The electroluminescence and photoluminescence characteristics of films of poly(phenylene vinylene)/gel-glass interpenetrating networks

Abstract

A series of poly(phenylene vinylene) (PPV)/gel-glass composites were prepared from mixtures of PPV precursor and silicon alkoxide methanol solution by employing a sol-gel process. The PPV/gel-glass composite, which is an interpenetrating network (IPN) structure, is used as the emissive layer in a polymeric light-emitting diode (LED). The addition of a small quantity of titanium ethoxide catalysed the reaction of gel-glass formation, making the PPV/gel-glass formation successful without phase separation and the luminescence of the composite film tunable. The luminescence characteristics of these PPV/gel-glass composites are dependent on the raw-material composition of silicon alkoxide and the molar ratio of PPV to gel-glass. From the ultra-violet/visible absorption spectrum, the conjugated length of these PPV/gel-glass composites can be seen to be shorter than that of pure PPV. The resultant PPV/gel-glasses emit light over a wide range from yellow-green (550 nm) to blue (484 nm) in the photoluminescence spectrum. Electroluminescent devices made from PPV/gel-glass 4 composites in the molar ratios of 1/1.17 and 1/2.33 shows a maximum emission peak at 515 and 510 nm, respectively. These PPV/gel-glass 4 LEDs showed a higher relative electroluminescence efficiency and a longer lifetime than pure PPV. The improvement in the device stability is related to the reduction of the thermal vibration of PPV chains during operation and the hindrance of carrier mobility in the IPN structure. Copyright (C) 1996 Elsevier Science Ltd.