1,721,040 research outputs found
Solvation effects and inhomogeneous broadening in optical spectra of phenol blue
No full textElectronic and vibrational spectra of phenol blue dissolved in a few solvents are carefully analyzed on the basis of a simple theoretical model accounting for electron-molecular vibration coupling and for solvation. Nonresonant Raman and electronic absorption spectra measured in a series of solvents with similar refractive index and increasing dielectric constant are the basis to extract a reliable set of microscopic parameters. On the basis of these parameters, we reproduce the large and impressive inhomogeneous broadening effects observed in resonant Raman spectra collected in polar solvents. Solvation effects on the first hyperpolarizability are also discussed. © 2000 American Chemical Society
A new method for the determination of molecular diffusion coefficient in polymer films by simple UV-VIS spectroscopy
No full textThe possibility to evaluate molecular diffusion coefficient in polymer films directly in-situ is critical to assess barrier properties of packaging systems. Using the polymer packaging itself as smart sensor could lead to increase shelf-life, minimize wastes, and food poisoning effects. In this work we report on a new method that exploit simple UV-Vis spectroscopy to identify diffusion of small molecules in the vapor phase through both commercial polymer packaging systems and into polymer multilayered structures. The new method allows to determine molecular diffusion coefficient values in full agreement with gravimetric data reported in literature
Universal Design Rules for Flory–Huggins Polymer Photonic Vapor Sensors
No full textMultilayered photonic sensors that rely on polymer-solvent Flory-Huggins interactions are drawing increasing interest owing to their broad-band selectivity, even among mixtures, without the need for chemical targeting. Moreover, these sensors provide simple colorimetric responses, and easy, quick fabrication both on laboratory and industrial scales. However, complex optical responses and slow response times are limiting their development. In this work, the behavior of different photonic sensor architectures is analyzed to speed up response time and define a strategy to simplify their spectral behavior. To this end, the effect of interfaces, materials order, and thickness on the diffusion kinetics of a single reference analyte in the multilayered sensors is studied to design the optimal structure
Growth and optical studies of opal films as three-dimensional photonic crystals
No full textThree-dimensional artificial opals showing photonic crystals properties are grown by self-assembly of polystyrene nanospheres. Atomic force microscopy (AFM) images of opal surfaces show domains with regular triangular and squared packing of the spheres separated by cracks whose relative fraction depends on the sample quality. The energy position of an optical pseudo gap in transmittance spectra is observed by varying the angle of incidence and is accounted for by theoretical calculations of the photonic band structure based on a planewave
expansion method
Anisotropic photoluminescence properties of oriented poly(p-phenylene-vinylene) films: Effects of dispersion of optical constants
No full textWe report on the effects of dispersive optical constants on the anisotropic photoluminescence spectra of
highly oriented poly-phenylene-vinylene films. Polarized transmittance, reflectance, and photoluminescence
PL spectra have been measured over a broad spectral range, at different temperatures. Due to the high degree
of chain orientation in the polymer films, the emission properties are highly anisotropic. The PL spectral shape
and external quantum efficiency are significantly affected by self-absorption inside the polymer film and by
refractive effects at the polymer-air interface. In order to elucidate these aspects we have determined the
dispersion of the parallel and perpendicular components of the complex dielectric constant, by which
the PL spectra have been corrected according to Fresnel equations. After correction, the PL intensity is found
to be higher when the excitation is polarized perpendicular to the stretching direction, a fact that we attribute
to charge-induced PL quenching. We have also considered the influence of the refractive index on the PL
spontaneous emission rate and on the light extraction from the polymer film. The spectral dependence of the
emission anisotropy functions of the corrected PL spectra indicates the presence of two distinct emitting
species, which may originate from intramolecular and intermolecular states
Nature-inspired mechanochromic photonic crystals: advancements in distributed Bragg reflectors for strain sensing
No full textPolarized optical and photoluminescence properties of highly oriented poly(p-phenylene-vinylene)
No full textWe report on the anisotropic reflectance (R), transmitlatice (T) and photoluminescence (PL) properties of stretch-oriented free standing films of poly(phenylene-vinylene) (PPV) at different temperatures. The PL quantum efficiency is strongly dependenl on the pumo polarization, being higher when pump is polarized perpendicular lo the polymer chain orientation. Independently of the pump polarization, we find that the PL emission spectra are mainly polarized along the polymer chain direction. The PL spectra have been corrected both for the number of absorbed photons and for self-absorption of the emitted light.
Frank-Condon analysis of the oscillator strengrh for absorption and corrected emission spectra suggest that two different "chromophores" contribute to the optical properties
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