Vibronic intensities for Er3+ in Cs2NaErCl6

In this current study, we have undertaken vibronic intensity calculations f or the absorptions \(I-4(15/2))Gamma (k)> --> \(I-4(13/2))Gamma (l)> of the Er3+ in the Cs2NaErCl6 elpasolite type system. This system is extremely co mplicated to handle from both a theoretical and an experimental viewpoints. This theoretical work shows that over an energy range of about 400 cm-l, a substantial amount of transitions are likely to take place (about 100 tran sitions; twenty five of them are magnetic dipole allowed and seventy five a re vibronically allowed). It is then a formidable task to identify and assi gn all of these transitions in a non-ambiguous way. Also the experimental e vidence available for these absorptions is related to a total of about twen ty lines in the luminescence spectrum of this system. The spectrum itself i s very challenging and the superposition of spectral features is most likel y to occur. A careful analysis of the calculated vibronic intensities and o verall oscillator strengths for the various transitions indicates that the current model used is both flexible and appropriate to deal with this kind of systems. In a forthcoming paper, we will examine the rather unusual high intensity associated with the \(I-4(15/2))Gamma (k)> --> \(S-4(3/2))Gamma (l)> excitations.