New off‐centre system. Jahn‐Teller mercury‐like impurities in alkali halides

Abstract

AbstractTwo slow decay components are found in the low‐temperature decay kinetics of the AT emission of Ga+ and In+ centres in alkali halides. The emission, excitation, and polarization spectra of these components as well as the temperature dependences of their decay times and light sums and the influence of the electric and magnetic fields on the decay kinetics of the polarized AT emission are carefully investigated. It is shown that the observed effects are caused by an off‐centre position of Ga+ and In+ ions in the triplet relaxed excited state (RES). The off‐centre displacement occurs most probably in one of the 〈100〉 directions perpendicular to the tetragonal Jahn‐Teller distortion axis. Rapid tunnelling transitions between various energetically equivalent off‐centre positions of the impurity ion lead to the tunnel splitting of each metastable tetragonal (T) minimum of the triplet RES. Both the observed slow decay components of the AT emission are connected with the radiative decay of the two lower states. The orthorhombic structure of the AT RES, found by the technique of optical detection of electron spin resonance (OD ESR) several years ago for Ga+ centres in some alkali halides, is explained here as another evidence of the same phenomenon.