| Thin films of composites made by incorporation of silicon oxide (SiO2) or titanium oxide (TiO2) nanoparticles into poly[2-methoxy-5-(2'-ethylhexoxy-p-phenylene vinylene] (MEH-PPV) were deposited by spin-coating from p-xylene solutions and their optical properties were investigated. SEM images showed that different extents of aggregates were formed for two kinds of nanocomposites. The UV-vis absorption spectra of MEH-PPV/SiO2 and MEH-PPV/TiO2 films showed a small red shift (~ 5 nm) as compared with that of pristine polymer. However, the structure of MEH-PPV was not affected as revealed by infrared and Raman experiments. This result is different from that obtained in PPV/oxide nanocomposites in which, the conjugated length of PPV main chain was reduced. Similarly, a small red shift was found in PL emission spectra with increasing the content of oxide nanoparticles. The PL degradation experiments showed that blending with SiO2 nanoparticles could enhance the luminescent stability of MEH-PPV. By blending with 8% SiO2 nanoparticles of 20 nm diameter, the PL intensity of MEH-PPV film attained 46% of the original one, while it decreased to 20% for pristine MEH-PPV after four weeks of exposure to ambient air. The effect of TiO2 nanoparticles to stabilize MEH-PPV thin films is though less important than that of SiO2. |
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