Optical parameters and absorption studies of UV‐irradiated azo dye‐doped PMMA films

PMMA and PMMA films doped with different contents of azo dye have been made by using the casting technique. The absorption spectral analysis showed that the doped films have two absorption bands attributed to the π‐π* and n‐π* transition of chromophore groups. These bands disappear upon UV‐irradiation, suggesting that the studied system undergoes a photo degradation process. The absorption coefficient and optical energy gap (E_g) have been obtained from the absorption edge in the 200–900 nm range. It was found that E_g decreases with increasing doping levels, whereas it increases with increasing irradiation time. The width of the tail of localized states in the band gap (ΔE) was evaluated using the Urbach edge method. Some optical parameters were determined from the reflection and transmission spectra in the spectral range of 200–2500 nm. The dependence of the refractive index on irradiation time and doping level have been discussed. It was found that the photo‐induced refractive index changes are very large. These changes suggest the applicability of the studied system in optical devices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystal Structure and Physical Properties of PVDF Films Filled with CuCl2–MnCl2 Mixed Fillers

ABSTRACT

Poly(vinylidene fluoride) (PVDF) films filled with mixed fillers of CuCl₂–MnCl₂ were prepared. The differential thermal analysis (DTA) indicates the existence of two main endothermic peaks and the crystallization exothermic temperature. X-ray diffraction (XRD) evidenced the presence of a semicrystalline structure containing α, β, and γ crystalline phases. The optical absorption spectra depicted two shoulder-like bands as well as a strong valley. The IR spectra confirmed the XRD implications about the presence of α, β, and γ phases. The dc electrical resistivity results are discussed on the basis of Kuivalainen modified interpolaron hopping model. The temperature and filling level dependence of the hopping distance R₀ were studied. The dc magnetic susceptibility data follow the Curie-Weiss law. The electron spin resonance (ESR) investigation suggested the existence of aggregated Mn²⁺ for higher values of x where the spectra were characterized by Lorentzian signal. On the other hand, at lower values of x, the spectra were characterized by two unresolved sharp peaks.     

Dilute magnetic semiconductor of ZnCoSe thin films: Structural,optical, and magnetic characteristics

A series of Zn_1−xCo_xSe (x = 0, 0.025, 0.050, 0.075, and 0.100) films using were evaporated (thickness of 1 μm) using electron beam gun. The effect of Co doping on the structural, optical, and magnetic properties has been investigated. X-ray diffraction studies confirm formation of zinc blend structure for all Zn_1−xCo_xSe films. The crystallite size increases and the lattice strain decreases with the increase in Co content. The elemental constituents were characterized by energy dispersive X-ray. Optical studies showed an increase in refractive index and a decrease in energy gap with the increase in the cobalt doping. The dispersion of the refractive index has been analyzed in terms of the Wemple-DiDomenico single oscillator model. The oscillator parameters including the single oscillator energy (E_o), the dispersion energy (E_d), and the static refractive index (n₀) were estimated. Magnetization measurements via vibrating sample magnetometer showed a hysteresis loop and confirmed room-temperature ferromagnetism in Co-doped ZnSe films.     

Dispersion parameters of cadmium chloride doped PVA-PVP blend films

Solution cast films of poly vinylalcohol (PVA) – poly vinylpyrrolidone (PVP) polymer blend, doped with different concentrations (from 0.5 wt% up to 40 wt%) of cadmium chloride (CdCl₂) have been studied by analysing the data recorded using optical (UV-Vis) spectrometry. The modified band structure of PVA -PVP blends doped with CdCl₂ has been studied using Moss model and Wemple - DiDomenco model. Optical parameters such as transmittance (T), reflectance (R), refractive index (n), average oscillator energy (E₀), oscillator dispersion energy (E_d), real and imaginary part of dielectric constant (ε_r and ε_i) have been determined. The ratio of charge carrier concentration to effective mass (N/m^*), plasma frequency (ω_p), average oscillator wavelength (λ_o), oscillator strength (S_o), optical conductivity (σ) and optical momenta of spectra (M_?1 and M_?3) have been estimated for the PVA-PVP blend films doped with CdCl₂.     

Influence of Heat Treatment on the Optical Properties of Thermal Evaporated SnO<Subscript>2</Subscript> Thin Films

In this investigation, the optical properties of the thermally evaporated SnO₂ films and their dependence on the heat treatment were studied. The transmittance, T (λ), spectra were measured over the spectral range of 0.2 to 0.8 μm for SnO₂ films that were annealed at different temperatures (300, 350, 400, 450, 500, 550 and 600 K) in vacuum for 1h. All films showed high transparency in the visible range and increased with increasing the wavelength. These films have become more transparent after annealing at different temperatures. The optical constants of annealed SnO₂ films were obtained by modeling the measured transmission spectra. The best fit modeling of transmission spectra was obtained by applying Drude and OJL models combined with the effective medium approximation Bruggeman model. Increasing the annealing temperatures decreased both the refractive index and the extinction coefficient of the films. While the optical band gap energy increased from 3.05 to 4.11 eV by increasing the annealing temperature from 300 to 600 K, respectively. Analyzing the refractive index dispersion by using the Wemple-DiDomenico model revealed that the oscillator resonance energy E_o decreased whereas the oscillator dispersion energy E_d increased with increasing the annealing temperature.     

Electronic structure of poly(p-phenylene sulfide)

The electronic structure of poly(p-phenylene sulfide) (PPS) was studied through steady state photocurrent spectra and temperature dependence of dark conductivity for undoped film, by changes in the in situ optical absorption and ESR spectra under photoirradiation, and optical absorption spectra for doped film. The charge carriers in the undoped state are electronic since the photoconductivity is large and the kink point in the temperature dependence of dark conductivity is higher than the glass transition temperature. A sharp peak near the absorption edge in the photocurrent spectrum of undoped PPS is caused by the diffusion of photocarriers in a sheet with high surface recombination under conditions of low applied field. The in situ optical absorption and ESR spectra of SO₃-doped PPS were similar to those of di-p-tolyl sulfide (a monomer unit of PPS) and the formation of sulfur-centered radical cations was suggested rather than bipolaron states. The stable conduction of SO₃-doped PPS after exposure to atmosphere was analyzed by the classical Lorentz model and the existence of nearly free carriers within subchains was suggested. Their conductivity and mobility were estimated to be 2 S/cm and 3.6 cm²/Vs, respectively. Inter-chain conduction appears to be very low.     

Optical properties of alkali and alkaline-earth lead borate glasses doped with Nd<Superscript>3+</Superscript> Ions

Spectroscopic and physical properties of Nd³⁺-doped alkali lead borate glasses of type 20R ₂O · 30PbO · 49.5B₂O₃ · 0.5Nd₂O₃ (R = Li and K) and alkaline-earth lead borate glasses 20RO · 30PbO · 49.5B₂O₃ · 0.5Nd2O3 (R = Ca, Ba, and Pb) have been investigated. Optical absorption spectra have been used to determine the Slater-Condon (F₂, F₄, and F₆), spin orbit ξ_4f, and Racah parameters (E₁, E₂, and E₃). The oscillator strengths and the intensity parameters Ω₂, Ω₄, and Ω₆ have been determined by the Judd-Ofelt theory, which, in turn, provide the radiative transition probability (A), total transition probability (A _T ), radiative lifetime (τ _R ), and branching ratio (β _R , %) for the fluorescent levels. The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Ω₄/Ω₆), the value of which is in the range 0.2–1.5, typical of Nd³⁺ in different laser hosts. A red shift of the peak wavelength is observed upon addition of alkali or alkaline-earth oxides to the lead borate glass. A higher value of the W₂ parameter for potassium-doped glass indicates a higher covalency for this glass matrix. The relative intensity of the peaks ⁴I_9/2 → ⁴F_7/2, ⁴S_3/2 has also been studied. The text was submitted by the authors in English.     

UV–VIS absorption and NIR‐stimulated emission of Nd3+: PVA films

Neodymium‐doped polyvinyl alcohol films were prepared and the optical properties of the films were investigated. By applying Judd–Ofelt theory, the Ω parameters were obtained from the absorption spectrum. Various radiative parameters like transition probability for each level (A_J), total transition probability (A_T), branching ratio (β_R), radiative lifetime (τ_rad), and absorption cross‐section (σ_A) were calculated. The theoretically obtained branching ratio and integrated absorption cross‐section are found to be greater for the transition ⁴F_3/2 → ⁴I_11/2. From the emission spectrum peaked at 1064‐nm stimulated emission cross‐section (σ_E), the line width (Δλ_eff) is calculated to be 6.21 × 10^?21 cm² and 41 nm, respectively. Further the variation of the optical gain with the length of the film was studied and the slope efficiency (η = 8.5%) was determined from laser measurements. These results clearly support the potentiality of the Nd³⁺: polyvinyl alcohol films in realizing optical amplification and stimulated emission. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of valence electron spin polarization on the physical properties of CuCl2‐filled poly(vinylidene fluoride) as a microwave modulator

Infrared and optical spectra, differential thermal analysis, dc electrical resistivity, magnetic susceptibility, electron spin resonance, and microwave response of CuCl₂‐filled poly(vinylidene fluoride) (PVDF) films, over the filler mass fraction range 0.05 ≤ W ≤ 0.4, were measured. The infrared spectra evidenced the presence of β‐phase, for all of the filler levels with main deformations of 20% (for W = 0.25) and 30% (for other filler levels) head‐to‐head and tail‐to‐tail units, which were considered as polaron and bipolaron defects. Optical activity was mainly influenced by PVDF structure. Differential thermal analysis revealed dipole relaxation and premelting endothermic peaks. A quasi–one‐dimensional interpolaron hopping was thought to proceed in the direct current electric conduction, with a hopping distance less than the distance between two successive head‐to‐head sites. A temperature‐independent Pauli paramagnetic behavior was observed, confirming the presence of induced energy bands due to CuCl₂ filling. Most of the observed electron spin resonance signals were antisymmetric, with superimposed repels due to the hyperfine interactions characterizing PVDF. The obtained linear dependence of the isotropic hyperfine coupling constant (ΔA` ), for Cu(II), on average g‐factor, implied that ΔA` is a measure of the valence electron spin polarization. An octahedral or distorted octahedral configuration was suggested for Cu(II). The present system is a good microwave modulator. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 771–781, 1999     

Photoluminescence and Temperature Dependent Electrical Properties of Er‐Doped 0.94Bi0.5Na0.5TiO3‐0.06BaTiO3 Ceramics

Er‐doped 0.94Bi_0.5Na_0.5TiO₃‐0.06BaTiO₃ (BNT‐6BT: xEr, x is the molar ratio of Er³⁺ doping) lead‐free piezoceramics with x = 0–0.02 were prepared and their multifunctional properties have been comprehensively investigated. Our results show that Er‐doping has significant effects on morphology of grain, photoluminescence, dielectric, and ferroelectric properties of the ceramics. At room temperature, the green (550 nm) and red (670 nm) emissions are enhanced by Er‐doping, reaching the strongest emission intensity when x = 0.0075. The complex and composition‐dependent effects of electric poling on photoluminescence also have been measured. As for electrical properties, on the one hand, Er‐doping tends to flatten the dielectric constant‐temperature (ε_r‐T) curves, leading to temperature‐insensitive dielectric constant in a wide temperature range (50°C–300°C). On the other hand, Er‐doping significantly decreases the ferroelectric‐relaxor transition temperature (T_F–R) and depolarization temperature (T_d), with the T_F–R decreasing from 76°C to 42°C for x = 0–0.02. As a result, significant composition‐dependent electrical features were found in ferroelectric and piezoelectric properties at room temperature. In general, piezoelectric and ferroelectric properties tend to become weaker, as confirmed by the composition‐dependent piezoelectric coefficient (d₃₃), planar coupling factor (k_p), and the shape of polarization‐electric field (P–E), current‐electric field (J–E), bipolar/unipolar strain‐electric field (S–E) curves. Furthermore, to understand the relationship between the T_F–R/T_d and the electrical properties, the composition of x = 0.0075 has been intensively studied. Our results indicate that the BNT‐6BT: xEr with appropriate Er‐doping may be a promising multifunctional material with integrated photoluminescence and electrical properties for practical applications.     

Physical properties and β-phase increment of AgNO3-filled poly(vinylidene fluoride) films

X-ray diffraction (XRD), infrared (IR) transmition and optical absorption (OA) spectra, differential thermal analysis (DTA), dc electrical resistivity (ρ), magnetic susceptibility (χ) and electron spin resonance (ESR) of AgNO₃-filled poly(vinylidene fluoride) (PVDF) films, were measured over the filler mass fraction range 0.001 ≤ W ≤ 15%. XRD and IR analysis evidenced the increase of α- and β-PVDF crystalline phases due to the AgNO₃ filler. The maximum crystallinity increment was found at W = 0.5%. Three endothermic peaks were detected by DTA, and were attributed subsequently to: the first order para–para-electric phase transition, the first-order ferro-para-electric phase transition and the melting. The melting peak was used to calculate the order of reaction and the activation energy of melting. The observed OA peaks and/or plateau were attributed to the charge-transfer complex formed mainly by the AgNO₃ filler. This assumption was supported by the diamagnetic susceptibility detected for the present system. The temperature dependence of ρ was explored according to a previously proposed one-dimensional interpolaron-hopping model. The hopping distance was formulated numerically as a function of temperature and filling level. The ESR findings were attributed to the roles of AgNO₃ and dimethylformamide solvent in complex formation. Copyright © 2004 Society of Chemical Industry     

Study on the effect of acid‐ or iodine‐doping on the properties of copolymer C1–4poly‐phenylene‐vinylene‐ether

In this article, the new red‐colored copolymer, referred to as C_1–4poly‐phenylene‐vinylene‐ ether (C_1–4PPV‐ether) is built as a PPV polymer with some conjugated links (? CH?CH? ) that are changed into ethylic‐ether links (? CH₂? O? CH₂? ) and whose modified phenyl ring is grafted, respectively, in two and five positions with methoxy and butoxy groups. The C_{1– 4}PPV‐ether is doped with protonic acid or iodine. The infrared absorption (IR), optical density, X‐ray photoelectron spectroscopy (XPS), and electron spin resonance (ESR) show that there is a charge transfer complex formed between the copolymer and the doping species (iodine or acidic dopants). From IR, XPS, and ESR analysis, we deduced that the doping mechanism of the copolymer is, respectively, a protonation of the double links in PPV in the case of the protonic acid doping process and a grafting of the iodine to the ether links in the case of iodine‐doping process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1858–1866, 2002     

Mechanism of proton doping in polyaniline

The protonation processes of polyaniline (PANI) were examined by means of both UV-visible and fluorescence spectra and in situ UV-visible and in situ electron spin resonance (ESR) spectra in order to understand he mechanism of proton doping in PANI. Results obtained from UV-visible and fluorescence spectra of PANI films indicate that the protonation processes take place on the imine segment of the polyemerldine chain consistent with MacDiarmid's suggestions. It is noted that the protonation processes consist of chemical and diffusion processes. The doping processes at the initial stage are controlled by a chemical reaction, whereas the doping processes at the middle period are dominated by a diffusion process. In situ ESR spectra of PANI films have demonstrated that a polaron is formed after protonation processes, but a splitting process of bipolaron into polaron at the measured time region was not observed. For partial protonated PANI, moreover, the fact that variation of absorption value of the peak at 630 nm with doping time supported suggestions in which a parameter of the protonation state for the molecular structure of doped PANI should be considered. © 1995 John Wiley & Sons, Inc.     

Study of miscibility enhancement in poly(styrene‐co‐4‐vinylphenol)/poly(ethylene oxide) blends by the spin labelling method

The electron spin resonance (ESR) spectra of end‐group spin labelled poly(ethylene oxide) (SLPEO) using 2,2,6,6‐tetramethyl‐piperdine‐1‐oxyl nitroxide and its blends with poly(styrene‐co‐4‐vinylphenol) (STVPhs) of different hydroxyl contents were recorded over a wide temperature range. For a blend of SLPEO and pure polystyrene (PS), the ESR spectrum was composed of a single motion component, indicating that PS was immiscible with PEO. For blends composed of SLPEO and different‐hydroxyl‐content STVPhs, two spectral components with different motion rates were observed over a certain temperature range. The difference between the motion rates should be attributed to micro‐heterogeneity in the blends, with the faster rate corresponding to a nitroxide radical motion trapped in the PEO‐rich domain and the slower rate corresponding to a nitroxide radical motion trapped in the STVPh‐rich domain. Variations in the values of a number of the ESR parameters (T_a, T_d and T_50G) and the apparent activation energy (E_a) with hydroxyl content in the blends indicated that the miscibility of the blends increased with increasing hydrogen‐bonding density due to specific interactions between the hydroxyl groups in STVPh and the ether oxygens in PEO. Copyright © 2004 Society of Chemical Industry     

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%.     

Optical and colorimetric studies of thorium nitrate‐doped poly(vinyl alcohol) films

In this study, poly(vinyl alcohol) (PVA) films doped with thorium nitrate hydrate [Th(NO₃)₄] have been prepared using casting technique. The optical absorption spectra were recorded at room temperature in the wavelength range 200–800 nm. From the absorption edge studies, the values of the Urbach energy (E_u) have been evaluated. These energy values vary slightly with composition, indicating that the model based on electronic transitions between localized states is not preferable. Optical parameters such as refractive index and complex dielectric constant have been determined. The dispersion of the refractive index is discussed in terms of the single‐oscillator Wemple‐DiDomenico model. Color properties of the prepared samples were discussed in the framework of CIE L*u*v* color space. POLYM. COMPOS., 35:1786–1791, 2014. © 2013 Society of Plastics Engineers     

Electron spin resonance and ultraviolet spectral analysis of UV‐irradiated PVA films filled with MnCl2 and CrF3

PVA films with various filling levels of CrF₃ and MnCl₂ were prepared. ESR and UV/VIS optical analysis were used to shed more light on the structural modification that occur due to filling with different levels and/or UV irradiation. The ESR analysis revealed that the spin configuration of CrF₃, MnCl₂, and CoBr₂‐filled PVA are different. The filling level dependence of ESR parameters was discussed. The UV‐VIS spectral analysis for pure PVA shows absorption bands at 265 and 280 nm, which were assigned to the presence of carbonyl groups. The addition of CrF₃ led to the appearance of another bands at 418 and 596 nm. The filling level and/or UV irradiation have no effect on the position of absorption bands but the intensity of these bands has been changed. The addition of MnCl₂ led to a new band at about 350 nm due to charge transfer transition. The ligand field parameters and optical energy gaps can be calculated and discussed. The results of optical and ESR analysis indicated that the Cr³⁺ or Mn²⁺ are present in its octahedral symmetrical form within the PVA Matrix. SEM micrographs of CrF₃ filled PVA is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 104–111, 2003     

Self‐organized MEH‐PPV domains in a TPU matrix and the consequences to the luminescence spectra

Self‐sustained cast films formed from heterogeneous blends of poly(2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV) conjugated polymer and thermoplastic polyurethane (TPU) were investigated by photoluminescence (PL) and scanning electron microscopy (SEM). A blue shift is observed for the pure electronic transition PL peak (E₀₀) with decreasing MEH‐PPV concentration. The two clear shoulders in the PL spectra at higher energy than the E₀₀ peak appear due to the formation of small conjugation segments of the MEH‐PPV molecules at the interface of the spherical MEH‐PPV domains. This assumption and the origin of the blue shift were confirmed by correlating the average size of the MEH‐PPV domains, observed from SEM images, and the analysis of the PL spectra at low temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radical polymerization behavior of dimethyl vinylphosphonate: Homopolymerization and copolymerization with trimethoxyvinylsilane

Dialkyl vinylphosphonates such as dimethyl vinylphosphonate (DMVP) and diethyl vinylphosphonate were quantitatively polymerized with dicumyl peroxide (DCPO) at 130°C in bulk. The polymerization of DMVP with DCPO was kinetically studied in bulk by fourier transform near‐infrared spectroscopy (FTNIR) and electron spin resonance (ESR) spectroscopy. The initial polymerization rate (R_p) was given by R_p = k[DCPO]^0.5[DMVP]^1.0 at 110°C, being the same as that of the conventional radical polymerization involving bimolecular termination. The overall activation energy of the polymerization was estimated to be 26.2 kcal/mol. The polymerization system involved ESR‐observable propagating polymer radicals under the practical polymerization conditions. ESR‐determined rate constants of propagation (k_p) and termination (k_t) were k_p = 19 L/mol s and k_t = 5.8 × 10³ L/mol s at 110°C, respectively. The molecular weight of the resultant poly(DMVP)s was low (M_n = 3.4 ? 3.5 × 10³), because of the high chain transfer constant (C_m = 3.9 × 10^?2 at 110°C) to the monomer. DMVP (M₁) showed a considerably high reactivity in the radical copolymerization with trimethoxyvinylsilane (TMVS) (M₂) at 110°C in bulk, giving an inorganic component‐containing functional copolymer with potential flame‐retardant properties; r₁ = 1.6 and r₂ = 0. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermally induced homolytic scissions of interunitary bonds in a softwood lignin solution: A spin‐trapping study

Unstable chemical species, that is, radicals generated by the thermal treatment of a dimethyl sulfoxide (DMSO) solution of the lignin of a softwood, Yezo spruce (Picea jezoensis Carr.), were studied in detail with an electron spin resonance (ESR) method combined with a spin‐trapping technique. An unstable secondary carbon radical (～CH ·) in the solution was trapped as a stable nitroxide spin adduct [R? (N? O ·)? CH～ (R = tert‐butyl benzene)] when the DMSO solution was heat‐treated in the presence of a spin‐trapping reagent [2,4,6‐tri‐tert‐butylnitrosobenzene (BNB)] at about 40°C. This meant that alkyl phenyl ether bonds (～CH? O‐phenyl), known as interunitary lignin bonds, were homolytically scissioned by the thermal treatment in the lignin solution. A detailed analysis of the ESR spectrum revealed that three kinds of radicals—primary (～CH₂ ·), secondary (～CH ·), and tertiary (～C ·) carbon radicals—were trapped as stable spin adducts at about 60°C, although the phenoxy radical (Ph? O ·) was not trapped by the BNB spin trap as the counter radical of the secondary carbon radical. This suggested that a fairly large steric hindrance existed between the so‐called guaiacoxy radical with a methoxy group in the ortho position and the BNB molecule bearing two butyl groups as bulky moieties in the ortho positions. However, the phenoxy radicals in the lignin solution were stable up to about 60°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2136–2141, 2004