Crystal Growth of Ternary NaRESe ₂ (RE = Sm, Gd–Lu) Using the Boron Chalcogen Mixture (BCM) Method: Magnetism in Triangular Lattices and Optical Properties

A series of NaRESe2 (RE = Sm, Gd–Lu) compounds were synthesized as single crystals, and NaRESe2 (RE = Ce, Pr, Nd) was synthesized as polycrystalline powders using the boron chalcogen mixture (BCM) method. The detailed synthesis, single-crystal structure characterization, magnetic properties, and optical properties of the NaRESe2 series are reported. The structures of the crystals were characterized by single-crystal X-ray diffraction. This series crystallizes in the trigonal (R̅3m) crystal system, where the RE3+ ions form a triangular lattice. Magnetic property measurements of NaRESe2 (RE = Ce - Nd, Sm, Gd - Yb) indicate the presence of possible antiferromagnetic correlations that were observed in all compounds; however, no long-range magnetic order was observed, suggesting the presence of magnetic frustration. The band gap energies of NaRESe2 (RE = Ce - Nd, Sm, Gd- Lu) were determined by UV–vis diffuse reflectance measurements. NaRESe2 (RE = Gd, Tb, Lu) were shown to luminesce; photoluminescence quantum yield (PLQY) measurements were performed on polycrystalline samples of NaRESe2 (RE = Gd, Tb, Lu).