Effects of electron correlation in crystal-field splittings of Sm2+ in MFCl-type hosts

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.