Research on novel organic nano-optical materials operating in invisible wavelength regions

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The purpose of this research is to develop organic light-emitting diodes (OLEDs) operating in invisible wavelength regions such as ultraviolet and infrared. We investigated optical properties of organic multiple-thin layers and multiple-quantum well (MQW) structures. The MQW structures consist of two organic low-weight-molecule materials, DCM and TPD. We found that the peak-generating wavelength in photoluminescence (PL) spectra exhibits to be shortened due to quantum size effect in DCM/TPD MQWs. This quantum size effect was also observed in electroluminescence (EL) spectra. The subband energies of electrons in DCM/TPD MQWs are determined by numerical calculation in the context of envelope function approximations. From this, we successfully estimated the effective mass of electrons in DCM QWs as to be about 0.5m_0.We fabricated polymer LEDs (PLEDs) by using a polymer material, PCA, which has the maximum absorption coefficient in the ultraviolet region. A PL spectrum of PCA reveals three peak-generating wavelengths, 395, 510 and 650 nm. This indicates that ultraviolet PLEDs can be fabricated if high-effective carrier injection into the radiative site of 395-nm is realized. The PLED consisting of a PCA single layer exhibits a light emission at 650 nm. However, by introducing a hole-transport layer, the PLED exhibits a light emission at 510 nm.These results indicate that emission wavelengths of OLEDs can be artificially controlled by using organic MQW structures. In addition, we also found PLEDs consisting of a TPD-doped PCA active layer are useful to control the emission wavelength of PLEDs.