Electronic spectra and crystal field analysis of Yb2+ in SrCl2

The 10 K emission spectrum and absorption spectrum between 27 000 and 30 000 cm(-1) have been recorded and assigned for SrCl2:Yb2+ (0.05 and 1 at. %), where the divalent ion is situated at a site of O-h symmetry with eightfold coordination to chloride ions. In emission, two broad bands are observed at room temperature and these are assigned to orbitally forbidden and allowed transitions from 4f(13)5d to the 4f(14) ground state S-1(0). Nearly all of the transitions, except for some of the highest energy absorption bands, are spin forbidden in the sense that the transition final states are dominated by spin triplet components, while the initial state is a pure spin singlet. The spectral intensities in the absorption spectrum have been fitted satisfactorily, following the crystal field calculation for 4f(13)5d in which four parameters were freely varied. There is no need to cite the presence of Yb2+ ions at several sites in order to explain the observed absorption bands, as has been done previously, but we invoke the coparticipation of the (low-lying) 4f(13)6s configuration. The rationale for the parameter values is explained in detail as are the effects of parameter variations. The calculated radiative lifetime for the orbitally allowed emission transition is in agreement with that measured at low temperature (similar to 1 mu s) and the nonradiative rate from the luminescent level has been modeled as a function of temperature.