Optical Properties of 3,4,9,10-Perylenetetracarboxylic Dianhydride and 8-Hydroxyquinoline Aluminum Salt Films Prepared by Vacuum Deposition

Abstract

The main purpose of this paper is to investigate the optical properties of PTCDA and Alq3 films, prepared by two steps, vacuum evaporation and deposition processes on platelets of glass, quartz, and indium-tin-oxide (ITO) coated glass. We have emphasised the bands structure of the absorption spectra with peaks situated at 358 nm, 374 nm, 475 nm and 552 nm in PTCDA, respectively 232 nm, 261 nm and 380 nm in Alq3 that confirms the dominant presence of Alq3 meridianal molecular isomer. For PTCDA films deposited on glass coated with ITO, the structure of the weak double peak at low wavelength is partially modified, but the positions of the two important absorption peaks situated at 2.25 eV and 2.61 eV are unchanged. The two different luminescence emission peaks obtained in Alq3 for different excitation wavelengths (λ=360 nm and λ=520 nm) suggest the existence of the facial isomer beside the meridianal one. We have evidenced a significant Stocks shift in the spectra (EPTCDA=0.40 eV; EAlq3=0.9 eV) and a large Frank- Condon shift (0.40-2.3 eV), suggesting important effect associated respectively with the solid state structure and important conformational differences between the ground and excited state.