Pressure-Induced d- to f-Orbital Energy Crossover in Sm2+ Ion in CsSmI3: A Luminescence Study

The divalent samarium ion has a 4f6 configuration. Its energy level diagram resembles that of its isoelectronic ion Eu3+. On the other hand, the lowest excited state of the 4f55d1 configuration with energy analogous to the lowest excited state of the 4f6 configuration, 5D0, also exists. This factor alters the luminescence properties of the Sm2+ ion in host crystals. Broad luminescence bands in the visible and/or the near-infrared regions should be observed for the transition from the 4f55d1 configuration to the ground state. It is well known that if the excited level 5D0 in the 4f6 configuration is lower in energy than the lowest level of the 4f55d1 configuration, then the sharp luminescence bands from the f-f transitions can be observed. As reported earlier from studies with alkaline-earth fluorides, the luminescence lines of Sm2+ are very sensitive to the host crystal for the transition between the 4f55d1 and 4f6 configuration. Pressure effects on the different optical transitions of Sm2+ -doped SrF2 have also been studied recently, and it was reported that pressure has a larger effect on the transition between the 4f55d1 and 4f6 configurations than on those within the 4f6 configuration.