Observation of charge transfer states in phenothiazine crystal which have lower energies than Frenkel excitons is reported. Two weak absorption peaks are observed at 15 K around 420 nm (2.9 eV) in the absorption edge, the absorption coefficient of which can be modulated up to a few percent by an external electric field. The modulation is so large, because the transitions are not overlapped with strong exciton absorption bands and susceptible to direct observation. The final states of the transitions have large dipole moments (sim;50 D). The conductivity band gap is estimated to be 3.35 eV.
展开▼
