From the proposed materials, we excluded options where the minimum Eu 3+ separation for every polymorph was <3.9 Å to avoid unwanted Eu 3+ cation interactions. We also removed candidates predicted to lie in phase diagrams that were already thoroughly investigated experimentally. These included two fluorides not in published phase diagrams, CsEu 3 F 10 and NaEu 2 F 7 ; 17 Eu-Bi-O compositions in a solid-solution phase region or with non-stoichiometric structures; Eu-Y-O compositions expected to be solid-solutions; and Eu-Al-O compounds not appearing in phase diagrams.