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 2.05 eV, implying a Stokes shift of 0.15eV. Studies of the temperature dependence (T more than or equal to 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
- ADA107831
Entities
People
- A. J. Heeger
- Alan G. Macdiarmid
- L. Lauchlan
- S. Etemad
- T. -c. Chung
Organizations
- University of Pennsylvania