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 ${\mathrm{\sigma }}_{\mathrm{g}}$→${\mathrm{\sigma }}_{\mathrm{u}}$ hole transition and to the 1s→2p electron transition. The former spectrum is characterized by a sharp line at 366 ${\mathrm{cm}}^{\mathrm{-}1}$, 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.