Optical functions of tris (8-hydroxyquinoline) aluminum (Alq(3)) have been studied in the spectral range from 1.55 to 5 eV using spectroscopic ellipsometry. The samples have been deposited by thermal evaporation on glass substrates. Optical functions of Alq(3) deposited on unheated substrates and on substrates kept at 100 degreesC have been determined. The influence of atmosphere exposure to the optical properties of the Alq(3) films has been investigated by photoluminescence measurements, absorption measurements, and spectroscopic ellipsometry. It has been found that the substrate temperature during evaporation affects the environmental stability of the films.