Electroplex emission from a layer of a mixture of a europium complex and tris 8-quinolinolato/aluminum

With a europium complex, tris a-thenoyltrifluoroacetonato.bis triphenylphosphine oxide. europium Eu TTA.3 TPPO.2., as the light-emitting layer, N, NX-diphenyl-N, NX-di m-tolyl.-benzidine TPD.as the hole transport layer and tris 8- quinolinolato.aluminum ALQ. as the electron transport layer, the triple-layer electroluminescent EL. device emits red light characteristic of Eu3q emission. However, as the mixture of Eu TTA.3 TPPO.2 and ALQ is co-evaporated as the light-emitting layer to form a bilayer EL device, a new wide-banded emission peaked at c. 640 nm was obtained. This emission is neither from ALQ nor from the europium complex. The photoluminescence PL. of the thin film on quartz substrate evaporated from one mixed solid powder of Eu TTA.3 TPPO.2and ALQ is composed of distinct PL emissions of Eu TTA.3 TPPO.2and ALQ, denying an exciplex formation mechanism. It is impossible to form a host–guest system. We propose that the EL emission peaked at c. 640 nm is from an electroplex route: a transition between the lowest unoccupied molecular orbital LUMO.of Eu TTA.3 TPPO.2 and the highest occupied molecular orbital HOMO.of ALQ. q2000 Elsevier Science B.V. All rights reserved.