RAMAN STUDY ON $X_i^-$(Pb) CENTERS IN SINGLE CRYSTALS OF ALKALI HALIDES DOPED WITH LEAD

Low frequency modes were observed in a series of alkali halides doped with lead after X-irradiation at 77K. The peak positions of the Raman signals are at 34cm^-1 for NaCl:Pb²⁺, 30cm^-1 for KCl:Pb²⁺,28cm^-1 for RbCl:Pb²⁺ and 22cm^-1 for KBr:Pb²⁺. They are assigned to the inelastic light scattering caused by the local vibration of $X^-_i$(Pb⁺) center, which consists of an interstitial halogen ion stabilized by a substitutional ion Pb⁺ . Polarized Raman measurements and Behavior Typer(BT) analysis show that the symmetry of the $X^-_i$ (Pb⁺) center belongs to the point group C_3v. A structure model of the $X^-_i$ (Pb⁺) center is proposed based on the Raman data and the result of BT analysis.