Configuration interaction of Pr3+ in PrCl63−

The low-temperature electronic spectra of Pr3+ at an octahedral site of symmetry in the PrCl63− moiety, in crystals of Cs2NaPrCl6, Cs2LiPrCl6, and Cs2NaMCl6:Pr(M=Gd, Y) have been measured and interpreted. Together with the results from d–f emission spectra and resonance electronic Raman spectra, these new data permitted the assignment of symmetry representations of up to 39 out the possible 40 crystal field levels of the 4f2 configuration. The inclusion of configuration interaction with the next highest even parity configuration, 4f6p, into the energy level parametrization reduced the mean deviation of the energy level fit using the single 4f2 configuration model alone, by a factor of 2.9 (i.e., from 32.7 to 11.6 cm−1). In particular, the interaction mechanism for the “anomalous” multiplets D21 and G41 was shown to arise from crystal field mixing with 4f6p states. This leads to the inclusion of up to about 0.5% of fp-orbital character for these 4f2 eigenvectors. In the 4f2 single-configuration fits to triplet levels alone, the fourth-degree crystal field parameter turned out to be larger than in the fits to singlet terms, which is the reverse of the expected order if correlation crystal field effects are important.