Date of Award
Doctor of Philosophy
Physics and Astronomy
Photoluminescence (PL), optically detected magnetic resonance (ODMR), and nonresonant magnetic field effects (NFE) have been studied in polythiophene (PT) and poly(3-alkylthiophene) (P3AT). The PT samples studied were chemically coupled PT (c-PT) and electrochemically coupled PT (e-PT); the P3AT samples were poly(3-hexylthiophene) (HPT) and a copolymer of 3-benzylthiophene and 3-hexylthiophene (BHPT);The PL spectra of PT and P3AT exhibit a broad band centered between 1.6-1.9 eV, a narrow peak at 1.8-1.95 eV, and 0.18 eV phonon replicas of the narrow peak. The PL spectrum of e-PT is similar to the published spectra, while the PL of c-PT is dominated by a broad band centered near 1.6-1.7 eV, in contrast to previously published results. HPT and BHPT show almost identical PL spectra. In all samples, the integrated PL intensity is nearly temperature independent;ODMR was measured at X-band from 5 to 300K. Strong PL-enhancing signals ([delta]L/L ~eq 2 x 10[superscript]-3 at low temperatures) were detected at g = 2.003. The strength of the signal and its temperature dependence suggest that the ODMR probes unthermalized spins. In c-PT, the ODMR originates from a broad structureless PL band which is devoid of the phonon sidebands and is centered near 1.65 eV. The ODMR in each sample is composed of two components separated by [delta]g ~eq 6 x 10[superscript]-4. Although these two components are tentatively assigned to recombining positive and negative polarons, the possibility of two distinct long lived recombination mechanisms cannot be excluded. The ODMR signal decreases with increasing modulation frequency. The cutoff frequencies indicate that in addition to the well known fast PL, long PL lifetimes (10[superscript]-5 to 10[superscript]-3 sec) are present in these samples. The PL in P3AT appears to contain the longest lived component;Magnetic fields from 0 to 700 G cause broad enhancing and quenching changes in the PL intensity. The NFE in c-PT shows sharp peaks at 110 and 220 G. P3AT also shows a peak structure at 310 G. We tentatively attribute the peaks in c-PT to level crossings that occur when electron or hole Zeeman energies are resonant with the quadrupole splittings of iodine nuclei bound to the end of chains. (Abstract shortened with permission of author.) ftn*DOE Report IS-T-1375. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Bret Clark Hess
Hess, Bret Clark, "Spin polarization effects in the photoluminescence of polythiophene " (1988). Retrospective Theses and Dissertations. 9351.