We have explored several new stoichiometric candidates for optically addressable quantum memory systems that would not require isotopic enrichment and that have a large europium separation. We initially proposed 33 theoretical structures with 19 unrealized compositions. We then showed that using fully relativistic 4f 6 and 4f 7 frozen-core pseudopotentials for Eu 3+ and Eu 2+ , respectively, provide accurate predictions of europium system ∆H f values. Using DFT calculations, we predicted that six of the unrealized compositions have a stable polymorph, including Eu 2 P 4 O 13 , which, unknown to us beforehand, has been synthesized.