Resonant Raman scattering by a localized mode in CsI

Resonant Raman scattering by a localized mode with a wave number of 110 ${\mathrm{cm}}^{-1\mathrm{}}$ was observed in additively colored CsI. The defect center, presumably ${\mathrm{I}}_2^{-}$ or ${\mathrm{I}}_3^{-}$, produced observable scattering up to sixth order. The broad resonance enhancement curve peaking in the visible could be defined by a discrete number of lines from Kr and Ar lasers. Peak resonant enhancement for first- and second-order processes occurred at frequencies separated by about ten phonon energies. In addition, the Raman intensity increased sharply with decreasing sample temperature. These unusual features can be explained by a nonradiative loss process in the intermediate electronic state.