Structural and optical properties of ε-phase tris(8-hydroxyquinoline) aluminum crystals prepared by using physical vapor deposition method

Abstract

Crystals of ε-phase tris(8-hydroxyquinoline) aluminum (ε-Alq3) were prepared by using physical vapor deposition (PVD) method in a double zone tube furnace. The structural properties of the ε-Alq3 crystals were investigated by using an X-ray single crystal diffractometer (XSCD) and a high resolution scanning electron microscope (SEM). Large straight steps were observed from the side face of the pine needle-like crystals. The straight steps are parallel with each other like terraces and the widths of the steps are fixed, indicating that the ε-Alq3 crystals may have layered structures. The photoluminescence (PL) spectra at different temperatures (7K, 66K, 220K, 300K and 350K) and the absorption spectrum were also investigated. The optical band gap of the ε-Alq3 crystals was calculated to be about 2.82eV. This value is a little larger than that of amorphous mer-Alq3 (about 2.7eV), indicating a minimizing of impurities, grain boundaries and defects.