Figure 2: Splitting of the 4f65d1 electronic level and crystal structure in Sr1-(x+y)CaxEuyS.
From: Solar spectral conversion for improving the photosynthetic activity in algae reactors

Electronic splitting occurs as a result of increasing crystal field strength 10Dq (a). The normalized X-ray diffraction patterns of the rock-salt structure of Sr1-(x+y)CaxEuyS (b) are shown in c. The values of x and y are indicated in the labels. A shift of the diffraction peaks to larger angles indicates lattice contraction. a.u., arbitrary unit.