Optical detrapping of charge carriers in undoped and in tetracene-doped anthracene crystals

Abstract

The optical release of trapped charge-carriers in undoped and in tetracene-doped (10−6 mole/mole) anthracene crystals is investigated. There processes can be distinguished: 1) Release by mobile anthracene triplet excitons where the triplet absorption spectrum is observed. 2) Release by direct optical excitation of an allowed electronic transition of positive tetracene and anthracene ions (tetracene and distorted anthracene molecules charged with a trapped hole), at γ = 865 and 765 nm, respectively, and subsequent relaxation of the excited hole into the valence band. 3) Release in a broad IR spectral region showing a) negative peaks due to absorption losses into higher anthracene vibrational levels and b) a number of weak peaks with a mean separation of 144 cm−1 tentatively interpreted as phonon satellites.