Delayed fluorescence and phosphorescence of tris-(8-hydroxyquinoline)aluminum (Alq3) and their temperature dependence

This paper reports on delayed luminescence measurements of tris-(8-hydroxyquinoline)aluminum (Alq3) after optical excitation; these identify two bands in the emission spectrum: delayed fluorescence and phosphorescence. This is shown for different crystalline phases and for evaporated films. The assignment of the low-energy band to the phosphorescence is confirmed by lifetime measurements, and triplet energies of the meridional isomer in the α-phase and the facial isomer in the δ-phase are determined from the well-resolved vibronic progressions of the phosphorescence as 2.11±0.1 and 2.16±0.1 eV, respectively. Lifetimes of the delayed fluorescence and the phosphorescence are determined for a temperature range from 6 to 150 K, and we measured the temperature dependence of the delayed photoluminescence spectra.