 70B₂O₃+ xNd₂O₃) glasses and [80TeO₂ + (20−x)MoO + xNd₂O₃] glasses and were attributed to some emission processes due to the doping of the glasses with Nd₂O₃.     

The ferroelectric properties and residual stress analysis of Bi<Subscript>3.15</Subscript>Nd<Subscript>0.85</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films with a LaNiO<Subscript>3</Subscript> buffer layer

Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin film with a thin LaNiO₃ film as buffer layer was fabricated by sol–gel method on Pt/TiO₂/SiO₂/Si substrate. The BNT thin films have a perovskite phase with a dense microstructure. The P _r and V _c value are 25.5 μc/cm² and 3.7 V, respectively under the applied voltage of 15 V. After the switching of 2 × 10⁹ cycles, the P _r value decreases to 86% of its pre-fatigue value. The leakage current density of the BNT thin films with LaNiO₃ buffer layer were generally in the order of 10⁻⁸ to 10⁻⁶ A/cm². The fatigue and leakage current properties were improved dramatically compared with the BNT film without a LaNiO₃ buffer layer that we prepared before. The measured residual stress was tensile stress and its value was 176 MPa.     

Structural and surface morphological properties of chemically deposited Mo<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>S<Subscript>2</Subscript> thin film

Preparation of layered type semiconductor Mo_0.5W_0.5S₂ ⁻ thin films has been successfully done by using chemical bath deposition method. Objective of the studies are related to structural, optical, morphological and electrical properties of the thin films. The preparation method is based on the reaction between tartarate complex of Mo and W with thiourea in an aqueous alkaline medium at 363 K. X-Ray diffraction reveals a polycrystalline film composed of both MoS₂ and WS₂ phases. The optical study shows that the band gap of the film is 1.6 eV. Electrical conductivity is high which is in the order of 10⁻³–10⁻² (Ώ cm)⁻¹.     

Evolution of the structure and magneto-optical properties of ion beam synthesized iron nanoclusters

Changes in the structural, magnetic, and optical properties are observed during the synthesis of metallic nanoclusters fabricated on the surface of a thin silica layer by ion beam implantation of iron atoms. Iron atoms were implanted to the fluence of 10¹⁶ cm⁻². The ion implantation depth in 400-nm thick SiO₂ film on a Si (100) substrate was 25 nm. The implanted samples were subsequently annealed for periods of seconds to hours at 1000 °C with Electron Beam Annealing. Ellipsometry and Rutherford Backscattering Spectrometry spectra were fitted with appropriate models to retrieve the optical characteristics, composition, and structure of the samples. Magneto Optical Kerr Effect measurements and SQUID magnetometry were performed to investigate the effect of the structural changes identified by TEM measurements on the superparamagnetic and magneto-optical properties of the samples during the annealing process. The changes in the Fe crystalline(core)/amorphous oxide(shell) structure and the position of the nanoclusters relative to the surface observed for small annealing durations are shown to enhance the Kerr effect resulting into high coercive field and high amplitude in the Kerr rotation and ellipticity.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Effect of doping with transition and rare-earth metals on the electrical and optical properties of AgGaGe<Subscript>3</Subscript>Se<Subscript>8</Subscript> single crystals

We have studied the electrical, optical, and thermoelectric properties of AgGaGe₃Se₈ single crystals grown by the Bridgman-Stockbarger method and doped with transition and rare-earth metals during growth. AgGaGe₃Se₈ is an anisotropic p-type semiconductor with a band gap of ～2.25 eV (T ～ 290 K), which decreases slightly, to ～2.20 eV, on doping with Nd, Gd, and Er (N ～ 5 × 10¹⁸ cm^?3). The high concentration of stoichiometric silver vacancies (N ～ 1.8 × 10²⁰ cm^?3) and random distribution of the Ga and Ge atoms over the cation sites give rise to static disorder, so that the structure of AgGaGe₃Se₈ approaches that of disordered systems. This leads to the formation of electronic states in the band gap, intrinsic edge broadening, and, as a consequence, a drop in transmission. Depending on the concentration and nature of the dopant, doping of AgGaGe₃Se₈ may lead to structural ordering and bleaching or may increase the destructive factor at high doping levels (N > 10¹⁸ cm^?3). ⁶⁰Co gamma irradiation to a dose of 1.2–1.3 kGy reduces the absorption coefficient of AgGaGe₃Se₈ crystals doped with high concentrations of Mn and Cu (N > 5 × 10¹⁸ cm^?3). A model is proposed which explains the observed effects.     

Effects of oxygen and carbon impurities on the optical transmission of As<Subscript>2</Subscript>Se<Subscript>3</Subscript> glass

The IR spectra of As₂Se₃ glass samples containing known amounts of oxygen (4 × 10^-3 to 7.7 × 10^-2 wt %) or carbon (5.8 × 10^-3 wt %) are measured, and the parameters of impurity-related absorption bands and extinction coefficients are determined. The effects of oxygen, carbon, sulfur, and hydrogen on the transmission of As₂Se₃ glass are analyzed. At an oxygen content on the order of 10^-5 wt %, this impurity causes optical losses in the range 900–1100 cm^-1 comparable to the intrinsic losses. The permissible carbon content of As₂Se₃ glass is 10^-6 to 10^-5 wt %. Carbon inclusions 0.07 µm in diameter cause optical losses comparable to the intrinsic losses in the spectral window of As₂Se₃ glass when present in a concentration of 10⁴ cm^-3.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 369–376.Original Russian Text Copyright © 2005 by Shiryaev, Smetanin, Ovchinnikov, Churbanov, Kryukova, Plotnichenko.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Determination of CaCO<Subscript>3</Subscript> and SiO<Subscript>2</Subscript> content in the binders of historic lime mortars

The binders of historic mortars composed of small grain sized silica (SiO₂) and carbonated lime (CaCO₃) are considered as the main part that give hydraulic character and high strength to the mortar. In this study, FTIR, SEM–EDS, LIBS and XRD spectroscopy were used to find out the weight ratios of CaCO₃ to SiO₂ in the binders of historic lime mortars. For this purpose, a series of pure calcium carbonate and silica mixture were prepared in ten combinations in varying ratios from 0.5 to 5. Calibration curve was prepared for each analysis by plotting the peak area or intensity ratios of CaCO₃ to SiO₂ versus the weight ratios of CaCO₃ to SiO₂. A good linear correlation coefficient was obtained for each analysis respectively. The analyses were then tested on the binder of the Roman mortar samples. The results indicated that FTIR, SEM–EDS and LIBS spectroscopy are convenient tools to determine the weight ratios of CaCO₃ to SiO₂ in the binders of mortars. But XRD spectroscopy is not convenient for quantitative analysis of binders due to the presence of varied amounts of amorphous or poor crystalline silica in their compositions.