Crystallization of Amorphous Tris(8-hydroxyquinoline)aluminum Nanoparticles and Transformation to Nanowires

Authors


  • This work was supported by the National Science Council of Taiwan under Contract No. NSC 93-2216-E-007-034 and the Ministry of Education of Taiwan under Contract No. A-91-E-FA04-1-4.

Abstract

Amorphous tris(8-hydroxyquinoline)aluminum (AlQ3) nanoparticles can be grown directly into α-phase crystalline nanowires in a one-step heat treatment. At the most appropriate Ar pressure, heating time, and heating temperatures (between 150 and 190 °C), fine and long nanowires are obtained. The growth of the nanowires is dictated by the anisotropic bonding in α-AlQ3 crystals. The growth mechanism is illustrated by the concept of nucleation and molecular migration. Two exotherms are revealed, from differential scanning calorimetry analyses, in the transformation process of AlQ3 amorphous nanoparticles to crystalline nanowires. The first exotherm is the transition from amorphous nanoparticles to the γ-phase, and the second exotherm is the transition from the γ- to the α-phase. By means of Kissinger plots, the activation energies for the crystallization of the γ-phase and the transition from the γ- to the α-phase are calculated, for the first time, to be 9.7 and 12.1 kJ mol–1, respectively. A blue-shift and higher intensity of photoluminescence after heat treatment are also demonstrated.

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