Spectral,luminescent, and lasing properties of pyran derivatives in thin acrylic films under optical excitation

Absorption and fluorescence spectra and lasing ability of pyran derivatives in thin polymeric layers (0.5–0.8 μm) based on polymethylmethacrylate and copolymerized methylmethacrylate and methacrylic acid are investigated. It is revealed that the absorption and luminescence intensities and the laser service lifetime of dicyanomethilene (DCM) pyran derivatives are determined by their composition and nature of the polymeric medium. Compositions based on DCM and examined polymers are of interest for preparation of thin-film active media lasing in the red range of the spectrum. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 63–66, October, 2005.     

Solvent-free double-layer capacitors with polymer electrolytes based on 1-ethyl-3-methyl- imidazolium triflate ionic liquid

A series of electrochemical capacitors based on carbon powders (specific surface areas 830 and 2600 m²/g) and polymer electrolytes were constructed and tested. Both polymer electrolytes as well as capacitor electrodes, in the form of thin foils, were prepared by a casting technique. All-plastic capacitors were coin-shaped, with a diameter of 12–18 mm and a mass of ∼100–500 mg, and were constructed by sandwiching the polymer electrolyte between two electrodes. An ionic liquid, 1-ethyl-3-methyl-imidazolium triflate, served both as a source of ions as well as a polymer plasticiser. In some cases, sulpholane was added to the system as an additional plasticiser. Poly(acrylonitrile), poly(vinylidenefluoride), and its copolymer with hexafluoropropylene, poly(ethylene oxide), poly(vinyl alcohol) as well as poly(methylmethacrylate) served as a polymer matrix. Polymer electrolytes showed conductivity up to 16 mS/cm. The performance of the capacitors was determined by cyclic voltammetry, impedance spectroscopy and galvanostatic charging/discharging. Specific capacity was up to 230 F/g, expressed versus the mass of the carbon material. PACS 82.47.Uv     

Lasing efficiency of dyes incorporated into a nanoporous glass-polymer composite

We have used microsecond coherent pumping to study the lasing efficiency of active elements based on a nanoporous glass-polymer composite activated by organic dyes, as a function of the spectral composition of the pump within the main absorption band of the dye. We have shown that under the indicated excitation conditions, the lasing efficiency can exceed 40% and can be comparable with the lasing of liquid elements. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 708–716, September–October, 2008.     

Electrical and optical properties of pure and KClO3-doped P(MMA-CO-4VPNO) polymer electrolyte films

Ion-conducting polymer electrolyte films based on a copolymer poly(methyl-methacrylate-co-4-vinyl pyridine N-oxide) [P(MMA-CO-4VPNO)] complexed with potassium chlorate (KClO₃) were prepared by solution cast technique. The complexation of KClO₃ salt with the polymer was confirmed by X-ray diffraction and infrared studies. The electrical conductivity and optical absorption of pure and KClO₃-doped P(MMA-CO-4VPNO) polymer electrolyte films have been studied. The electrical conductivity increased with increasing dopant concentration, which is attributed to the formation of charge transfer complexes. The variation of electrical conductivity with temperature shows two regions with two activation energies. Optical properties like direct band gap, indirect band gap, and optical absorption edge were investigated for pure and doped polymer films in the wavelength range 300–550 nm. It was found that the energy gaps and band edge values shifted to lower energies on doping. The behavior is in an agreement with the activation energies obtained from the conductivity data.     

Distributed feedback dye laser holographically induced in improved organic–inorganic photocurable nanocomposites

Distributed feedback (DFB) lasing in permanent volume transmission gratings formed in a laser dye-doped organic–inorganic nanocomposite has been investigated. DFB laser cavities were fabricated using one-step two-beam holographic exposure of Pyrromethene 567 (PM567) doped photopolymerizable acrylate monomers containing inorganic (LaPO₄) nanoparticles. Compared to the formulation previously utilized, the material composition presented provides longer lifetime of the laser. Spectral and polarization properties, input–output and stability characteristics of the laser output have been investigated by varying the material composition and the patterning parameters. DFB lasing emission of the second and the third diffraction orders has been demonstrated. The spectral linewidth of ∼0.08 nm has been observed at a pump energy threshold of about 0.2 μJ/pulse for the second-order DFB lasing when pumped with 532 nm 500 ps laser pulses. Spectral tuning of the lasing output over ∼56 and ∼7 nm was obtained by varying the grating period and the content of inorganic nanoparticles in the polymer matrix, respectively.     

Linear and nonlinear optical properties of two-photon absorption dye doped linear copolymer

2-hydroxyethyl methacrylate (abbreviated as HEMA) and acrylonitrile have been used as the monomers to form a trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HMASPS) doped linear copolymer. The spectra of one and two-photon excited fluorescence and two-photon pumped superradiance and two-photon pumped lasing of the polymer all shifted to short wavelengths compared with the solution sample of the dye. The copolymer shows much longer one- and two-photon excited fluorescence lifetimes of nanoseconds. When pumped by the picosecond Nd:YAG laser, the superradiance and lasing can be simultaneously obtained. The maximum two-photon pumped lasing conversion efficiency is 3.3%. The place of the maximum upconversion efficiency of the copolymer does not coincide with that of the maximum nonlinear absorption.     

MAPLE-deposited polymer films for improved organic device performance

Matrix-assisted pulsed-laser evaporation (MAPLE) provides a mechanism for layer-by-layer growth to control the polymer–dielectric interface in organic metal–insulator–semiconductor (MIS) diodes and field-effect transistors (FETs). MAPLE-deposited copolymers of polyfluorene (PF) and polythiophene maintain their structural and optical properties, as determined by Raman spectroscopy, absorption, and photoluminescence. These films are further utilized in MIS and FET structures with SiO₂ and other polymer dielectrics. Since common polymer dielectrics prevent spin coating of solution processable polymers due to solubility effects, MAPLE is one of the only deposition techniques for investigating all polymer semiconductor-insulator interfaces. In this paper we present optical and electrical studies of MAPLE-deposited PF and polythiophene films in FETs and MIS structures. The FET carrier mobilities of these devices compare well with spin-coated devices. Capacitance–voltage and conductance–voltage from MIS structures with MAPLE-deposited PF copolymer films yield interface trap densities in the low 10¹² eV⁻¹ cm⁻² range.     

Spectroscopic characteristics of erbiumand ytterbium-activated laser media

Judd–Ofelt parameters (Ω₂ = 5.09∙10^–20, Ω₄ = 0.92∙10^–20, and Ω₆ = 0.63∙10^–20 cm²) and oscillator strengths of fundamental optical transitions involved in lasing at wavelength 1.54 μm have been calculated for borosilicophosphate glass co-activated with Er³⁺ and Tb³⁺ ions based on experimental luminescence and absorption spectra and refractive indices. The results were used to determine the emission (6∙10^–23 cm²) and absorption (5∙10^–21 cm²) cross sections for λ = 1.54 μm and the gain cross section as a function of inverse population levels.     

Fluorescence spectroscopy of potential electroluminescent materials: Substituent effects on DSB and segmented PPV derivatives

The absorption and fluorescence of substituted distyrylbenzene (DSB) derivatives and segmented poly(phenylene vinylene) (PPV) derivatives are characterized by long-wavelength absorption maxima and absorption coefficients of λ_a = 380–450 nm, ε = 20,000–60,000 M⁻¹ cm¹ and fluorescence maxima, quantum yields, and decay times of λ_r = 440–530 nm, Φ_f = 0.2–0.9, and Τ = 0.8–2.5 ns, respectively. Alkoxy substituents at the central phenylene ring of DSB groups increase the bathochromic shift in the spectra in comparison to DSB, without a significant decrease in the high DSB fluorescence quantum yield. Both phenyl and cyano substitutions at the vinylene bridge lead to a further bathochromic shift of the fluorescence and a decrease in the quantum yield to ca. 0.4. The DSB derivatives and the related segmented PPV derivatives show nearly the same absorption spectra, fluorescence spectra, and radiative rate constantsk _f= Φ_f/Τ, indicating the efficacy of the segmentation of the polymer chain. The radiative rate constants determined by the Φ_f and Τ values and by the Strickler/Berg formula are in reasonable agreement. This supports the possibility of interpreting the properties of the polymers in terms of their DSB units. The decrease in the emission anisotropy can be ascribed to multistep energy transfer processes between different oriented segments.     

Poly(methylmethacrylate) as immobilization matrix for europium β-diketonates—Morphology and fluorescent properties

The properties of composites prepared by the immobilization of Eu(III) complexes with dibenzoylmethane and thenoyltrifluoracetone in poly(methylmethacrylate) are studied. The matrices are produced by polymerization of the monomer or by using chloroform solution of the polymer. The films produced from polymerized monomer by dip-coating or spray-pyrolysis are dense and uniform and show a tendency to form a chain structure. Uniform films, with separate sharp “peaks” or pores, 20-80 nm in diameter and grains with order size of 20 nm are formed from poly(methylmethacrylate) chloroform solution. The morphology depends on the nature of ligands and co-ligands, the matrix production method and the deposition method. Embedding of the complexes does not significantly influence the emission spectra of the produced films and membranes.     

Synthesis of the poly(N-isopropylacrylamides) containing tetraarylporphyrin substituents

In a brief form, the authors provide their developed methods of synthesis and modification of the poly(N-isopropylacrylamide) derivatives containing meso-tetraarylporphyrin substituents in the side chain. The specific features of absorption spectra of the compounds obtained and their dependence on the method of introduction of porphyrin groups into the polymer are discussed. The physical and chemical characteristics of the polymers described are given. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 538–541, July–August, 1999.     

Measurement of the thickness of thin polymer layers by infrared frustrated total internal reflection spectroscopy

A method is proposed for determining the thickness of thin (0.1–5.0 μm) polymer layers and coatings by means of infrared frustrated total internal reflection (FTIR) spectroscopy. This method is based on an analytic expression derived for the dependence of the intensities of absorption bands in IR FTIR spectra on the thickness of a polymer layer. The method is tested on model samples consisting of a thick film of polyethylene terephthalate with a layer of different thicknesses of polystyrene deposited on it. The advantage of this method is the ability to determine the thickness of thin polymer layers deposited on bulk or opaque polymer substrates. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 881–885, November–December, 2008.     

Enantiomeric PLA–PEG block copolymers and their stereocomplex micelles used as rifampin delivery

A novelty approach to self-assembling stereocomplex micelles by enantiomeric PLA–PEG block copolymers as a drug delivery carrier was described. The particles were encapsulated by enantiomeric PLA–PEG stereocomplex to form nanoscale micelles different from the microspheres or the single micelles by PLLA or PDLA in the reported literatures. First, the block copolymers of enantiomeric poly(l-lactide)–poly(ethylene–glycol) (PLLA–PEG) and poly(D-lactide)–poly(ethylene–glycol) (PDLA–PEG) were synthesized by the ring-opening polymerization of l-lactide and d-lactide in the presence of monomethoxy PEG, respectively. Second, the stereocomplex block copolymer micelles were obtained by the self-assembly of the equimolar mixtures of enantiomeric PLA–PEG copolymers in water. These micelles possessed partially the crystallized hydrophobic cores with the critical micelle concentrations (cmc) in the range of 0.8–4.8 mg/l and the mean hydrodynamic diameters ranging from 40 to 120 nm. The micelle sizes and cmc values obviously depended on the hydrophobic block PLA content in the copolymer. Compared with the single PLLA–PEG or PDLA–PEG micelles, the cmc values of the stereocomplex micelles became lower and the sizes of the stereocomplex micelles formed smaller. And lastly, the stereocomplex micelles encapsulated with rifampin were tested for the controlled release application. The rifampin loading capacity and encapsulation efficiency by the stereocomplex micelles were higher than those by the single polymer micelles, respectively. The drug release time in vitro was depending on the composites of the block copolymers and also could be controlled by the polymer molecular weight and the morphology of the polymer micelles.     

Rheological properties and impedance spectroscopy of PMMA-PVdF blend and PMMA gel polymer electrolytes for advanced lithium batteries

In the present study, blend ionic conducting membranes formed by poly(methylmethacrylate (PMMA) / poly(vinilydenefluoride) (PVDF) (blend ratio PMMA/PVdF=80/20), lithium perchlorate (LiClO₄) as a salt and a mixture of ethylene carbonate (EC)-propylene carbonate (PC) as plasticizer are prepared and characterized by impedance spectroscopy and dynamic rheological experiments. We compared the results obtained on the blends with those on PMMA gel-based polymer electrolytes incorporating the same EC/PC mixture of plasticizer and the same quantities of salt. The main focus of this study is to illustrate the rheological data of the gels and blends electrolytes to point up their mechanical stability with the temperature in sight of the technological application. The conductivity values are reported in the 20–100 °C temperature range for different lithium salt contents, while the rheological behaviour has been recorded up to 140 °C. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Absorption by CS<Subscript>2</Subscript> molecules on “hot” band emission lines from a TEA CO<Subscript>2</Subscript> laser

We have measured absorption of emission from a TEA CO₂ laser, lasing on hot band lines, in pure CS₂ and a mixture of CS₂ with air, and we have determined the optimal lines for optical excitation. Numerical modeling has shown that as the peak intensity of the pump radiation is increased, we observe absorption saturation, the extent of which decreases as the pressure increases. The major factor responsible for absorption saturation is the “rotational bottleneck” effect. Depending on the peak intensity of the radiation, addition of a buffer gas can lead to an increase or decrease in the absorption. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 61–66, January–February, 2007.     

Dielectric and conductivity relaxations in PVAc based polymer electrolytes

The polymer electrolytes composed of a blend of poly (vinyl acetate) (PVAc) and poly (methylmethacrylate) (PMMA) as a host polymer and LiClO₄ as a salt are prepared by a solution casting technique. The formation of blend polymer- salt complex has been confirmed by FT-IR spectral studies. The conductivity- temperature plots are found to follow an Arrhenius nature. Arrhenius plot shows the decrease in activation energy with the increase in salt concentration. The dielectric behaviour of the sample is analysed using dielectric permittivity (ε′), dielectric loss (ε″) and electric modulus (M″) of the samples. The impedance cole- cole plot shows the high frequency semi- circle is due to the bulk effect of the material and the depression in the semicircle shows the non-Debye nature of the material. The bulk conductivity is found to vary between 2.5×10⁻⁵ Scm⁻¹ to 1.7×10⁻³ Scm⁻¹ with the increase of salt concentration of blend polymer samples. The migration energy derived from the dissipation factor is almost equal to the activation energy calculated from conductivity. The modulus spectrum of the samples shows the non-Debye behaviour of the polymer electrolyte films. The low frequency dispersion of the dielectric constant implies the space charge effects arising from the electrodes. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Modeling the cw lasing regime for diode-pumped solid state lasers

In terms of a system of balance equations, we propose a model for describing the operation of lasers based on solid-state quasi-three-level active media in the cw lasing regime with longitudinal pumping by emission from diode lasers, taking into account the spatial distribution of the pump and lasing light beams. We model the operation of lasers based on the active crystals Yb³⁺:NaLa(MoO₄)₂ and Yb³⁺:YVO₄, taking into account the proposed spatial distribution function of the intensity and the emission spectrum of the pump. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 55–60, January–February, 2007.     

Determination of the diffusion coefficients of dyes in polymer media by the absorption method with a high spatial resolution

The coefficients of diffusion of coumarin 7 in polyurethaneacrylate are determined by a new optical absorption method based on measurement of the absorption gradient at the boundary between the colored and colorless sections of the polymer. The dependence of the diffusion coefficient on concentration is found. The obtained values for the diffusion coefficients of the dye in an elastic matrix allow one to consider that the gradient optical elements in elastomers will be characterized by a relatively large lifetime. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 457–460, July–August, 2000.     

Electrical,optical, and structural characterization of polymer blend (PVC/PMMA) electrolyte films

Ion-conducting solid polymer blend electrolytes based on polyvinyl chloride (PVC)/poly methyl methacrylate (PMMA) complexed with sodium perchlorate (NaClO₄) were prepared in various concentrations by solution cast technique. The features of complexation of the electrolytes were studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. DC conductivity of the films was measured in the temperature range 303–398 K. Transference number measurements were carried out to investigate the nature of charge transport in the polymer blend electrolyte system. The electrical conductivity increased with increasing dopant concentration, which is attributed to the formation of charge transfer complexes. The polymer complexes exhibited Arrhenius type dependence of conductivity with temperature. In the temperature range studied, two regions with different activation energies were observed. Transference number data showed that the charge transport in this system is predominantly due to ions. Optical properties like absorption edge, direct band gap, and indirect band gap were estimated for pure and doped films from their optical absorption spectra in the wavelength region 200–600 nm. It was found that the energy gap and band edge values shifted to lower energies on doping with NaClO₄ salt. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamil Nadu, India, Dec. 7–9, 2006.     

Optimization of PDMS network for a fast response and sensitive actuation material applied in a MEMS spatial light modulator

The cross-linked networks of linear vinyl-terminated poly(dimethylsiloxane) (PDMS) with trimethylsiloxy-terminated methyhydrosiloxane–dimethylsiloxane copolymer (cross-linker) were investigated by tuning the cross-linker concentration, the chain length of linear PDMS and the functionality of the cross-linker. Response time and elastic modulus of the cross-linked PDMS elastomer were characterized by home-made measurement systems and analyzed based on their network topologies. An optimized PDMS elastomer, which has response time of 9 μs and elastic modulus of 601 kPa, was utilized as the actuation material in a MEMS spatial light modulator (SLM). The fabrication processes were described. This polymer based SLM has shown fast response time (9 μs) and successfully diffracted light into higher orders with 84% first-order diffraction efficiency.