Electric-Field Effects on Hole Spectra in Doped Polymers: A Step towards Two-Dimensional Optical Spectroscopy

Abstract

Optical absorption bands of organic dye molecules or inorganic ions in condensed matter are affected by inhomogeneous broadening [1] and are thus usually much broader than the corresponding homogeneous lines. In disordered systems, the difference can amount to several orders of magnitude at low temperatures. In order to detect the effects of external perturbations such as hydrostatic pressure or electric fields on an inhomogeneous band, the perturbations must therefore have very large magnitudes. The sensitivity can be greatly enhanced by investigating the changes of hole-burning spectra caused by the external fields. In amorphous matrices, an external electric field gives rise to a symmetrical broadening of spectral holes due to the linear Stark effect. This was shown to be true even in the case of centrosymmetric dopant molecules where the first-order Stark effect is ascribed to matrix-induced dipole moments [2] (see Fig. 1). The magnitude of the broadening yields thus information on the electrostatic dye-matrix interaction.