MOMENT ANALYSIS OF R2 ZERO-PHONON LINE IN NAF UNDER UNIAXIAL STRESS

The R2 zero-phonon absorption line 4480 Å in NaF at 4.2 °K and 23 °K is studied under uniaxial stress along 〈100〉 and 〈100〉. According to the F3 model of the R center the R2 line is found to be due to a transition between a degenerate ground state (2E) and a nondegenerate excited state (2A) of this center. Instead of a splitting into single components under stress, changes in line shape are observed which are analyzed by means of the method of moments. The zeroth and first moment of the line are calculated as functions of the magnitude of stress and temperature. The theoretical moments are found to be in good agreement with those determined from the experimental data. From a comparison of the measured moments with the theoretical expressions the stress splitting parameters are obtained which describe the removal of both the orientational and the orbital degeneracy of the R center under uniaxial stress. The corresponding strain parameters of the R2 line in NaF are compared with those in other alkali halides. © 1968 Springer-Verlag.