Excitonic singlet-triplet ratio in a semiconducting organic thin film

A technique is presented to determine the spin statistics of excitons forme d by electrical injection in a semiconducting organic thin film. With the a id of selective addition of luminescent dyes, we generate either fluorescen ce or phosphorescence from the archetype organic host material aluminum tri s (8-hydroxyquinoline) (Alq(3)). Spin statistics are calculated from the ra tio of fluorescence to phosphorescence in the films under electrical excita tion After accounting for varying photoluminescent efficiencies, we find a singlet fraction of excitons in Alq(3) of (22 +/- 3)%. [S0163-1829(99)08743 -3].