Photoluminescence quenching of tris-(8-hydroxyquinoline) aluminum thin films at interfaces with metal oxide films of different conductivities

We report a comprehensive study of photoluminescence (PL) quenching of tris-(8-hydroxyquinoline) aluminum (Alq[subscript ]3) at interfaces with thin films of tin oxide (SnO[subscript 2]) using both steady-state and time-resolved measurements. Quenching of excitons generated in the Alq3 layer increased with increased conductivity of the SnO[subscript 2] films, which we relate with the presence of nonradiative energy transfer from excitons in Alq[subscript 3] to transitions in SnO[subscript 2]. In addition, due to the semitransparency of SnO[subscript 2], the effects of optical interference on the steady-state PL quenching of Alq[subscript 3] are determined. We demonstrate that without accounting for the interference effects in the excitation, the extracted exciton diffusion length (L[subscript d]) in Alq3 is in the range of 10–20 nm. However, when using a numerical model to account for the optical interference effects, we find that L[subscript d] is in the range of 5–9 nm, which agrees with L[subscript d] extracted from time-resolved measurements (4–6 nm). We conclude that time-resolved measurements are least affected by optical interference, yielding the most accurate measurement of L[subscript d].Department of DefenseNational Science FoundationInstitute for Soldier Nanotechnologie