Abstract

We prepared organic light emitting diodes (LEDs) with alternately deposited dye-doped aluminium quinoline (Alq3) and diamine derivative (TPD), and studied their electroluminescence (EL) and photoluminescence (PL) properties. The alternate deposition structure changed the energetic position and full width at half maximum (FWHM) of the EL spectra for the organic LED with alternately deposited undoped Alq3 layers, but did not change those for the organic LED with alternately deposited dye-doped Alq3 layers. On the other hand, the EL efficiency of the dye-doped specimens, despite the use of sample dyes with high PL quantum yield, was lower than that of the undoped specimen. Although the location of an emitting Alq3 layer depends on electron injection, the emitting region in a 5 nm thick Alq3 layer was estimated to be localized near the TPD layer on the anode side by a partial dye-doping method. To explain the conflict between the electron injection dependence of EL and the location of the emitting region, we propose recombination in the TPD layer and the direct energy transfer from TPD to the sample dye without the excitation of Alq3.

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