SPECTRAL INTENSITIES IN CUBIC SYSTEMS - IV - THE CS2NATMCL6 SYSTEM

The absorption and emission spectra of the cubic elpasolite Cs2NaTmCl6 in the near infrared range from 4100 cm(-1) to 8600 cm(-1) have been reported previously. The absorption transitions involve the H-3(6) gro und state, the F-3(4) and H-3(5) excited free ion electronic states, w hereas the emission excitations involve the initial H-3(4), H-3(5) and F-3(4) terms. For the first time, we report explicit calculation for the vibronic intensities associated with the emission H-3(4)(Gamma(i)) --> F-3(4)(Gamma(1)). We have chosen this transition so that to illus trate the effect of the inclusion of several relativistic terms in the electronic hamiltonian for the system. Throughout the course of the p resent work, we examine the role played by the various order of approx imations in the calculated relative vibronic intensity calculation. We shall show that these results are unexpected and the most important f eatures of the spectra can be explained reasonably well using a few pa rameters model for this system. Extensions of the current model are gi ven in detail in the text.