Elasto- and electro-optical dipole properties of off-center Ag+ defects in RbI

Abstract

Electric dipole properties of off-center Ag+ defects, introduced by a diffusion technique, were investigated in RbI. After rapid quenching and cooling the absorption spectrum consists of 4 UV bands at 4.82, 4.92, 5.12 and 5.47 eV. Their oscillator strength slightly decreases then rises with increasing temperature. Weak zero moment changes in all bands were observed when high electric field was applied along the <110> and <111> directions only. No effect occurs along <100>. The sign of the effect allows the determination of the main state of polarization of the bands: perpendicular to the dipole axis for the 4.82 and 5.12 eV, parallel to it for the 4.92 and 5.47 eV. Two models which fit equally well the results are discussed: a <111> dipole model and a restrictive <110> model with 90° reorientation only. They lead to a dipole moment of 1.16 eÅ, respectively 1.34 eÅ if polarization of the bands is assumed. Several arguments favor the <111> model with deep off-center wells for Ag+ in RbI.