Infrared absorption in spinel ferrites

Their spectra of a number of ferrites, MFe₂O₄, M(Mn, Fe, Co, Ni, Cu and Zn) have been studied at room temperature in the range 200–1000 cm⁻¹. In all the cases the spectrum consists of four bands, two of which have strong absorption while the other two have weak absorption and often appear as shoulders on the main band. However up to 20% of the inverse ferrite, the shoulder in the low energy side appears as a band. In this paper we have analysed the origin of the above bands.     

Optical properties of CdS sintered film

Chemical method has been used to prepare cadmium sulphide by using cadmium, hydrochloric acid and H₂S. The reflection spectra of covered and uncovered sintered films of CdS have been recorded by ‘Hitachi spectrophotometer’ over the wavelength range 300–700 nm. The energy band gaps of these films have been calculated from reflection spectra. It is found that the energy band gap of both films is same as 2.41 eV. It is indicated that energy band gap of these films does not change. This value of band gap is in good agreement with the value reported by other workers. The measurement of photocurrent has also been carried out using Keithley High Resistance meter/ Electrometer. This film shows the high photosensitivity and high photocurrent decay. Thus so obtained films are suitable for fabrication of photo detectors and solar cells.     

Some physical properties of an Al2O3-SiC-TiC composite

Ceramic samples obtained by hot pressing from a mixture of Al₂O₃ with admixtures of 23 vol.% TiC powder and 30.9 vol.% SiC whisker crystals are investigated experimentally. The resistivity of the material is measured at temperatures of 4.2–300 K, the infrared reflection spectra are recorded in the region 400–4200 cm^–1, and the temperature dependence of the Young’s modulus is investigated at temperatures up to 1300 K. As a result it is it is shown that the conductivity and optical reflection of the high-strength composite have a semimetallic character, which is due to the titanium carbide particles contained in it. Pis’ma Zh. Tekh. Fiz. 23, 52–58 (December 12, 1997)     

Effect of deposition conditions on the InP thin films prepared by spray pyrolysis method

InP thin films were prepared by spray pyrolysis technique using aqueous solutions of InCl₃ and Na₂HPO₄, which were atomized with compressed air as carrier gas. The InP thin films were obtained on glass substrates. Thin layers of InP have been grown at various substrate temperatures in the range of 450–525°C. The structural properties have been determined by using X-ray diffraction (XRD). The changes observed in the structural phases during the film formation in dependence of growth temperatures are reported and discussed. Optical properties, such as transmission and the band gap have been analyzed. An analysis of the deduced spectral absorption of the deposited films revealed an optical direct band gap energy of 1.34–1.52 eV for InP thin films. The InP films produced at a substrate temperature 500°C showed a low electrical resistivity of 8.12 × 10³ Ω cm, a carrier concentration of 11.2 × 10²¹ cm⁻³, and a carrier mobility of 51.55 cm²/Vs at room temperature.     

Magnetic nanocomposites of mixed oxides of iron and barium synthesized under different oxidative environments

Synthesis of nanocomposites of mixed oxides of iron and barium in a copolymer matrix of aniline and formaldehyde using a chemical route at room temperature is reported. X-ray diffraction, infrared, ⁵⁷Fe Mossbauer studies, and scanning electron microscopy on as-synthesized samples, as well as samples obtained on heating at different temperatures, are described. X-ray diffraction, ⁵⁷Fe Mossbauer, and scanning electron microscopy show the formation of nanoparticles of barium ferrites in the polymer matrix. These studies further show the formation of solid solution of iron and barium oxide on heating the samples at temperatures from 400 to 700°C. From the Mossbauer and x-ray diffraction studies, it has been found that γ-Fe₂O₃, which normally transforms into α-Fe₂O₃ on heating at 500°C, persists up to 700°C in the present samples containing barium ions. Infrared studies indicate that the polymeric backbone is strongly influenced by different reaction conditions and lead to variable magnetic character in the heated samples. The text was submitted by the authors in English.     

Optical properties of samarium doped zinc-tellurite glasses

Glasses with the composition, (Sm₂ O ₃) _x (ZnO)_(40-x)(TeO ₂)₍₆₀₎, were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been explained.     

Optical properties of TlInS2 layered single crystals near the absorption edge

The sample thickness effect on the optical properties of TlInS₂ layered crystals has been investigated at room temperature. The absorption coefficient of the samples calculated from the experimental transmittance and reflectance in the photon energy range of 1.10–3.10 eV has two absorption regions. The first is a long-wavelength region of 1.16–1.28 eV. The second region lies above 2.21 eV with a thickness-dependent indirect band gap. The energy gap decreases from 2.333 to 2.255 eV as the sample thickness increases from 27 to 66 μm. The differential spectra of absorption coefficient demonstrates the existence of a thickness-dependent impurity level being lowered from 2.360 to 2.307 eV as sample thickness increases from 27 to 66 μm.     

Density of states effective mass of SnBi<Subscript>4</Subscript>Se<Subscript>7</Subscript> deduced from the temperature dependence of electrical conductivity in the activation regime

Current–voltage (I–V) measurements on polycrystalline samples of Bi₂Se₃ and stoichiometric ternary compound in the quasi-binary system of SnSe–Bi₂Se₃ at different temperatures in the vicinity of room temperature have been performed. Also, temperature dependence of electrical conductivity has been measured. From the analysis of the temperature dependence of electron concentration in the activation regime above room temperature, the density of states effective mass, m*, has been determined. Some intrinsic and contact properties such as barrier heights, ideality factors, and carriers concentrations have been investigated using I–V characteristics. It has been found that all samples exhibit ohmic and space charge limited conduction at low and high fields, respectively.     

Visible photoluminescence of hydrothermal synthesized Sn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> nanostructures

Sn_1−x Ni _x O₂ nanostructures such as nanocubes, nanospheres and hollow spheres were synthesized by a simple hydrothermal method. Room temperature photoluminescence spectra of the as-synthesized samples display a strong yellow emission at about 600 nm and a weak blue emission at about 430 nm. The as-prepared and annealed Sn_1−x Ni _x O₂ (x = 0, 0.01, 0.02, 0.04) were characterized by X-ray diffraction, field emission scanning electron microscopy, Raman spectrum, UV–Vis absorption spectra, and room temperature photoluminescence spectra. By investigating the relationship between the Raman band centered at 560 cm⁻¹ and the photoluminescence of the samples, we suggest that the broad yellow emission and weak blue emission primarily originate from singly ionized oxygen vacancies and tin interstitials, respectively.     

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl₂·2H₂O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS₂ compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 10³ Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 10³ Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 10³ to 0.55 × 10³ Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.     

Structural,optical and magnetic characterization of Cu-doped ZnO nanoparticles synthesized using solid state reaction method

Polycrystalline undoped and Cu-doped Zinc oxide (Zn_0.98Cu_0.02O) nanocrystals were successfully synthesized by solid-state reaction method. The micro structural, optical and magnetic properties have been characterized using powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive analysis using X-rays (EDAX), UV–Visible spectroscopy, Photoluminescence, Vibrating sample magnetometer and Electron paramagnetic resonance spectroscopy. XRD pattern reveals that the samples possess hexagonal wurtzite structure of ZnO without any secondary phase after copper doping. Optical absorption analysis of the samples showed a red shift in absorption band edge with copper doping in ZnO. Photoluminescence spectra of the samples shows prominent peaks corresponding to near band edge UV emission and defect related green emission in the visible region at room temperature and their possible mechanism have also been discussed. Magnetic measurements using VSM showed that the nanocrystalline copper doped ZnO exhibits ferromagnetic behaviour at 300 K. EPR analysis also confirms the substitution of Zn site by Cu²⁺.     

Synthesis of CaTiO<Subscript>3</Subscript>:Pr,Al phosphors by a peroxide-based route and their photoluminescence properties

A enhanced photoluminescence red phosphor of CaTiO₃:Pr,Al has been synthesized by a peroxide-based route (PBR) and high temperature sintering method. The synthesizing conditions have been optimized in this work. The effect of sintering temperature and boron on the preparation, structure, and photoluminescence were studied by X-ray powder diffraction (XRD), emission, and excitation spectra at room temperature. The red emission is attributed to ¹ D ₂ → ³ H ₄ transition of Pr³⁺, and the excited energy comes from the UV absorption of host and transfers to 4f–5d band of Pr³⁺. Also, the studies include analysis of charge compensation and Pr³⁺ concentration effects. Compared with conventional solid-state reaction methods, the PBR significantly lowered temperatures of synthesis, shortened reaction time, and enhanced the photoluminescence intensity.     

Optical and photoelectric properties of α-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript> and α-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Pb〉 films

A process is described for the growth of thin crystalline α-Dy₂S₃ films by thermal evaporation from separate dysprosium and sulfur sources. The films were doped with Pb, and their reflection and transmission spectra were measured at room temperature and photon energies in the range (0.3−5.2) × 10⁻¹⁹ J. The α-Dy₂S₃ films were shown to have an exponential absorption edge. The photoconductivity of the doped films was measured at photon energies in the range (0.3−5.2) × 10⁻¹⁹ J and temperatures from 115 to 400 K.     

Cathodoluminescence and scintillation characteristics of YAG:Ce crystals grown by horizontal directional crystallization in a protective atmosphere

YAG:Ce crystals have been grown by a new gas-phase horizontal directional crystallization (HDC) technique in a protective atmosphere and their cathodoluminescence (CL) spectra and scintillation characteristics have been studied. Using this HDC technology, it is possible to obtain large (110 × 150 × 35 mm) crystals with a high specific light yield (15 000–18 000 Ph/MeV) and good amplitude resolution (8–10%) for the excitation with 5.15-MeV α particles from a ²³⁹Pu source. In addition to an intense band at 550 nm due to Ce³⁺ ions, the CL spectra of crystals display an intrinsic emission band of YAG in the UV spectral range, which is due to the presence of Y_Al antisite defects.     

Electrical conduction and relaxation mechanism in Li<Subscript>2</Subscript>AlZr[PO<Subscript>4</Subscript>]<Subscript>3</Subscript>

Li-ion electrolyte NASICON type Li₂AlZr[PO₄]₃ has been prepared by Solid State Reaction method. Formation of the sample has been confirmed by XRD and TGA–DTA analysis. Electrical conductivity studies have been performed in the frequency range 42 Hz–5 MHz within the temperature range 523–623 K using aluminium as blocking electrodes. The conductivity has been found to be 1 × 10⁻⁵ S cm⁻¹ at 623 K. Dielectric spectra show the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the sample. Spectroscopic plots of complex modulus suggest the Non-Debye behaviour of the electrical relaxation within the temperature range studied.     

Infrared whispering-gallery-mode lasers (λ= 2.4 μm) with convex disk cavity operating at room temperature

A whispering gallery mode (WGM) semiconductor laser with a convex disk cavity operating at room temperature in the middle-IR range (λ = 2.4 μm) has been created for the first time. The convex cavity was formed by etching in a specially selected CrO₃-HF-H₂O mixture. The room-temperature emission spectra have been measured. The laser generates WGMs at room temperature in a pulsed regime.     

Microstructure, optical and dielectric properties of compositional graded (Ba,Sr)TiO3 thin films derived by RF magnetron sputtering

Thin films of compositional graded Ba_1−x Sr _x TiO₃ (BST) (x decreasing from 0.3 to 0) were prepared on fused quartz and Pt/Ti/SiO₂/Si substrates by RF magnetron sputtering. The microstructure of the graded BST thin films was characterized by X-ray diffraction (XRD). It indicates that the films were crystallized with peroveskite structure and (100) + (111) preferred orientation. The refractive index and the band gap were determined at room temperature in the wavelength 200–1100 nm from spectrophotometric measurements of the transmittance. The average value of the refractive index is found to be 2.17 for the graded BST films in the wavelength 400–1000 nm. The optical band gap of the graded BST film was 3.77 eV. The dielectric measurement showed that the dielectric constant and loss factor of the graded BST film was 318.04 and 0.028 at 100 KHz and room temperature.     

Photoluminescent properties of ZnS:Mn nanoparticles with in-built surfactant

Mn-doped ZnS nanoparticles, having average diameter 3–5 nm, have been synthesized using chemical precipitation technique without using any external capping agent. Zinc blende crystal structure has been confirmed using the X-ray diffraction studies. The effect of various concentrations of Mn doping on the photoluminescent properties of ZnS nanoparticles has been studied. The time-resolved photoluminescence spectra of the ZnS:Mn quantum dots have been recorded and various parameters like lifetimes, trap depths, and decay constant have been calculated from the decay curves at room temperature. The band gap was calculated using UV–Visible absorption spectra.     

Sputtered rutile stoichiometric TiO2 nanocrystalline films

Titanium dioxide (TiO₂) films were prepared at room temperature on silicon and glass substrates using DC reactive magnetron sputtering at the rate of 0.1 nms⁻¹ from a pure metal Ti target. X-ray diffraction (XRD) studies on freshly prepared samples showed a purely rutile phase. It is found from AFM that annealing of fresh TiO₂ films at 550°C for 30 min produced an increase in grain size by a factor of at least 1.5. X-ray photoelectron spectroscopies (XPS) gives correct ratio for purely TiO₂ stoichiometry. Optical band gap was estimated to be 3.2 eV from UV–vis transmission spectra.     

Amorphous Li–B–W–O solid-state electrolyte thin film for a solid-state ionic power sources

Li–B–W–O thin film serving as a solid-state electrolyte layer for a solid-state thin film battery has been deposited on a stainless steel (SUS)/Si substrate by thermal evaporation deposition at room temperature. By energy dispersive X-ray spectroscopy and inductively coupled plasma-atomic emission spectrometer measurements, the as-grown thin film showed a stoichiometry of Li_2.99BW_1.8O₉. The as-grown Li–B–W–O solid-state electrolyte thin film possessed an amorphous structure as confirmed by X-ray diffraction. Field emission scanning electron microscopy measurements of the film cross section showed a dense structure that did not have any large defects such as cracks or voids. For a cell structure of SUS/Li–B–W–O/SUS/Si, an impedance measurement conducted at room temperature revealed an ionic conductivity of 2.15 × 10⁻⁷ S cm⁻¹ with activation energy of 0.52 eV, which suggests that Li–B–W–O thin film can possibly be used as an electrolyte in solid-state thin film batteries.