Understanding this complex polymorph mixing requires spatially-resolved techniques. Though several photoluminescence studies on RX 3 (BO 3 ) 4 have been conducted, none has mapped behavior across a crystal to assess inhomogeneity. The effects of polymorph domains should readily be seen through changes in the 5 D 0 → 7 F 1 transition of Eu 3+ . Photoluminescence spectroscopy can resolve crystal field splits due to the Eu 3+ site symmetry. For the three EuAl 3 (BO 3 ) 4 polymorphs, the Eu 3+ site symmetries are D 3 for R32, C 1 and C 2 for C2, and C 2 for C2/c. For the trigonal point group D 3 , two levels are expected, and for the monoclinic C 2 and triclinic C 1 , three levels. Since no site symmetry should produce more than three levels, the presence of more indicates a site symmetry mix.