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"The triplet state in tris-(8-hydroxyquinoline)aluminum" M. Cölle, C. Gärditz, M. BraunJ. Appl. Phys. 96, 6133 - 6141 (2004) Abstract: This paper presents the characterization of the triplet state in tris-(8-hydroxyquinoline)aluminum (Alq3). An emission spectrum of Alq3, namely, the phosphorescence, is presented for crystalline and amorphous Alq3, which enables direct investigation of the T1 to S0 transition. The assignment of this spectrum to the phosphorescence is further confirmed by temperature-dependent measurements and comparison with the delayed fluorescence. The triplet energies of the meridional and facial isomer (in α- and δ-Alq3) are determined from the well-resolved vibronic progressions of the phosphorescence as 2.11±0.1 and 2.16±0.1 eV, respectively. Furthermore, the lifetime of the triplet state is measured for a temperature range from 6 to 150 K. These temperature-dependent measurements also identify a so far unknown phase transition of Alq3 at about 50 K. Optically detected magnetic resonance at a zero field is used to measure the characteristic zero-field splitting parameters (E=0.0114 cm-1 and D=0.0630 cm-1), and these are discussed in terms of a molecular symmetry and contribution of different ligands and suggest a mini-exciton-like behavior of the triplet state on the three ligands of the Alq3 molecule. All these measurements are performed on different crystalline phases (α- and δ-Alq3) and on evaporated amorphous films. The differences observed for the δ-phase are consistent with the reduced intersystem crossing and thus with the facial isomer in this phase. BMO authors (in alphabetic order): Markus Braun  WWW-Version |
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Letzte Änderung: 2016-09-14 13:34
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