New Insights into the Influence of the 4f55d1 State in the 4f6 Electronic Configuration of Sm2+ in Crystal Hosts.

The use of the Sm2+ luminescence properties in numerous applications appeals for a better understanding of its electronic structure. This work compares luminescence data and crystal field parameters from 31 Sm2+-containing compounds to assess the effects of the crystal field on its energy levels. In particular, the relationship between the 5D0-7F0 and 5D0-7F1 transition energies is analyzed and compared with previously published data for the isoelectronic Eu3+. It appears that for Sm2+, in contrast to Eu3+, the energy of the 5D0 state cannot be considered to be constant and implies the involvement of an extra state (presumably the 4f55d1 level) in the mixing of the 4f6 states. On the other side, the total crystal field strength is correlated to the splitting of the 7F1 states for both Sm2+ and Eu3+ in lower symmetry environments. The plot of the 5D0-7F0 energy as a function of the 7F1 splitting clearly evidences the mixing of the 4f6 state with the environment-sensitive 4f55d1 state for Sm2+, which is finally confirmed by the discrepancy of the ratio between the 5D1 and 7F1 splittings from its theoretical value in the absence of any mixing with the 4f55d1 state.