Electrical and optical properties of poly(2-dodecanoylsulfanyl-p-phenylenevnylene) and its application in electroluminescent devices

We describe the optical and electrical characterization of a poly(p-phenylenevinylene) derivative: poly(2-dodecanoylsulfanyl-p-phenylenevinylene) (12COS-PPV). The electrical characterization was carried out on devices with the FTO\PEDOT:PSS\12COS-PPV/Al structure. Positive charge carrier mobility mu(h) of similar to 1.0 x 10(-6) cm(2) V(-1) s(-1) and barrier height phi of similar to 0.1 eV for positive charge carrier injection at the PEDOT:PSS/12COS-PPV interface were obtained using a thermionic injection model. FTO\PEDOT:P55\12COS-PPV/Ca devices exhibited green-yellow electroluminescence with maximum emission at lambda = 540 nm.

All-optical switching device for infrared based on PbTe quantum dots

Multilayers of PbTe quantum dots embedded in SiO2 were fabricated by alternate use of Pulsed Laser Deposition (PLD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques. The morphological properties of the nanostructured material were studied by means of High Resolution Transmission Electron Microscopy (HRTEM), Grazing-Incidence Small-Angle X-ray scattering (GISAXS) and X-ray Reflectometry (XRR) techniques. A preliminary analysis of the GISAXS spectra provided information about the multilayer periodicity and its relationship to the size of the deposited PbTe nanoparticles. Finally multilayers were fabricated inside a Fabry-Perot cavity. The device was characterized by means of Scanning Electron Microscopy (SEM). Transmittance measurements show the device functionality in the infrared region. (C) 2007 Elsevier Ltd. All rights reserved.

Optical Properties and Charge-Transfer Excitations in Edge-Functionalized All-Graphene Nanojunctions

We investigate the optical properties of edge-fiinctionalized graphene nanosystems, focusing on the formation of junctions and charge-transfer excitons. We consider a class of graphene structures that combine the main electronic features of graphene with the wide tunability of large polycyclic aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we show that, upon convenient choice of functional groups, low-energy excitations with remarkable charge-transfer character and large oscillator strength are obtained. These properties can be further modulated through an appropriate width variation, thus spanning a wide range in the low-energy region of the UV-vis spectra. Our results are relevant in view of designing all-graphene optoelectronic nanodevices, which take advantage of the versatility of molecular functionalization, together with the stability and the electronic properties of graphene nanostructures.

Influence of different solvents on the structural, optical and morphological properties of CdS nanoparticles

CdS is one of the most important II-VI semiconductors, with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized via microwave-assisted solvothermal technique. Structural and morphological characterization revealed the presence of crystalline structures presenting single phase with different morphologies such as ""nanoflowers"" and nanoplates depending on the solvent used. Optical characterization was made by diffuse reflectance and photoluminescence spectroscopy, revealing the influence of the different solvents on the optical properties due to structural defects generated during synthesis. It is proposed that these defects are related to sulfur vacancies, with higher concentration of defects for the sample synthesized in ethylene glycol in comparison with the one synthesized in ethylene diamine. (C) 2011 Elsevier B.V. All rights reserved.

Thickness and Annealing Temperature Effects on the Optical Properties and Surface Morphology of Layer-by-Layer Poly(p-phenyline vinylene) plus Dodecylbenzenesulfonate Films

The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV)+dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 degrees C had a dichroic ratio delta = 2.3 and order parameter r = 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with delta = 1.0 for a 75-layer LbL PPV + DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the self-covariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 206-213, 2011

Development of impedimetric and optical calcium biosensor by using modified gold electrode with porcine S100A12 protein

We describe the development of a label free method to analyze the interactions between Ca(2+) and the porcine S100A12 protein immobilized on polyvinyl butyral (PVB). The modified gold electrodes were characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and surface plasmon resonance (SPR) techniques. SEM analyses of PVB and PVB-S100A12 showed a heterogeneous distribution of PVB spherules on gold surface. EIS and CV measurements have shown that redox probe reactions on the modified gold electrodes were partially blocked due the adsorption of PVB-S100A12, and confirm the existence of a positive response of the immobilized S100Al2 to the presence of calcium ions. The biosensor exhibited a wide linear response to Ca(2+) concentrations ranging from 12.5 to 200 mM. The PVB-S100A12 seems to be bound to the gold electrode surface by physical adsorption: we observed an increase of 1184.32 m degrees in the SPR angle after the adsorption of the protein on the PVB surface (in an indication that 9.84 ng of S100A12 are adsorbed per mm(2) of the Au-PVB electrode), followed by a further increase of 581.66 m degrees after attachment of the Ca(2+) ions. In addition, no SPR response is obtained for non-specific ions. These studies might be useful as a platform for the design of new reusable and sensitive biosensing devices that could find use in the clinical applications. (C) 2010 Elsevier B.V. All rights reserved.

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE(3+) = Eu(3+), Gd(3+) and Tb(3+)) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H(2)O)(2)], [RE(TLA)(H(2)O)(4)] and [RE(TMA)(H(2)O)(G)], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd(3+)-(BTC) complexes showed that the triplet states (T) of the BTC(3-) anions have energy higher than the main emitting states of the Eu(3+) ((5)D(0)) and Tb(3+) ((5)D(4)), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Omega(2)) of Eu(3+)-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited (5)D(0) and (5)D(4) levels of the Eu(3+) and Tb(3+) ions is discussed. The emission quantum efficiencies (eta) of the (5)D(0) emitting level of the Eu(3+) ion have been also determined. In the case of the Tb(3+) ion, the photoluminescence data show the high emission intensity of the characteristic transitions (5)D(4) -> (7)F(J) (J=0-6), indicating that the BTC ligands are good sensitizers. The RE(3+)-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials. (C) 2009 Elsevier B.V. All rights reserved.

Novel electroluminescent devices containing Eu(3+)-(2-acyl-1,3-indandionate) complexes with TPPO ligand

Fabrication and electroluminescent properties of devices containing europium complexes of general formula [Eu(ACIND)(3)(TPPO)(2)], where ACIND, 2-acyl-1,3-indandionate ligands: and TPPO, triphenylphosphine oxide. as emitter layers are discussed. The double-layer devices based on these complexes present the following configurations: device 1: ITO/TPD/[Eu(AlND)(3)(TPPO)(2)]/Al: device 2: ITO/TPD/[Eu(ISOV-IND)(3)(TPPO)(2)]/Al and device 3: ITO/TPD/[Eu(BIND)(3)(TPPO)(2)]/Al, where AlND, 2-acetyl-1,3-indandionate; ISOVIND, 2-isovaleryl-1,3-indandionate; and BIND, 2-benzoyl-1,3-indandionate, respectively. These devices exhibited photo and electroluminescent emissions. An important characteristic presented by devices is that their electroluminescent (EL) spectra, in the region of (5)D(0) -> (7)F(J) (J = 0, 1, 2, 3 and 4) transitions of Eu(3+) ion, show profiles that are different from photoluminescent (PL) ones. In addition to narrow bands arising from intraconfigurational-4f(6) transitions, devices 1 and 2 also exhibited a broad band with maximum at around 500 nm which is assigned to electrophosphorescence from the indandionate ligands. On the other hand, EL spectra of device 3 present only narrow bands from (5)D(0) -> (7)F(J) transitions. [Eu(ACIND)(3)(TPPO)(2)] complexes are promising candidates to prepare efficient organic light-emitting devices (OLEDs) when compared with those containing Eu(3+)-complexes of aliphatic beta-diketonate anions. (C) 2009 Elsevier B.V. All rights reserved.

Polymeric electro-mechanic devices applied to antibiotic-controlled release

Polymeric electroactive blends formed by electropolymerized aniline inside a non-conductive polyacrylamide porous matrix were already shown as suitable materials for the electrocontrolled release of model compounds like safranin. In this paper the intermolecular interactions between the two components of the blend are put in evidence by Raman spectroscopy measurements. Also, in situ optical microscopy was used to follow changes occurring in the polyaniline/polyacrylamide blend during pyrocathecol violet release tests. These two sets of experiments show the possibility of controlling electrochemically the release of both, safranin (a cation) and pyrocathecol violet (an anion) and allow to infer a release mechanism based on the electromechanical properties of the blends explaining the dependence of the release kinetics on the applied potential. Tetracycline release curves for different potentials and pHs are shown and the obtained profiles are in agreement with those expected for a device acting as an electrochemically driven pump due to the artificial muscle properties of the conducting phase of the blends. (c) 2007 Elsevier B.V. All rights reserved.

All solid-state electrochromic devices with gelatin-based electrolyte

6 x 8cm(2) electrochromic devices (ECDs) with the configuration K-glass/EC-layer/electrotype/ion-storage (IS) layer/K-glass, have been assembled using Nb2O5:Mo EC layers, a (CeO2)(0.81)-TiO2 IS-layer and a new gelatin electrolyte containing Li+ ions. The structure of the electrolyte is X-ray amorphous. Its ionic conductivity passed by a maximum of 1.5 x 10(-5) S/CM for a lithium concentration of 0.3g/15ml. The value increases with temperature and follows an Arrhenius law with an activation energy of 49.5 kJ/mol. All solid-state devices show a reversible gray coloration, a long-term stability of more than 25,000 switching cycles (+/- 2.0 V/90 s), a transmission change at 550 nm between 60% (bleached state) and 40% (colored state) corresponding to a change of the optical density (Delta OD = 0. 15) with a coloration efficiency increasing from 10cm(2)/C (initial cycle) to 23cm(2)/C (25,000th cycle). (c) 2007 Elsevier B.V. All rights reserved.