Effect of Electric Field on Coulomb-Stabilized Excitons in Host/Guest Systems for Deep-Blue Electrophosphorescence

Here, a study of the electric field induced quenching on the phosphorescence intensity of a deep-blue triplet emitter dispersed in different host materials is presented. The hosts are characterized by a higher triplet excitonic level with respect to the emitter, ensuring efficient energy transfer and exciton confinement, whereas they differ in the highest occupied molecular orbital (HOMO) alignment, forming type I and II host/guest heterostructures. While the type I structures shows negligible electric field induced quenching, a quenching up to 25% for the type II at a field of 2 MV/cm is reported. A similar quenching behaviour is also reported fro thin films of the pure emitter revealing an important luminescence loss mechanism for aggregated emitter molecules. These results are interpreted by considering Coulomb stabilized very sensitive to dissociation upon application of the field. These results clarify the role of external electric field quenching on the phosphorescence of triplet emitters and provide useful insights for the design of deep-blue electrophosphorescent devices with a reduced efficiency roll-off.