The primarily studied transition for Eu 3+ quantum information systems, 5 D 0 → 7 F 0 , is ex-pected to appear for Eu 3+ cations with C 1 or C 2 site symmetry, as in the monoclinic polymorphs, but not for D 3 site symmetry, as in the rhombohedral polymorph. In PL maps, the transition appeared only in mixed symmetry regions (see Supporting Information, Figure ). Polymorph mixing, as reported here, can therefore explain why the 5 D 0 → 7 F 0 transition has been observed for R32 EuGa 3 (BO 3 ) 4 . Also, these PL maps, along with the previously discussed bonding arguments, undermine a second Eu/Al site mixing proposal based on additional lines in low-temperature optical spectra. The article relies on discussions of similar behavior in NdAl 3 (BO 3 ) 4 51,52 that were published before the C2 and C2/c polymorphs were discovered for it. PL maps and spatially-resolved techniques are critical for gaining insight into how crystal quality factors may hinder achieving narrow inhomogeneous linewidths in stoichiometric Eu 3+ materials.