(a) Isotropic spectra with different crystal field splitting energies. (b) Energy splitting as a function of 10Dq. The grey dashed line corresponds to the condition that the peak energy splitting is equal to 10Dq. The black dot-dash line is reproduced from de Groot et al. (1990). (c) Relative intensities of different excitation peaks a1, a2, b1 and b2 versus 10Dq values. The intensities are normalized by a2 peak intensity calculated at 10Dq = 0 eV.