Surface reactions of singlet excitons in solid films of 8-hydroxyquinolinealuminium (Alq(3))

Fluorescence excitation (FE) spectra of Al(III) 8-hydroxyquinoline (Alq(3)) solid films in contact with quartz, metal and some red-emitting dyes were measured and related to the FE spectrum recorded from the uncovered film su rface. Their profiles indicate that singlet excitons are quenched by the su rface and near-surface energy accepters. The quenching efficiency (delta) d ependence on penetration depth (l(a)) of the exciting light is a result of both diffusion of singlet excitons towards the surface and their reactions with exponential distribution of quenching centres in the films. It is poss ible to fit the calculated delta (l(a)) curves to the experimental data if values of the diffusion length of singlet excitons l(d) = 30 +/- 15 nm or t he penetration depth of the quenching centres from the surface into the bul k of the order of 10(2)-10(3) nm are used. Possible origin of quenching cen tres and the quenching effect on quantum electroluminescence yield of organ ic light-emitting diodes based on Alq(3) emitter are briefly discussed. (C) 2001 Elsevier Science B.V. All rights reserved.