|Time-resolved spectroscopy of excitonic states in metal-oxide nanostructures, conjugated polymers, and organic molecular crystals |
Institute for Advanced Materials and Devices
|Hikmat Najafov, Physics Dept., Lehigh University|
11:00 AM, CCR 201
Time resolved spectroscopy of exciton emission is known to be a powerful analytical tool for the studies of electron-phonon coupling, phonon termination of the luminescence, as well as the free carriers generation associated with exciton dissociation in a variety of organic and inorganic materials. We give several examples of how the spectroscopy can be successfully applied to investigate the photophysics of inorganic and organic materials and corresponding devices. We start with the rare-earth doped metal-oxide structures used in plasma display applications, where we found thermally stimulated increase of the luminescence, as opposed to the expected temperature quenching of the emission . Then we move to the nature of the photoinduced charge carriers in conjugated polymers that is currently the subject of an intense debate. We investigate the main question of whether photoexcitation results in localized excitons or directly leads to mobile charge carriers. We show that charge-carriers are created indirectly through field-induced ionization of excitons . Finally, by studying and correlating the photoexcitation spectra of several observables connected with excitons and charge transport we are able to gain new insights into the nature of the primary photoexcitation in organic molecular crystals. By simultaneously measuring the excitation spectra of the transient photoluminescence and photoconductivity in rubrene single crystals we observed that the free charge carriers are created through a long-lived intermediate state with a remarkable lifetime of up to 0.1 ms and no free carriers appear during the exciton lifetime .
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Host: Vitaly Podzorov