Photophysical and Electroluminescence Characteristics of Polyfluorene Derivatives with Triphenylamine.

In this work, polymers of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-triphenylamine] with side chains containing: pyrene (C1), diphenyl (C2), naphthalene (C3), and isopropyl (C6) structures were synthesized via a Suzuki coupling reaction. The structures were verified using NMR and cyclic voltammetry measurements provide the HOMO and LUMO of the polymers. The polymer with pyrene (C1) and naphthalene (C3) produced photoluminescence in the green while the polymer with the side chain containing diphenyl (C2) and isopropyl (C6) produce dual emission peaks of blue-green photoluminescence (PL). In order to examine the electroluminescence properties of the polymers, the solutions were spin-coated onto patterned ITO anode, dried, and subsequently coated with an Al cathode layer to form pristine single layer polymer LEDs. The results are compared to a standard PFO sample. The electroluminescence spectra resemble the PL spectra for C1 and C3. The devices of C2, C3, and C6 exhibit voltage-dependent EL. An additional red emission peak was detected for C2 and C6, resulting in spectra with peaks at 435 nm, 490 nm, and 625 nm. The effects of the side chains on the spectral characteristics of the polymer are discussed.

Direct synthesis of nanodiamonds by femtosecond laser irradiation of ethanol.

Carbon nanomaterials exhibit novel characteristics including enhanced thermal, electrical, mechanical, and biological properties. Nanodiamonds; first discovered in meteorites are found to be biocompatible, non-toxic and have distinct optical properties. Here we show that nanodiamonds with the size of <5 nm are formed directly from ethanol via 1025 nm femtosecond laser irradiation. The absorption of laser energy by ethanol increased non-linearly above 100 µJ accompanied by a white light continuum arises from fs laser filamentation. At laser energy higher than 300 µJ, emission spectra of C, O and H in the plasma were detected, indicating the dissociation of C2H5OH. Nucleation of the carbon species in the confined plasma within the laser filaments leads to the formation of nanodiamonds. The energy dependence and the roles of the nonlinear phenomenon to the formation of homogeneous nanodiamonds are discussed. This work brings new possibility for bottom-up nanomaterials synthesis based on nano and ultrafast laser physics.

Low-temperature synthesis of indium tin oxide nanowires as the transparent electrodes for organic light emitting devices.

Low-temperature growth of indium tin oxide (ITO) nanowires (NWs) was obtained on catalyst-free amorphous glass substrates at 250 °C by Nd:YAG pulsed-laser deposition. These ITO NWs have branching morphology as grown in Ar ambient. As suggested by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), our ITO NWs have the tendency to grow vertically outward from the substrate surface, with the (400) plane parallel to the longitudinal axis of the nanowires. These NWs are low in electrical resistivity (1.6×10⁻4 Ω cm) and high in visible transmittance (~90­96%), and were tested as the electrode for organic light emitting devices (OLEDs). An enhanced current density of ~30 mA cm⁻² was detected at bias voltages of ~19­21 V with uniform and bright emission. We found that the Hall mobility of these NWs is 2.2­2.7 times higher than that of ITO film, which can be explained by the reduction of Coulomb scattering loss. These results suggested that ITO nanowires are promising for applications in optoelectronic devices including OLED, touch screen displays, and photovoltaic solar cells.