Excitation dynamics in α-sexithiophene single crystals and UHV-grown films

• Published in: Journal of luminescence 1998-02, Vol.76, p.416-419
• Main Authors: Hopmeier, M., Marks, R.N., Michel, R., Muccini, M., Murgia, M., Zamboni, R., Taliani, C., Horowitz, G., Garnier, F., Oestreich, M., Mahrt, R.F.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Oligothiophene; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Organic compounds and polymers; Organic compounds, polymers; Photoluminescence; Physics; Solid organic materials; Structural disorder; Time-resolved photoluminescence; Visible and ultraviolet spectra
• ISSN: 0022-2313; 1872-7883
• DOI: 10.1016/S0022-2313(97)00229-9

We have investigated the disorder-determined optical properties of α-sexithiophene by comparing measurements of an evaporated film and a single crystal. We observed for the first time sharp lines in absorption and photoluminescence from both samples representing the intrinsic electronic properties of the material. The time-integrated emission spectra of both samples are dominated by radiative trap emission, which is more pronounced in the film due to the higher degree of disorder. Photoluminescence excitation and site-selective photoluminescence measurements show the different origin and character of the traps in the samples. We attribute the single crystal traps to the so-called X-traps while the nature of the traps in the film is still undetermined. Time-resolved photoluminescence measurements of the film show a fast transfer process of the sharp bulk emitters to the unstructured trap emission within the first 50 ps after excitation. A comparable process is observable in the single crystal, showing a slower dynamics due to lower trap density.