Dynamic Behavior of Electroluminescence from Phosphor-Sensitized Red Fluorescent Organic Light-Emitting Diodes

We study electronic excitation processes in the organometallic phosphor of fac-tris(2-phenylpyridine) iridium(III) (Ir(ppy)(3)) and fluorescent dye of 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)-vinyl]-pyran-4-ylidene}-malononitrile (DCM2) double-doped organic light-emitting devices by using the transient electroluminescent technique. Excitation transfer from Ir(ppy)3 to DCM2 occurs in the device. However, excitons of DCM2 are directly created on DCM2 by charge carrier recombination, and the exciton formation process on DCM2 is preferred over that on Ir(ppy)(3). This probably results from charge carrier trapping on DCM2 in the system. In addition, decay of DCM2 excitons in EL devices was faster than that in the case of photoluminescence. This means that the decay process is influenced by specific processes that occur under electric pumping conditions, such as the exciton-charge carrier annihilation.