EPR and optical studies on binary mixed alkali-alkaline earth oxide borate glasses doped with Cu<Superscript>2+</Superscript> ions

Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li₂O–xK₂O–12.5BaO–12.5MgO–49B₂O₃–1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X-ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calorimetry (MDSC) was used to determine the glass-transition temperature (T _g ). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramagnetic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of \(C{u^{2 + }}is{\kern 1pt} {d_{{x^2} - {y^2}}}\) orbital (²B_1g) and the site symmetry around Cu² is tetragonally distorted octahedral. The variation of g _|| and A _|| as a function of Li₂O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu² ions corresponding to ²B_1g → ²B_2g transition. From the optical absorption studies the values of the optical band gap (E _opt) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α², β² and β ₁ ² were evaluated.     

Optical Energy Estimation of Irradiated Polypropylene

The optical absorption has been studied under exposure to gamma radiation. Thin films of polypropylene were irradiated with a ⁶⁰Co source and doses ranged up to 6 kGy. Analysis of the optical absorption spectra indicated that both direct and indirect electron transitions take place in the polymer. The observed optical energy gap (E_opt) and energy gap-tail (ΔE) for irradiated films were determined from the measured absorption spectra. The average values of (E_opt) and (ΔE) are 5.85 eV and 0.5 eV, respectively. There is no detectable change in the optical energy gaps and tails under the applied gamma-ray doses.     

The optical band gap and the tailing states determination in glasses of TeO2-V2O5-K2O system

Ternary amorphous samples of 50TeO₂-(50 ? x)V₂O₅-xK₂O compositions with 0 ≤ x ≤ 20 (in mol %) have been prepared using the press-melt quenching method. The optical absorption spectra of glass have been recorded in the wavelength range 300–900 nm by UV-visible spectrophotometer. According to The Tauc and Urbach theories, the optical band gap and width of the tail of localized states have been evaluated. In addition the temperature glass transition (T _g ) of glasses have been determined by differential scanning calorimetry, confirming the amorphous nature of samples. The density and molar volume have been studied, indicating act of K₂O as network modifier.     

Optical Investigation of Sm<Superscript>3+</Superscript> Doped in Phosphate Glass

Samarium doped zinc-magnesium-phosphate glasses having composition (60 – x)P₂O₅–10MgO–30ZnO–xSm₂O₃ where x = 0.1, 0.3, 0.6, 1.0 mol % were prepared by melt quenching technique. Archimedes method was used to measure their densitieswhich are lying in the range 2.65–2.91 g/cm³. On the basis of the increasing trend in the density while increasing the content of Sm₂O₃ it can be concluded that the bridging oxygen is converted to non-bridging oxygen The UV-Vis absorption spectroscopy was carried on in the wavelength range 310–900 nm where the absorption spectra consist of six absorption peaks corresponding to the transitions from the ground state ⁶H_5/2 to various excited energy levels. The optical band gaps are calculated to be 3.93–4.41 eV, 3.31–3.73 eV and 0.27–0.29 eV for direct band gap, indirect band gap and Urbach energy, respectively. The physical parameters like oxygen packing density, refractive index, molar refractivity, metallization, and electronic polarizability are also studied. The Differential Scanning Calorimetry (DSC) technique is used to evaluate the thermal stability.     

Catalytic combustion of methane over M (Ni,Co, Cu) supported on ceria–magnesia

The catalytic activity of a series of M(= Ni, Co, Cu)/(CeO₂)_x–(MgO)_1 − x catalysts for methane combustion was investigated. (CeO₂)_x–(MgO)_1 − x supports were prepared by a sol-gel method. The influence of CeO₂ content and active components such as Ni, Co and Cu are discussed. The results indicate that the activity of the catalysts depends strongly on CeO₂ content. The Ni/(CeO₂)_0.1 − (MgO)_0.9 catalyst showed the highest catalytic activity and good thermal stability for methane combustion. The highly dispersed NiO is the main active site for methane combustion. Fresh M (Ni, Co and Cu)/(CeO₂)_0.1–(MgO)_0.9 catalysts showed that the activity of CuO for methane combustion was slightly higher than that of NiO and CoO, while the thermal stability increased in the order Cu < Co < Ni. Cu/(CeO₂)_0.1–(MgO)_0.9 catalyst was sintered after a second evaluation. Consequently, (CeO₂)_0.1–(MgO)_0.9 is deemed to be a good support for Ni.     

Emission analysis of CdO–Bi2O3–B2O3 glasses doped with Eu and Tb

This article reports on the emission properties of cadmium bismuth borate (CdBiB) glasses as a function of doping concentrations of Eu³⁺ and Tb³⁺ ions. The functional groups present in the glasses have been identified by analyzing FT-IR spectra. The emission spectra of Eu³⁺ and Tb³⁺:CdBiB glasses have shown reddish green emissions at 616 nm (⁵D₀→⁷F₂) under the excitation at 465 nm and at 547 nm (⁵D₄→⁷F₅) under the excitation at 485 nm, respectively. The Judd–Ofelt (J–O) theory was applied to evaluate the J–O intensity parameters from the absorption and the emission spectra; by using the J–O intensity (Ω_λ) parameters, spontaneous emission transition probability (A), total radiative transition rate (A_T), radiative lifetime (τ_R) and branching ratios (β) of the various emission transitions have been computed for both Eu³⁺ and Tb³⁺:CdBiB glasses. The quenching behavior in the emission intensity with increased concentration of Eu³⁺ and Tb³⁺ was observed, which could be useful for optimizing the compositions toward practical applications.     

Preparation and characterization of nanocrystalline La-doped ZnO powders through a mechanical milling and their optical properties

Structural and optical properties of mechanically milled La-doped ZnO powders are presented in this paper. The Zn_1−xLa_xO phase formed when x varied in a range of 0.02-0.06 and milled at 400 rpm for 20 h. The secondary La₂O₃ phase occurred with an increase of La content. The crystallite and particle size decreased as a function of La content as x = 0-0.14 due to the effect of Zener pinning and solute drag. The absorption edge shifted to a lower wavelength when La content was increased to x = 0.14 because of the size effect. The energy band gap of Zn_1−xLa_xO powders varied in a range of 2.96-3.12 eV depending on the crystallite size. The broad emission bands in a visible region centered at about 640 nm are attributed to oxygen deficiency.     

Effect of Li<Subscript>2</Subscript>O on the Refractive Index and Optical Band Gap of Cadmium Phosphate Glasses

A series of lithium cadmium phosphate glasses having composition (mol %) xLi₂O-(50 ? x)CdO-50P₂O₅ were prepared in a platinum crucible by the melt quenching technique. The quantity x varies in the range 0–40. The mass density and refractive index of these glasses were found in the ranges 3.95–2.89 g/cm₃ and 1.55–1.40, respectively. The optical absorbance studies were also carried out on these glasses to measure their energy gaps. The absorption spectra of these glasses were recorded in the UV-visible range. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range 2.58–3.5 eV. It was observed that the density, the refractive index, and the optical band gap energy decrease with increasing amount of lithium oxide. The band tailing, worked out from the Urbach plots, shows an increase with increasing Li₂O content and lies in the range 0.47–0.78 eV. The absorption coefficient is observed to show an exponential dependence on the photon energy.     

Wavelength and temperature dependences of the absorption and scattering cross sections of soot

We have inferred the wavelength and temperature dependence of the absorption and scattering cross sections of mature soot in an ethylene flame from laser-induced incandescence (LII) and transmittance measurements at 532 and 1064 nm. The LII measurements indicate that the emissivity of soot in a flame deviates from the expected 1/λ dependence. Combining the LII results with transmittance measurements yields single-scattering albedos of 0.058-0.077 at 1064 nm and 0.22-0.29 at 532 nm and values of F(m)/E(m) of 2.2-2.9 at 532 nm and 2.4-3.3 at 1064 nm. These values confirm that scattering must be taken into account when interpreting extinction data at these wavelengths. Our results also indicate increases in the absorption cross section and decreases in the scattering cross section with increasing fluence at low fluences. The increase in absorption cross section is consistent with increases in primary particle size with increasing particle temperature during laser heating. The decrease in scattering cross section could be attributable to an increase in the radius of gyration or a decrease in the fractal dimension of the aggregate with increasing temperature. Alternatively these trends might be the result of changes to the optical properties of the particles with increasing temperature.     

Structure,dielectric and optical properties of Bi1.5+xZnNb1.5O7+1.5x pyrochlores

Non-stoichiometric pyrochlore ceramics with formula Bi_1.5+xZnNb_1.5O_7+1.5x were systematically investigated. Crystal structures of the compounds were studied by X-ray diffraction (XRD) technique. The structures were identified as pure cubic pyrochlores when |x| < 0.1. Dielectric and optical properties of the compositions when x = −0.1, 0 and 0.1 were studied. All samples have high resistivities and low dielectric loss. With increasing x in Bi_1.5+xZnNb_1.5O_7+1.5x, the lattice constant, permittivity, temperature coefficient of permittivity and thermal expansion coefficient increased, while dielectric loss decreased. Raman spectra indicated that the intensity of Bi–O stretching become stronger with increasing x. A vibration mode emerging at 861 cm⁻¹ when x = −0.1 means that the B–O coordination environment is significantly more disordered. Absorption spectra suggested that the bandgap energy become lower from 2.86 to 2.70 eV as lattice constants increased. Strong absorption occurs at wavelengths from 433 to 459 nm, shows that samples have the ability to respond to wavelengths in the visible light region.     

Isothermal crystallization kinetics and effect of crystallinity on the optical properties of nanosized CeO2 powder

The isothermal crystallization kinetics and effect of crystallinity on the optical properties of cerium dioxide (CeO₂) nanopowders synthesized using a coprecipitation route at 293 K and pH 9 were investigated using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and ultraviolet–visible absorption spectrophotometry. The activation energy of CeO₂ crystallization from dried cerium dioxide precursor powders by isothermal method of 64.1±3.24 kJ/mol was obtained. The average value of the growth morphology parameter (n) is 1.94, meaning that two-dimensional growth with plate-like morphology was the primary mechanism of CeO₂ crystallization from cerium dioxide precursor powders. The indirect band gap energy (E_i) of CeO₂ decreased from 3.03 eV to 2.83 eV when the crystallinity increased from 18% to 82%, and the direct band gap energy (E_d) of CeO₂ also decreased from 3.76 eV to 3.64 eV.     

Structural and optical characterization of Zn0.95−xMg0.05AlxO nanoparticles

The structural and optical properties of ZnO nanoparticles doped simultaneously with Mg and Al were investigated. XRD results revealed the hexagonal wurtzite crystalline structure of ZnO. The FE-SEM study confirmed the formation of nano-sized homogeneous grains whose sizes decreased monotonously with increasing doping concentrations of Mg and Al. The absorption spectra showed that band gap increased from 3.20 to 3.31 eV with Mg doping. As the Al concentration changed from x=0.01 to x=0.06 mol% at constant Mg concentration the band gap observed to be decreased. Particle sizes estimated from effective mass approximation using absorption data and these values are in good agreement with the crystallite sizes calculated from XRD data. Raman spectra of ZnO showed a characteristic peak at 436 cm⁻¹ correspond to a non-polar optical phonon E₂ (high). With increase of the Al doping concentrations, E₂ (high) phonon frequency shifted to 439 cm⁻¹ from to 436 cm⁻¹. The origin of E₂ (high) peak shift in ZnO nanoparticles is attributed to optical phonon confinement effects or the presence of intrinsic defects on the nanoparticles. PL spectra indicated that with increase of Al co-doping along with Mg into ZnO, intensity of the peak positioned at 395 nm was initially increased at x=0 and then decreased with increase of the Al concentrations from x=0.01 to x=0.06 mol%.     

Stable anatase phase with a bandgap in visible light region by a charge compensated Ga–V (1:1) co-doping in TiO2

A series of charge compensated Ga–V co-doped TiO₂ samples (Ti_(1-x)(Ga_0.5V_0.5)_xO₂) have been synthesized by a modified sol-gel process. X-ray diffraction pattern shows that the anatase to rutile (A→R) onset temperature (T_O) shifts to a higher temperature, whereas the complete phase transformation temperature (T_C) shifts to a low-temperature region as compared to pure TiO₂, due to Ga–V incorporation. Ga–V co-doping helps in the transformation of some smaller sized Ti⁴⁺ to a relatively larger Ti³⁺. In the anatase phase, oxygen content also increases with increasing doping concentration, which along with the larger size of Ti³⁺ results in lattice expansion and thereby delays the T_O. In the rutile phase, oxygen vacancy increases with increasing doping concentration, which results in lattice contraction and accelerates phase transition. Grain growth process is hindered in the anatase phase (crystallites size reduces from ~15 nm (x = 0.00) to 8 nm (0.10)), whereas it is accelerated in the rutile phase as compared to pure TiO₂. In both phases bandgap (E_g) reduces to the visible light region (anatase: E_g = 3.16 eV (x = 0.00) to 2.19 eV (x = 0.10) and rutile: 3.08 eV (x = 0.00) to 2.18 eV (x = 0.10)) in all co-doped samples. The tail of the absorption edge reveals lattice distortion and increase of Urbach energy proofs the same due to co-doping. All these changes (grain growth, phase transition, and optical properties) are due to lattice distortion created by the combined effect of substitution, interstitials, and oxygen vacancies due to Ga–V incorporation in TiO₂.     

Temperature annealing of radiation defects in xCu2Se-(1 − x)As2Se3 glasses: Dependence on composition

The temperature annealing of radiation defects (RDs), which are broken bonds of network atoms, has been studied for a number of glasses of quasi-binary system xCu₂Se-(1 ? x)As₂Se₃ γ-irradiated at 77 K. The density distributions of localized states caused by defects have been determined based on the temperature dependences of the relative intensity I(T)/I(77) of the EPR spectrum of RDs and according to the energy of the thermal release of D(E); and it was found that their shape is close to Gaussian. There is a significant shift in the curves of I(T)/I(77) to lower temperatures with increasing Cu content in the network. In glasses with copper, the width of D(E), and the density of localized states increase with increasing x. It is assumed that the dependence of E ^m (x) (E ^m —energy, which corresponds to the maximum of the distribution of D(E)), correlates with the change in the negative effective interelectron correlation energy U _eff on x. In As₂Se₃ glasses, in the temperature range of 77 to ～175 K, values of I(T)/I(77) > 1 are observed, which was explained by the appearance of thermally induced defects.     

Morphological,structural and ellipsometric investigations of Cr doped TiO2 thin films prepared by sol–gel and spin coating

Pure and chromium doped titanium dioxide (TiO₂) thin films at different atomic percentages (0.5%, 1.3% and 2.9%) have been elaborated on ITO/Glass substrates by sol–gel and spin–coating methods using titanium (IV) isopropoxide as a precursor. The surface morphology of films was investigated by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM), the structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission microscopy (HRTEM). SEM and HRTEM show homogenous and polycrystalline films. XRD patterns indicate a phase transition from anatase to anatase-rutile leading to expand the absorption band of TiO₂ molecules around 520 cm⁻¹ in FTIR spectra. The optical constants such as the refractive index (n), the extinction coefficient (K) and the band gap (E_g) as well as the film thickness are determined using spectroscopic ellipsometry technique and Fourouhi–Blommer dispersion model. Results show three major changes; (i) the thickness of pure TiO₂ layer is 54 nm, which linearly decreases when the layer is doped with chromium and reaches 33 nm for a doping concentration of 2.9%, (ii) the band gap energy (E_g) is also linearly reduced from 3.24 eV to 2.80 eV when the Cr-doping agent increases, and, (iii) a phase transition from anatase to anatase-rutile is observed causing an increase in values of n(λ) for wavelength greater than 350 nm.     

Thermal desorption of deuterium from modified carbon nanotubes and its correlation to the microstructure

The process of deuterium desorption from single-wall carbon nanotubes (SWNTs) modified by atomic (D) and molecular (D₂) deuterium treatment was investigated in an ultrahigh vacuum environment using thermal desorption mass spectroscopy (TDMS). Microstructural and chemical analyses of SWNT material, modified by this deuterium interaction, were performed by means of a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results disclose characteristic features in the TDMS spectra of deuterium evolved from the SWNT material, which can be correlated to the microstructure of nanocarbon material modified by D-treatment. The TDMS spectra of deuterium originating from the large diameter rope type nanotube structures, resulting from a prolonged low-pressure (D + D₂) gas mixture treatment, exhibit three overlapping desorption peaks: a dominant one with a desorption activation energy (E_des) of approx. 2.86 eV and lower intensity peaks at E_des of ∼1.50 and 2.46 eV. On the other hand, the TDMS spectra of deuterium taken from the “coral reef”-like carbon nanostructures, obtained after prolonged treatment of SWNTs to a high-pressure (D + D₂) gas mixture produced at high temperature, reveal the coexistence of four superimposed desorption peaks with E_des ranging from 1.23 to 4.4 eV. A dominant desorption peak with E_des ≈ 4.4 eV, can be attributed to bulk diffusion of D trapped within this nanocapsule bulk structure.     

Effect of Zr ions on the structure and optical properties of lithium borosilicate molybdate glass system

The glass system with the composition [(20-x) MoO₃– x ZrO₂–15 SiO₂– 65 Li₂B₄O₇, x = 0, 1, 2, 3, 4, and 5 mol %] was successfully synthesized using the melt quenching method. The XRD results of this glassy system confirmed the glassy nature of the prepared glasses. The density of this glassy system presented higher values while the molar volume provided lower values with increasing ZrO₂ content. The FTIR result showed that the spectrum of each sample consisted of broad bands that de-convoluted into several peaks. These peaks were characterized and the structure of each sample was recognized. Additionally, the optical measurements showed that sample x = 0 mol% provided a sharp ultra-violet cut-off at 380 nm, while the other samples showed a transition peak in the (210–230) nm range. The energy of optical band gaps of these glass samples decreased and the Urbach energy increased by increasing ZrO₂ content. Moreover, the different optical parameters of these glass samples were calculated and showed that the studied glasses could be considered promising materials to be used in different optical applications such as nonlinearity and optoelectronics.     

Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO₂) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as the starting material. The growth and optical properties of nanosized CeO₂ powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO₂ precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO₂. In the dried precursor powders, the crystallites of CeO₂ measured 10.4 nm and 66.8 nm before and after calcination at 1273 K for 240 min, respectively. The indirect band gap energy (_Ei$E_i$) of CeO₂ decreased from 3.03 eV to 2.68 eV as the crystallite size increased from 10.4 nm to 66.8 nm, whereas the direct band gap energy (_Ed$E_d$) of CeO₂ also decreased from 3.79 eV to 3.38 eV.     

Effect of Gamma Irradiation on Structural and Optical Investigations of Borosilicate Glass Doped Yttrium Oxide

The structural, physical, and optical properties of prepared glass samples of the composition formula 30SiO₂-(40-x)B₂O₃-20Na₂O-10Al₂O₃-xY₂O₃, where x = 0, 1, 5, 7 (wt%) were studied before and after gamma irradiation using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-visible spectroscopy. The optical absorption spectra of study glasses were recorded in the UV/visible range of 200–900 nm. The optical band gap energies were calculated from absorption data. These results show that E_opt decreases with increasing concentration of Y₂O₃. The changes occurring in the optical parameters obtained from absorption spectra before and after irradiation have been referred to irradiation induced structural defects and compositional changes.     

Optical Properties of Silver Halide Photochromic Glasses Doped with Cobalt Oxide

Photochromic glasses having composition (SiO₂)₄₅(B₂ O ₃)₃₅(Al₂O₃)_7.5(Na₂O)_12.5(AgBr), (Cu₂O) doped with (CoO) _x , in which, x = 0, 0.006, 0.02 and 0.07 g were prepared using the conventional melt technique. The amorphous nature of these glass samples was confirmed using X-ray diffraction analysis at room temperature. The absorption measurements in the infrared region of the spectrum were recorded in the wave number range (4000–400) cm^?1. Spectral reflectance and transmittance at normal incidence of the prepared glass samples were recorded with a spectrophotometer in the spectral range 200–2500 nm. Experimental and theoretical densities of the prepared glass samples were measured, calculated and compared. Analytical expressions were used to calculate the real and imaginary parts of the refractive indices. Dispersion parameters such as: single oscillator energy, dispersion energy, average oscillator wavelength, and Abbe’s number were deduced and compared. Absorption dispersion parameters such as: optical energy gap for direct and indirect transitions, Urbach energy and steepness parameter were calculated. Effects of doping with cobalt oxide CoO as a transition metal on linear and predicted nonlinear optical parameters were investigated and interpreted. Experimental results indicate that there is an optimum concentration of cobalt doping around 0.006 g. The optical band gap decreases with increasing doping and causes an increase in nonlinear optical parameters. Doping with cobalt oxide improves the linear and nonlinear optical properties of the prepared glasses.