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

Crystals of epsilon-phase tris(8-hydroxyquinoline) aluminum (epsilon-Alq(3)) were prepared by using physical vapor deposition (PVD) method in a double zone tube furnace. The structural properties of the epsilon-Alq(3) 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 epsilon-Alq(3) crystals may have layered structures. The photoluminescence (PL) spectra at different temperatures (7 K, 66 K, 220 K, 300 K and 350 K) and the absorption spectrum were also investigated. The optical band gap of the epsilon-Alq(3) crystals was calculated to be about 2.82 eV. This value is a little larger than that of amorphous mer-Alq(3) (about 2.7 eV), indicating a minimizing of impurities, grain boundaries and defects. (C) 2014 Elsevier B.V. All rights reserved.