Color changes in photoluminescence by doped, unconverted and partially converted poly( p -phenylene vinylene)

Although green-light-emitting devices based on poly(p-phenylene vinylene) ppv, have been made and reported by several researchers, it is also of interest to design light emitting devices which emit light in various parts of the visible spectrum, particularly in the blue region. In this letter the effect of doping and conversion time on the photoluminescence (PL) of pvv are investigated. It is observed that treating ppv films with sulfuric acid shifts the PL peaks to the blue region, and Li doping red-shifts the spectra. Unconverted and partially converted ppv films, on the other hand, show PL peaks at about 470 to 480 nm in the dark blue range. The shift in PL peak from green to blue is expected to be due to the decrease in conjugation length which determines the size of the band gap.