Singlet to triplet excitation spectrum of thin film tris-(8-hydroxyquinolate)-aluminium in direct absorption

We report the excitation spectrum of a ∼ 185 nm thick layer tris-(8-hydroxyquinolate)-aluminium, vapour deposited on a 100 μ m thick borosilicate microscopy cover glass, in the 1.9–2.4 eV range using a conventional cavity-ringdown spectrometer setup. The spectrum is collected at room temperature in an open cavity. It shows a broad loss structure with a maximum around 2.1 eV and a width of ∼ 0.2 eV. The spectrum is in conformity with literature phosphorescence spectra and with literature TDDFT computed T1← S0 transition energies. The observed loss structure can be attributed to the T1← S0 absorption band of tris-(8-hydroxyquinolate)-aluminium.