Electrical and Optical Properties of Thin Film and Superlattice Structure Utilizing Conducting Polymers and Their Application for Luminescent Devices

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Novel electroluminescent (EL) characteristics and quantum size effects in organic multiple quantum well (MQW) structure have been discussed. Unique EL spectrum and polarization characteristics have been discussed in organic MQW systems. The experimental results are summarized as follows.1)Energy transfer has been observed in aluminum quinoline (Alq_3) /aromatic diamine (TPD) MQW system, where the strong photluminescence (PL) emission has been observed from Alq_3 layr in the short-period MQW structure. PL energy shift to higher energy side has been observed in the short-period MQW structure, which is caused by quantum size effect in the MQW structure.2) The PL intensity is quenched by applying reverse biased electric field to the Alq_3/TPD MQW system. The quenching is strong in the short-period structure, where the extraction of exciton is strong due to the strong electric field in the Alq_3 layrs.3) The PL spectrum with cyclopentadiene derivatives (PPCP) /aromatic diamine (TPD) MQW structure exhibits a peak emission from PPCP.Since the spectrum of the MQW system does not depend upon the excitation light, it is interpreted that the energy transfer from TPD to PPCP has been conducted and the excitons are confined in the PPCP layr.4) The EL spectra of the diodes with PPCP/TPD MQW structure exhibits only from PPCP.In the short-period stucture, newly created emission at longer wavelength is observed besides the original emission of PPCP.This is caused by the interaction or the interface of the thin layrs, and the interaction between the layrs are strong in this system. TE mode has the shorter wavelength component and TM mode the longer one.