We successfully synthesized polycrystalline Cs 2 NaEuF 6 . We first combined stoichiometric amounts of CsF (99.9%, Sigma Aldrich), EuF 3 (99.9%, Fisher), and NaF (99.99%, Alfa Aesar) under argon. We then placed them in a carbon-coated quartz tube before sealing the hygroscopic powder under vacuum. We heated the powder at 10 • C/min to 600 • C, held at that temperature for 4 h, and cooled back to room temperature at 10 • C/min. The structure matched the cubic double perovskite structure type used in the DFT calculations (Figure ). The XRD pattern is in Figure , and the refined atomic positions are in Table . The refined lattice parameter is a = 9.1430(2) Å, smaller than the DFT predicted value of 9.2306 Å, and Next, we attempted to grow Cs 2 NaEuF 6 single crystals by melting the starting powders in the carbon-coated tube and slow cooling through the melting point. As the melting point of the mixture is unknown, we attempted to heat the mixture to 700 • C. At this temperature, though, the compound attacks the glass despite the carbon coating, eliminating that route to single crystals. Additionally, EuF 3 is insoluble in water, precluding simple solution precipitation. The most likely routes to high quality single crystals are a hydrofluoric acid solution method or a high-temperature sealed metal tube method.