Volume 38 (2020): Issue 3 (September 2020)

TiO₂ thin films have been deposited on glass substrates with and without ZnO underlayer by sol-gel dip coating process. XRD patterns show the formation of anatase phase with the diffraction lines (1 0 1) and (2 0 0) in TiO₂/glass sample. In TiO₂/(ZnO/glass) sample, TiO₂ is composed of anatase phase with the diffraction line (2 0 0) but the diffraction peaks of ZnO wurtzite are also well-defined. The determination of the refractive index and the thickness of the waveguiding layers has been performed by m-lines spectroscopy. The thickness of TiO₂ thin films deduced by Rutheford Backscattering Geometry (RBS) agrees well with that obtained by m-lines spectroscopy. TiO₂/glass sample exhibits one guided TE₀ and TM₀ polarized modes. In TiO₂/(ZnO/glass) sample, only, TE₀ single mode has been excited due to cutoff condition.

The geometries, electrostatic potential, Mulliken charge analysis, Natural Bond Orbital analysis and polarizabilities of propyl-para-hydroxybenzoate were calculated using B3LYP functional with 6-311++G(d,p) basis set. The calculated geometries are well matched with the experimental values. The Mullliken atomic charge analysis shows that the eventual charges are contained in the molecule. The NBO analysis explains the intramolecular charge transfer in the PHB molecule. The bonding features of the molecule were analyzed with the aid of Hirshfeld surface analysis. The frontier molecular orbital analysis showed the charge transfer obtained within the molecule. The calculated hyperpolarizability of the PHB molecule was 6.977E ⁻³⁰ esu and it was 8.9 times that of standard urea molecule.

In this work, the Ni/Co/Si system was annealed at temperatures ranging from 300 °C to 800 °C. The samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and sheet resistance measurement. The XRD and Raman spectroscopy results showed that the formation of nickel and cobalt silicides (CoSi, Co₂Si, Ni₂Si, NiSi, NiSi₂, CoSi₂) is an annealing temperature dependent diffusion process. The diffusion phenomenon was evidenced by RBS. The low values of the sheet resistance which were correlated with the films surface roughness were attributed to the formation of both CoSi and NiSi phases.

Ceramic lead niobates and their solid solutions (1 – x)Pb(Sc_0:5Nb_0:5)O₃ – xPb(Yb_0:5Nb_0:5)O₃ were synthesized by solid state reactions from oxides. The structure of investigated samples was characterized by X-ray diffraction (XRD). Dielectric studies of the ceramics were performed by means of broadband dielectric spectroscopy at the temperature ranging from 600 K to 140 K. For all ceramic samples a diffuse phase transition as well as relaxor ferroelectric behavior were observed.

SiO₂ particles and red-emitting CaMgSi₂O₆:Eu²⁺,Mn²⁺ phosphor have been added into a yellow phosphor compound YAG:Ce³⁺ to enhance the optical efficiency of white light LEDs whose average correlated color temperature (CCT) is in the range of 5600 K ÷ 8500 K. It was observed that altering CaMgSi₂O₆:Eu²⁺,Mn²⁺ concentration from 2 % to 30 % while maintaining 5 % of the SiO₂ strongly influenced the color rendering index (CRI), color quality scale (CQS), and lumen efficiency of the compound. Besides, through the application of Monte Carlo simulation and Mie-scattering theory, it was possible to improve the optical properties by CaMgSi₂O₆:Eu²⁺,Mn²⁺ and SiO₂ addition. The results provided a practical approach to achieve higher luminous efficiency and better color uniformity in remote-phosphor white LEDs (RP-WLEDs).

In this research, polyurethane (PU)/tetraethyl orthosilicate (TEOS) composite was prepared via one-step polymerization method using different concentrations of TEOS in PU. The structural, optical and physical properties of PU composite were characterized by SEM imaging, FT-IR spectroscopy, water uptake, Raman spectroscopy and optical microscopy imaging of synthesized samples. The SEM results showed that by adding TEOS to the PU, the cell and window size of synthesized samples decreased. This result was also observed in the optical micrographs. The bonding characteristics of PU/TEOS composites were analyzed using Raman and FT-IR spectra. According to the FT-IR spectra, the degree of phase separation (DPS) and hydrogen bonding index, R, in 800 μl TEOS/PU had the highest R and DPS factors. By adding different concentrations of TEOS to PU, the apparent density decreased but the real density increased. The total, open and closed porosity of the synthesized samples were calculated. At low loading of TEOS in PU, the open porosity of the samples increased. The PU/TEOS composites may be promising candidates for absorbing sound.

TiO₂ thin films with different surface structure have been prepared from alkoxide solutions by the sol-gel method using different cationic precursors and heat treatment techniques. The effect of using titanium isopropoxide as well as titanium butoxide as a titanium source on the surface structure and photocatalytic activity of the resultant thin films was studied. Significant differences in the rate of hydrolysis and condensation reactions during the sol-gel synthesis were observed for these titanium precursors. This had a direct influence on the morphology of the as-prepared TiO₂ films. Higher quality oxide coatings were obtained from titanium isopropoxide. They were characterized by a smaller grain size, improved surface roughness and uniform coverage of the glass substrate. A beneficial effect of calcination process after each sol application cycle in contrast to single step calcination after all dip-coating cycles was observed. Photocatalytic degradation tests showed that methyl orange was decolorized in the presence of all prepared TiO₂ films by exposing their aqueous solutions to UV light (λ = 254 nm). The highest photocatalytic activity had the TiO₂ layer produced using titanium isopropoxide.

This article discusses the growth and characterization of (((4-sulfonatophenyl) ammonio)oxy) zirconium (SAOZ) single crystals. Sulphanilic acid incorporated zirconium oxychloride semi-organic single crystals have been synthesized by slow evaporation technique. From the X-ray studies, lattice parameters a = 7.31 Å, b = 7.51 Å, c = 13.92 Å, volume = 765 ų have been found and so the crystal has been identified as orthorhombic with non-centrosymmetric space group P2₁2₁2₁. The powder XRD examination demonstrated the quality and high crystalline nature of the grown crystal. The presence of functional groups was confirmed by FT-IR technique. The chemical structure of the compound was established by ¹H and ¹³C NMR spectra. The optical transmittance window and the low cutoff wavelength of SAOZ have been identified by UV-Vis-NIR studies. Photoluminescence studies showed a wide blue light emission. TG and DTA examinations were carried out to characterize the thermal behavior of the grown crystal. The mechanical strength of the grown crystal was analyzed by the Vickers microhardness test. The elemental analysis was done by EDAX. The dielectric response of the crystals was analyzed in the frequency range of 50 Hz to 5 MHz at various temperatures and the outcomes were discussed. The SHG efficiency was estimated in correlation with KDP by employing powder Kurtz method.

The purpose of the present investigation was to prepare pH-sensitive hydrogels from photo-crosslinked poly(ethylene glycol) diacrylate (PEG-DA). Rutile titanium dioxide (TiO₂) was employed to modify the PEG-DA hydrogels. The rutile titanium dioxide (TiO₂) nanoparticles were prepared by direct oxidation of titanium in the presence of polyethylene glycol (PEG) at high temperature. The nanoparticles were characterized by FT-IR, XRD and SEM. The influence of experimental conditions, such as pH, type and amount of photoinitiators on the release profiles of donepezil hydrochloride (active pharmaceutical ingredient for Alzheimer disease) from modified PEG-DA hydrogels, was investigated. The drug release processes were analyzed kinetically using zero-order, first-order, Hixson-Crowell and Peppas models.

In this research, a series of Ru(II) complexes, ([Ru(1-7)(ina)(NCS)₂] (1-7=5-[6-(5-mercapto-1,3,4-oxadiazol-2-yl)pyridin- 2-yl]-1,3,4-oxadiazole-2-thiol’s, ina=isonicotinic acid) were synthesized and characterized using different spectroscopic and analytic techniques, such as NMR, UV, IR, CV and CHN. Also, the new complexes were used in dye-sensitized solar cells (DSSC) as sensitizers. Current-voltage characteristics showed that the modifications of ligands clearly affected DSSC yield. Additionally, DFT calculations were performed and showed locations of frontier molecular orbitals of the complexes. While the locations of HOMO and HOMO – 1 orbitals are on Ru(II) metal center and SCN⁻ ligands, the location of LUMO and LUMO + 1 orbitals are on the 1-7 ligands.

The development of transparent conducting oxide materials has gained an increased interest in the scientific community for developing efficient low cost optoelectronic devices. The effect of Cd precursor on structural and optical properties of sol-gel synthesized Zn_0:9Cd_0:1O nanostructured films has been studied by using XRD, AFM, optical absorption and emission spectroscopic techniques. X-ray diffraction confirms the hexagonal wurtzite crystal structure of the deposited films and the relative intensity of diffraction peaks has been observed with different cadmium salts. The granular surface morphology of the synthesized films has been observed from AFM measurements. The optical transmission, band gap and luminescence intensity was found to change for different cadmium salts. These results are very important for developing new materials for optoelectronic applications.

Lithium tantalate solid solution, Li_3+5xTa_1−xO₄ was prepared by conventional solid-state reaction at 925 °C for 48 h. The XRD analysis confirmed that these materials crystallized in a monoclinic symmetry, space group C2/C and Z = 8, which was similar to the reported International Crystal Database (ICDD), No. 98-006-7675. The host structure, β-Li₃TaO₄ had a rock-salt structure with a cationic order of Li⁺:Ta⁵⁺ = 3:1 over the octahedral sites. A rather narrow subsolidus solution range, i.e. Li_3+5xTa_1−xO₄ (0 ⩽ x ⩽ 0.059) was determined and the formation mechanism was proposed as a replacement of Ta⁵⁺ by excessive Li⁺, i.e. Ta⁵⁺ ↔ 5Li⁺. Both Scherrer and Williamson-Hall (W-H) methods indicated the average crystallite sizes in the range of 31 nm to 51 nm. Two secondary phases, Li₄TaO_4:5 and LiTaO₃ were observed at x = 0.070 and x = −0:013, respectively. These materials were moderate lithium ionic conductors with the highest conductivity of ~2.5 × 10⁻³ Ω ⁻¹ ˙ cm−¹ at x = 0, at 0 °C and 850 °C; the activation energies were found in the range of 0.63 eV to 0.68 eV.

In this study, CuO/n-Si/Al heterojunction contacts were fabricated by thermal evaporation technique. Electrical characteristics of the samples were investigated with the current-voltage (I-V), capacitance-voltage/frequency (C-V/f), and conductancevoltage (G/V) measurements at room temperature. Also, Cu/n-Si/Al Schottky contact was produced as a reference sample to investigate the electrical properties of the samples. The values of ideality factor (n), barrier height ( Φ_b) and series resistance (R_s) of the samples were calculated from the forward bias current-voltage (I-V) and reverse bias capacitance-voltage (C-V) characteristics. Also, for checking the consistency of the results, Cheung and Norde functions were used. The experimental result values of CuO/n-Si contact were compared with the values of the reference Cu/n-Si Schottky diode. It was observed that the values of the ideality factor and barrier height of the CuO/n-Si heterojunction were higher than those of the Cu/n-Si Schottky contact, while the series resistance was lower. Also, it has been observed that the value of capacitance decreased with increasing frequency and after a certain value of frequency it was almost constant. The ideality factor of CuO/n-Si/Al heterostructure is about 2.40 and so, it is not close to the ideal behavior.

Stibnite mineral (mainly Sb₂S₃) has been employed for the synthesis of tetrahedrite Cu₁₂Sb₄S₁₃ bulk material by spark plasma sintering. High purity Cu₁₂Sb₄S₁₃ can be quickly obtained by two sintering procedures at temperatures from the range of 420 °C to 440 °C for 1 h. Appropriate reduction of Cu content (Cu_12+xSb₄S₁₃, x ⩽ –0.05) or CuS content (Cu_12−ySb₄S_13−y, y = 0.1 or 0.3) was beneficial to fabricate Cu₁₂Sb₄S₁₃. The secondary resintering improved the purity of Cu₁₂Sb₄S₁₃ material. The first-order magnetic phase transformation with magnetic hysteresis effect was confirmed by the behavior of susceptibility, heat capacity and resistivity. The magnetization showed a linear increase with increasing field (up to 7 T) and non-saturation behavior was observed. The impurities in stibnite mineral Sb₂S₃ had a weak influence on the transformation temperature but affected the low-temperature magnetization value (~0.15, close to natural tetrahedrite). Similar transformation was observed by the analysis of heat capacity. The properties such as electrical resistivity, Seebeck coefficient and thermal conductivity were also measured for Cu_11:9Sb₄S₁₃ and Cu_11:9Sb₄S_12:9. The maximum figure of merit ZT of Cu_11:9Sb₄S_12:9 was 0.22 at 367 K.

The remote phosphor structure produces higher luminous flux but delivers poorer color quality than the conformal or in-cup phosphor structure. To eliminate this weakness, researchers have attempted to improve the chromatic properties of remote phosphor package. This study tends to enhance lighting features for WLEDs including color quality and luminous flux in general or color rendering index (CRI) and color quality scale (CQS) in particular by applying dual-layer remote phosphor structure. In the simulation section, we utilize two identical LEDs that only differ in correlated color temperature values which are 6600 K and 7700 K. The study offers an idea of placing a yellow-green phosphor layer SrBaSiO₄:Eu²⁺ or a red phosphor layer Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ on the yellow phosphor layer YAG:Ce³⁺ and then modifying the concentrations of Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ and SrBaSiO₄:Eu²⁺ to the suitable values to improve the color quality and lumen output of WLEDs. The results show that red phosphor layer Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ has a significant influence on CRI and CQS improvement. Particularly, the increase of Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ concentration leads to increased CRI and CQS because the red light component increases in WLEDs. On the other hand, the green phosphor layer SrBaSiO₄:Eu²⁺ only brings benefit to the luminous flux. However, the WLEDs’ luminous flux and color quality drop sharply, when Sr_wF_xB_yO_z:Eu²⁺,Sm²⁺ and SrBaSiO₄:Eu²⁺ concentrations rise extremely, which is verified based on the Mie-scattering theory and the Lambert-Beer law. In short, the article provides general knowledge and primary information for the production of higher-quality WLEDs.

The improved TiB₂ ceramics were obtained in sintering process at the pressure of 5.5 GPa and temperature of 1550 °C in presence of metallic Co powder. The effect of Co content (ranging from 0 wt.% to 10.0 wt.%) on the phase composition, density, microstructure, Vickers hardness and thermal conductivity of TiB₂ ceramics was analyzed. A small amount of new phase Co₂B has been created in the reaction of TiB₂ and Co. The relative density of sintered TiB₂ ceramics reached 98.1 %. When the mass fraction of Co increased, the porosity increased, while the hardness first increased and then decreased. The maximal Vickers hardness values were equal to 33.3 GPa or 28.2 GPa when the used load was of 4.9 N or 9.8 N, respectively. The highest reached value of thermal conductivity was 88.9 W˙m⁻¹ ˙ K⁻¹. The dense TiB₂ ceramics with improved hardness and thermal conductivity were ascribed to the high pressure sintering method and Co sintering aid. High pressure sintering method provides a new way for the preparation of ceramics materials.