BIMOLECULAR REACTIONS OF SINGLET EXCITONS IN TRIS(8-HYDROXYQUINOLINE)ALUMINUM

We have studied singlet excited state dynamics in thin films of tris(X -hydroxyquinoline) aluminum (Alq3), a well known emitter for organic e lectroluminescent devices. Our experimental results show that bimolecu lar recombination dominates the singlet exciton decay in pristine film s at high intensities, thus decreasing the photoluminescence quantum e fficiency and the singlet lifetime. Because of the relatively low carr ier concentration at which light emitting diodes operate the electrolu minescence efficiency is not affected. The measured rate constant of s inglet-singlet annihilation in AIq3 films is gamma(ss)=(3.5+/-2.5)x10( -11) cm(3) s(-1). The diffusion coefficient and the diffusion length o f singlet excitons estimated from gamma(ss) are D-s=(1.2+/-0.8)x10(-5) cm(2) s(-1) and L=98+/-40 Angstrom, respectively. (C) 1996 American I nstitute of Physics.