True photoluminescence spectra revealed in electrospun light-emitting single nanofibers

We demonstrate for the first time that re-absorption and scatterings of photoluminescence (PL) significantly occurs among electrospun light-emitting nanofibers. Electrospun nanofibers composed of a blend of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] and poly(ethylene oxide) with and without LiCF_3SO_3 were prepared in controlled numbers. Different numbers of fibers showed different PL spectra even though the PL spectra from individual fibers were almost the same. Results of simulated PL spectra using UV-vis absorption spectra measured with and without an integrating sphere revealed that the change of PL spectral is due to re-absorption and scatterings of PL among the fibers. Although most PL spectra of electrospun nanofibers have been performed with a sheet or mat of many electrospun fibers, our study clearly shows that measuring PL spectrum of a single fiber is indispensable for precisely evaluating the aggregation states and the electronic states of conjugated polymers inside the fibers