Time-resolved measurements of the external electric field effects on fluorescence in electron donor and acceptor pairs of N-ethylcarbazole and dimethyl terephthalate doped in a polymer film

Electric-field-induced change in fluorescence decay has been measured for electron donor and acceptor pairs of N-ethylcarbazole (ECZ) and dimethyl terephthalate (DMTP) doped in a polymer film. Field-induced change in lifetime of the fluorescence emitted from the locally excited state of ECZ clearly shows that the electron transfer from the excited state of ECZ to DMTP is enhanced by an external electric field (F). A comparison is made between the experimental results of the field effect on decay profile of the ECZ fluorescence and the simulated results. Time-resolved electrofluorescence spectra as well as the field-induced change in decay profile of exciplex fluorescence show that exciplex fluorescence is quenched by F at the early stage of time following photoexcitation, but enhanced by F at a later stage of time. Both the decrease in the initial population of the fluorescent exciplex and the lengthening of the exciplex fluorescence in lifetime are shown to be induced by F.