The orientation behavior and mechanism of REBa 2 Cu 3 O (RE123) films have not been clarified yet. We prepared RE123 films by the pulsed laser deposition method and investigated the orientation behavior and mechanism. We argue that the orientation behavior strongly depends on thermodynamic parameters such as the heat of sublimation. The thickness and surface morphology dependences of the orientation suggest that -axis oriented thicker films will be obtained in RE123 if the surface remains smooth up to objective thickness. Critical temperatures were around or higher than 90 K and critical current densities were larger than 1 MA/cm 2 for all RE123 films. From the viewpoint of the orientation, the Yb123 films were the easiest to grow with the -axis normal to the substrate surface.
The authors prepared an organic electroluminescent diode (organic LED) with hole transport material and aluminium quinoiline and another organic LED with an additional electron blocking layer using the DCM partial doping method. The authors studied the change in the EL spectra accompanied by the applied current in the specimens by means of the peak separation method. The electron-hole recombination did not always occur at the emission layer near the interface between the hole transport layer and the Alq3 emission layer from the initial EL stage after electrons had been transported from cathode to the interface. It was proved that the emitting region is shifted from the cathode side to the anode side in the emission layer with increasing applied current, especially by electron injection from the cathode. In addition, from the measurement of the specimen with an electron blocking layer, the authors found that the dominant EL process is not due to the carrier trap model in an organic DCM-doped Alq3 LED.
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.
The organic electoluminescent diode (LED) with squarylium (Sq) dye-doped Alq3
changes color upon application of voltage (current). The luminescent color from the
organic LED changes from red (electroluminescence (EL) of Sq dye) at low voltage to
light green (EL of Alq3) at high voltage. We studied the EL efficiency and EL spectrum
of organic Sq-doped Alq3 LED with various doping positions in the emission layer.
Consequentially, it was clarified that Sq doping near TPD considerably reduced the
EL efficiency. The EL mechanism of the organic LED was concluded to be associated with
the energy transfer from the excited Alq3 to the guest dye and hole trapping of the guest dye in Alq3.
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