Fluorescence Lifetime of Organic Thin Films Alternately Deposited with Diamine Derivative and Aluminum Quinoline

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Abstract
Fluorescence lifetimes of organic thin films alternately deposited with diamine derivative (TPD) and aluminium quinoline (Alq3) were measured. The alternating deposition structure was shown to enhance the emission from Alq3 in spite of imperfect film structures. Energy transfer from TPD to Alq3 was evidenced by the correlation between lifetime and period number. It was found to be a competitive process with the TPD radiation process, and its rate of TPD radiation was estimated to be 1.2×1010 s-1. The authors suggested that the presence of the region mixed with TPD and Alq3 at the TPD/Alq3 interface plays an important role in the electroluminescence (EL) process. The Alq3 exciton confinement was clarified experimentally since the component of the faster fluorescence lifetime of Alq3 increased in the short-wavelength region. In addition, the authors proposed a possible EL model based on the suppression of the thermal inactivation of Alq3 excitons during their diffusion.