Nonlinear Raman spectroscopy of the low-lying levels of the Sm2+ ion doped in SrF2 and CaF2 crystals

We used coherent anti-Stokes Raman scattering (CARS) spectroscopy to study the symmetry of the low-lying levels of the Sm2+ ion doped in sites of cubic (Oh) symmetry in the SrF2 and CaF2 matrices. Taking advantage of the polarization sensitivity of the Raman spectroscopic techniques, we confirm that the line at ≈652 cm-1 (that we could only observe in the SrF2 case because of wavelength limitations) corresponds to excitation from the ground (4f6 7F0) A1g level to the Stark T2g level originating from the splitting of the (4f6 7F2) multiplet. In the same SrF2 sample, the (4f6) 7F0→ 7F1 transition was observed to be weaker. In CaF2 matrices in which it is more easily detected, we checked its T1g symmetry.