Photoexcitations in Polyacetylene.
Abstract
The results of experimental studies of photoluminescence and photoconductivity in cis- and trans-(CH)x are presented. For cis-(CH)x, we find recombination luminescence in the scattered light spectrum at 1.9eV, near the interband absorption edge. The luminescence turns on sharply for excitation energies greater than 2.05eV, implying a Stokes shift of 0.15eV. Studies of the temperature dependence (T > or = 7K) show no loss of luminescence intensity even at temperatures as high as 300K. Isomerization of the same sample quenches the luminescence; we find no indication of luminescence near the interband absorption edge of trans-(CH)x even at temperatures as low as 7K. These results are discussed in the context of parallel phototransport studies. The quenching of the luminescence upon cis-trans isomerization is concurrent with the appearance of a large photoconductive response. The photoconductivity in trans-(CH)x has a threshold at 1.0eV, well below the interband absorption edge at 1.5eV, implying the presence of states deep inside the gap. The observation of luminescence in cis(CH)x, but not in trans-(CH)x; and the observation of photoconductivity in trans-(CH)x, but not in cis-(CH)x provide confirmation of the proposal that solitons are the photogenerated carriers. In trans-(CH)x, the degenerate ground state leads to free soliton excitations, absence of band edge luminescence, and photoconductivity. In cis-(CH)x the non-degenerate ground state leads to confinement of the photogenerated carriers, absence of photoconductivity, and to the observed recombination luminescence. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 11, 1981
- Accession Number
- ADA107888
Entities
People
- Alan G. Macdiarmid
- H. J. Heeger
- L. Lauchlan
- S. Etemad
- TC Mike Chung
Organizations
- University of Pennsylvania