Absorption spectroscopy of R3+ (R = Pr, Nd) ion pairs in CsCdCl3

The energy levels of R3+(R=Pr,Nd) ions replacing the divalent Cd2+ ions in single crystals of CsCdCl3 have been investigated by polarized absorption at 10 K. For charge balance, a majority of R3+ ions in CsCdCl3 form pairs with a vacancy associated with it. The analysis reveals that R3+ pair ions are in two unequal sites which result from two arrangements: (i) with a vacancy in between the two R3+ ions and (ii) with a vacancy on any one side of the two R3+ ions. Indeed two types of spectra are observed due to the different C-3 upsilon crystal fields at these two sites. Thirteen levels of Pr3+, arising out of five multiplets, and thirty levels of Nd3+, arising out of twelve multiplets, have been identified along with their irreducible representations. The best free-ion and crystal-field parameters for Pr3+ have also been determined.