DISORDER INFLUENCED OPTICAL-PROPERTIES OF ALPHA-SEXITHIOPHENE SINGLE-CRYSTALS AND THIN EVAPORATED-FILMS

We report measurements on steady state and time resolved photoluminesc ence (PL) and PL-excitation (PLE) of sexithiophene single crystals and evaporated thin films. In contrast to the broad spectral features usu ally observed even in crystals, we have observed for the first time sh arp emission peaks from the single crystal superimposed on a broader b ackground. The broad background is due to emission from defect states, which are observable in PLE measurements and site-selective FL. These defect states are visible both in films and crystals, but their densi ty and nature are strongly dependent on the growth conditions. Additio nally in the film a fast energy transfer from the primary excited mole cular states to defect states is observed on a sub 100 ps timescale wh ereas the fluorescence lifetime of these defects is around 700 ps. (C) 1998 Elsevier Science B.V.