Accession Number : ADA107888


Title :   Photoexcitations in Polyacetylene.


Descriptive Note : Technical rept.,


Corporate Author : PENNSYLVANIA UNIV PHILADELPHIA DEPT OF PHYSICS


Personal Author(s) : Lauchlan,L ; Etemad,S ; Chung,T C ; Heeger,H J ; MacDiarmid,Alan G


Full Text : http://www.dtic.mil/get-tr-doc/pdf?AD=ADA107888


Report Date : 11 Nov 1981


Pagination or Media Count : 47


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)


Descriptors :   *POLYMERS , *PHOTOLUMINESCENCE , *ACETYLENE , *PHOTOCONDUCTIVITY , TEMPERATURE , PHOTOCHEMICAL REACTIONS , EXCITATION , RAMAN SPECTROSCOPY , CHARGE CARRIERS , QUENCHING , TRANSPORT PROPERTIES , RECOMBINATION REACTIONS , ABSORPTION , STOKES RADIATION , BAND SPECTRA , ISOMERIZATION , ACTIVATION ENERGY


Subject Categories : Radiation and Nuclear Chemistry
      Polymer Chemistry
      Atomic and Molecular Physics and Spectroscopy


Distribution Statement : APPROVED FOR PUBLIC RELEASE