Optical spectra and crystal‐field analysis of europium double nitrates

Locations and assignments of crystal‐field levels in low‐temperature spectra are reported for Eu3+ in the europium double nitrate system [Eu2M3(NO3)12⋅24H2O with M=Mg, Zn]. These energy levels are assigned from the polarized luminescence and the polarized absorption measurements on single crystals at 77 K. The arrangement of the oxygen atoms around the europium ion has approximate icosahedral symmetry and we have tried to find out whether the spectroscopic properties of Eu2M3(NO3)12⋅24H2O reflects this pseudosymmetry, even though the site symmetry of the europium ion is C3. Quantitative crystal‐field calculations have first been performed assuming a C3v symmetry which is close to icosahedral. The levels are analyzed in terms of 20 free‐ion and 6 crystal‐field parameters. Afterwards it is examined how far the C3v parameters can be used to approximate the C3 symmetry. In this case, three additional imaginary crystal‐field parameters are taken into account.