RESONANCE RAMAN-SCATTERING OF THE SELF-TRAPPED EXCITON IN ALKALI-HALIDES

We have studied resonance Raman scattering of the self-trapped exciton (STE) in NaCl tuned to the sigma(g) --> sigma(u) hole transition and to the 1s --> 2p electron transition. The former spectrum is characterized by a sharp line at 366 cm-1, which coincides with the stretching-vibration frequency of the H center, while the latter is characterized by broad bands, similar to that of the F center, situated below the LO phonon frequency. The result provides evidence that the STE is essentially an interacting F-H pair.