Excitation dynamics of dye doped tris(8-hydroxy quinoline) aluminum films studied using time-resolved photoelectron spectroscopy

In this work, we use excite-probe photoelectron spectroscopy to study the decay of electronic excitation in tris(8-hydroxy quinoline) aluminum (Alq) doped with the organic dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). Ultrashort laser pulses are used to photoexcite electrons into unoccupied molecular orbitals, and the ensuing decay rate is directly observed using photoelectron spectroscopy. Decay of the electronic excitation is studied as a function of DCM doping percentage and excitation intensity. The decay rate is seen to increase with both doping percentage and excitation intensity. These data are explained using a model including Forster transfer, stimulated emission, concentration quenching, and bimolecular singlet-singlet exciton annihilation. In this model, we find that it is necessary to include a very fast (faster than predicted in standard Forster transfer theory) excitation transfer of a fraction of the excitation from the Alq to the DCM, where that fraction corresponds to the approximate nearest-neighbor population. (C) 2001 American Institute of Physics.