Photoluminescence study of BEDT-TTF and its ion radical salt

Photoluminescence spectra of the organic donor compound, bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), has been observed in crystals and rigid solution at liquid He temperature. The spectra have similar shape with a maximum at 1.96 eV and an intense side-band near 1.79 eV. A solid state effect reveals itself in low-temperature excitation spectra of the crystalline sample as a drastic increase of the excitation efficiency in the low energy region (2.1–3.1 eV) comparing to the high energy one (3.1–4.0 eV). The emission of BEDT-TTF is quenched by a modification of degree of oxidation of molecules forming the crystal and is very weak in the case of monovalent (BEDT-TTF)Br salt. The recorded spectra are interpreted assuming a dimer-like arrangement of molecules in the investigated compounds.