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

The use of the Sm 2+ 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 Sm 2+ -containing compounds to assess the effects of the crystal field on its energy levels. In particular, the relationship between the 5 D 0 - 7 F 0 and 5 D 0 - 7 F 1 ransition energies is analyzed and compared with previously published data for the isoelectronic Eu 3+ . It appears that for Sm 2+ , in contrast to Eu 3+ , the energy of the 5 D 0 state cannot be considered to be constant and implies the involvement of an extra state (presumably the 4f 5 5d 1 level) in the mixing of the 4f 6 states. On the other side, the total crystal field strength is correlated to the splitting of the 7 F 1 states for both Sm 2+ and Eu 3+ in lower symmetry environments. The plot of the 5 D 0 - 7 F 0 energy as a function of the 7 F 1 splitting clearly evidences the mixing of the 4f 6 state with the environment-sensitive 4f 5 5d 1 state for Sm 2+ , which is finally confirmed by the discrepancy of the ratio between the 5 D 1 and 7 F 1 splittings from its theoretical value in the absence of any mixing with the 4f 5 5d 1 state.