Blue organic electrophosphorescence using exothermic host-guest energy transfer

We demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of N,N-'-dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C-2']picolinate (FIrpic). By examining the temperature dependence of the radiative lifetime and the photoluminescence of a film of mCP doped with FIrpic, we confirm the existence of exothermic energy transfer in contrast to the endothermic transfer characteristic of the N,N-'-dicarbazolyl-4-4(')-biphenyl and FIrpic system. In employing exothermic energy transfer between mCP and FIrpic, a maximum external electroluminescent quantum efficiency of (7.5+/-0.8)% and a luminous power efficiency of (8.9+/-0.9)lm/W are obtained, representing a significant increase in performance over previous endothermic blue electrophosphorescent devices. (C) 2003 American Institute of Physics.