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In this work we have studied the emissions from luminescent polymeric blends, aiming to obtain a white emission. Two of the materials, a polyfluorene derivative matrix poly(9,9-dihexyl-2,7-fluorene) (LaPPS 10, labeled as L10) and a polyvinylene-derivative guest (poly[(9,9-dihexyl-9H-fluorene-2,7-diyl)-1,2-ethenediyl-1,4-phenylene-1,2-ethenediyl] (LaPPS 16—L16), have not been extensively studied. The L10 was used as a matrix (host) and the L16 as a dopant (guest). A commercial polyvinylene (MDMO-PPV) was also used as a dopant. In order to achieve the white emission, it is necessary to control the energy transfer among the components of the blend. The emissions of solutions were analyzed, varying the concentration of the materials. From that, solutions of polymeric blends of L10:L16 (at different ratios) were spincoated, forming solid state films. The emission of these binary blend films were monitored as a function of the guest concentration. Therefore, in order to cover the red region of the visible spectrum, MDMO-PPV was added to the initial blend, forming a ternary blend (L10:L16:MDMO-PPV). The emissions of these blend films were studied, varying the concentration of the MDMO-PPV. Using the optimal results for the material ratios of these ternary blends, aiming for the white emission, electroluminescent devices were produced and the electroluminescence was studied. A whitish emission was obtained with the 97.5:0.5:2.0 blend, leading to the CIE coordinates 0.31:0.36.

This study analyzed the interfaces between poly(3-hexylthiophene) (P3HT) on an Au substrate (Au/P3HT) and on Au coated with poly(3,4-ethyldioxythiophene) doped with poly(4-styrenesulfonate) (Au/PEDOT:PSS/P3HT). The different morphologies on the nanostructured Au surface were obtained by applying cyclic potentials using cyclic voltammetry to produce different interfaces in the two systems studied. Under atomic force microscopy (AFM), the number of potential activation cycles was found to produce different roughnesses on the surfaces of the Au electrodes. The interfaces formed were examined by electrochemical impedance spectroscopy (EIS) to identify charge transfer processes for the different segments of the P3HT. The systems were characterized optically by measuring photoluminescence (PL), emission decay time and photoluminescence quantum yield (PLQY). It was observed that the differences in the surface morphologies of the substrates significantly influenced the electrical and optical properties of the P3HT at the interfaces.

A systematic study of luminescence from blends made of poly (9, 9-dioctylfluorene-2, 7-diyl) (PFO) and poly (3-octylthiophene-2, 5-diyl) (P3OT), and its photophysics was carried out. Acceptor concentration influence and sample preparation conditions was analyzed, particularly regarding the solvent, in order to control emission through the entire visible spectrum, and to understand the physical processes involved. An additional emission band observed in PFO:P3OT films with low concentration of P3OT was studied through confocal luminescence microscopy and was attributed to a decrease of energy transfer between P3OT molecules leading to an emission through chains with smaller conjugation length. The extra emission was also separated from the others by Time Resolved Emission Spectroscopy due to the fact that its lifetime is longer than those of the other emissions. Balance control of the emission through PFO (blue), low conjugation chains of P3OT (green) and P3OT aggregates (red) was possible changing the solvent and the way to prepare samples, that causes a greater or lesser amount of β phase in PFO. The study of the energy processes involved was also performed.

The optical properties of electrochemically synthesized P3HT films were studied. After the synthesis, the samples were divided into two groups: as prepared (P3HT-E) and the chemically reduced (dedoped) in a basic medium (P3HT-D). These films were characterized by photoluminescence (PL), Raman and photoluminescence time decay techniques. Comparing the PL spectra of the films, it is noted that P3HT-D has a higher PL intensity. The films were exposed to a continuously incident 405 laser and the PL spectra were monitored every 10 min. For both samples, the photoluminescence intensity along the photo-irradiation showed an increase, although the P3HT-E sample presented a greater increase. Regarding the Raman spectra before and after the photo-irradiation, it was noticed that for P3HT-D there were no changes, whereas P3HT-E showed significant changes. The Raman spectrum of P3HT-E sample at the photo-irradiated point was very similar to the Raman spectrum of P3HT-D. Thus, it was proposed that laser irradiation induces a reduction process similar to chemical reduction. Although both processes lead to an increase in the PL intensity, there is a difference in the position of the emission bands. Unlike chemical doping, the photoreduction does not remove the charge transfer complexes of the polymer matrix, but only breaks their bond with the backbone chain. From the data of PL decay, it was observed that in the film P3HT-E, there was a predominance of longer times, evidencing the presence of barriers for the energy transfer, while, for the P3HT-D, the contribution of shorter decay times predominates, evidencing a greater energy transfer between the chains.

In this work, poly(3-hexylthiophene) (P3HT) film was synthesized electrochemically in non-aqueous media through the oxidation of the 3-hexylthiophene monomer using a standard three-electrode cell in acetonitrile with 0.100 mol L−1 LiClO4. The polymeric thick film was deposited on platinum plates for best quality control of the process. Cyclic voltammetry of this material showed two bands of oxidation and two bands of reduction attributed to radical cation and dication segments in the polymer chain. These were characterized by reflectance and Raman spectra, of the reduced (chemically de-doped) and oxidized (electrochemically doped) films. The generated film was subjected to anodic potentials of 1.00 and 1.45 V and characterized by an in situ Raman technique, which indicated the stabilization of the radical cation segments. In addition Raman ex situ spectra of as-prepared film was obtained. The increase in the irradiation time of the sample was enough to alter the nature of the constituent species of the oxidized film, preferably favoring the aromatic chains, together with the dication segments. Photoluminescence spectra showed a larger contribution of dication than radical cation segments for the chemically de-doped sample and under this condition showed good stability, even with variation in laser power. SEM images of P3HT film with indication of the thickness and spherical shape of the sample studied were obtained. Aided by these data it was possible to verify the Stokes shift and ionization potential (I p), electron affinity (E.A.) and energy gap (E g) parameters.

AlxGa1-xAs/GaAs double quantum well structures with different well thickness and different barrier aluminum concentration (x = 0.17, 0.30, 0.40) were characterized by the photoluminescence technique. The temperature dependence of excitonic transitions in the temperature range of 2 K to 300 K were investigated. The photoluminescence data obtained give clear evidence of the influence of the aluminum concentration on the temperature dependence of excitonic transitions in the quantum wells. Varshni [Physica (Utrecht) 34, 194 (1967)], Vi na et al. [Phys. Rev. B 30, 1979 (1984)] and Passler [Phys. Stat. Sol. (b) 200, 155 (1997)] models were used to fit the experimental points.