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Selective Luminescence Spectroscopy of Poly(p-Phenylene) Thin Films at Room Temperature
Published online by Cambridge University Press: 10 February 2011
Abstract
Selectively excited room-temperature luminescence spectra are reported for thin films of poly(p-phenylene) (PPP) deposited onto quartz substrata. The spectra exhibit a localization threshold in the low-energy tail of the luminescence excitation band at vloc.= 22400 cm−1, 2200 cm−1 below the maximum of the excitation spectrum. Upon laser excitation at Vex < Vloc., the maximum Vem of the luminescence spectrum shifts linearly with Vex due to selective excitation of polymer segments. It was found that there exists the frequency range where the slope of the Vem vs Vex dependence is smaller than unity, which corresponds to our previous model calculations for the case of selective excitation of chromophores through broad phonon bands. At vex > vloc,, the luminescence spectrum is independent of Vex. This behavior can be explained if one assumes that upon excitation below the localization threshold the luminescence is related to polymer segments directly excited by laser, whereas upon exciting above the threshold the fast energy relaxation takes place from initially excited states to lower-lying states, from which uminescence occurs.
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- Copyright © Materials Research Society 1996