Impact of Erbium-Doped Silicon Nanocrystals on the Properties of Polyphenylene Vinylene Films
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IMPACT OF ERBIUM-DOPED SILICON NANOCRYSTALS ON THE PROPERTIES OF POLYPHENYLENE VINYLENE FILMS
Jeffery L. Coffer* and Junmin Ji Department of Chemistry Texas Christian University, Ft. Worth, Texas 76129*
Abstract This work describes our initial studies of Er-doped Si nanocrystal/poly(phenylene vinylene) (PPV) composites. Preliminary results have focused on the characterization of these materials via atomic force microscopy (AFM), profilometry, absorption/fluorescence spectroscopies, and current-voltage measurements. A particular point of emphasis here concerns the influence of the Er-doped Si nanocrystals on PPV photoluminescence and carrier transport.
Introduction Interfacial phenomena play a key role in the fundamental and technologicallyrelevant properties of luminescent organic semiconductors such as polyphenylene vinylene (PPV) 1 and its related derivatives. In principle, it should be possible to alter the structural, electronic, and photophysical interactions of these films with the incorporation of three dimensionally-confined semiconductor nanocrystals into the polymer matrix. The presence of both entities also permits the desired measurement(s) of carrier transport from an external medium to the nanocrystals. Thus we report here studies of Er-doped Si nanocrystal2/poly(phenylene vinylene) (PPV) composites. Studies of the fundamental properties of three dimensionally-confined Si nanoparticles and related materials have important ramifications for the future fabrication of ultra-small Si quantum dot devices relying on either carrier or photon transport for their function. As an optically-active dopant in silicon, erbium is of particular interest because of the coincidental match of its 1540 nm fluorescence in the near IR with the transmission maximum of SiO2. For these hybrid nanocrystal/polymer materials, preliminary results have focused on the characterization of these materials via atomic force microscopy (AFM), profilometry, absorption/fluorescence spectroscopies, and current-voltage measurements. The studies reported here focus on (1) the influence of Er-doped Si nanoparticles on the steady-state photoluminescence of the PPV and (2) the current-voltage behavior of light emitting diodes fabricated from these materials. *e-mail: [email protected]
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2 Experimental In order to fabricate PPV films doped with the Er-Si nanocrystals, a slight modification of the standard three-step synthetic route was used.3 Solutions of Er:Si nanocrystals of a mean diameter of 5.9 nm4 and the poly-electrolyte PPV precursor (poly{p-phenylene[1(tetrahydrothiophen-1-io)ethylene chloride]} were prepared by mixing Er:Si nanocrystals in ethylene glycol and PPV-precursor in methanol in selected ratios ranging from 8% Si to 23 % Si (w/w, based on the ratio of the mass of Si nanocrystals to the mass of the pre-polymer). This Er:Si/PPV-precursor solution then can be cast onto ITO-coated glass (or other substrate) to form a thin film. Subsequent heating of the film in high vacuum at ~220°C leads to the final nanocrystal-doped
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