  Biluminescent organic emitters show simultaneous fluorescence and
phosphorescence at room temperature. So far, the optimization of the room
temperature phosphorescence (RTP) in these materials has drawn the attention of
research. However, the continuous wave operation of these emitters will
consequently turn them into systems with vastly imbalanced singlet and triplet
populations, which is due to the respective excited state lifetimes. This study
reports on the exciton dynamics of the biluminophore NPB
(N,N-di(1-naphthyl)-N,N-diphenyl-(1,1-biphenyl)-4,4-diamine). In the extreme
case, the singlet and triplet exciton lifetimes stretch from 3 ns to 300 ms,
respectively. Through sample engineering and oxygen quenching experiments, the
triplet exciton density can be controlled over several orders of magnitude
allowing to studying exciton interactions between singlet and triplet
manifolds. The results show, that singlet-triplet annihilation reduces the
overall biluminescence efficiency already at moderate excitation levels.
Additionally, the presented system represents an illustrative role model to
study excitonic effects in organic materials.
