Prismatic crystal field stabilized divalent rare-earth chalcogenide REIIBII6CIII6QVI16 with bifunctionality

Divalent rare-earth (RE2+) compounds with unique electronic configurations have been known for more than 100 years, and many efforts have been done, but the synthesis of inorganic RE2+ chalcogenides is still a challenge due to the chemical instability of RE2+. Herein, nine new RE2+ chalcogenides REIIBII6CIII6QVI16 (REII = La, Ce, Pr, Yb; BII = Mg, Mn; CIII = Al, Ga; QVI = S, Se) have been rationally designed in an octahedra and tetrahedra composed flexible framework, and fabricated in experiment. In the nine compounds, RE2+ is stabilized by a prismatic crystal field, rather than the common octahedral crystal field. The compounds, especially for the sulfides, exhibit significant luminescence properties with wide visible light emission bands under the excitation of ultraviolet source. Meanwhile, the representative LaMg6Ga6Se16 exhibits a strong nonlinear optical (NLO) response of 1.5 × AgGaS2 (AGS), and a high laser-induced damage threshold (LIDT) of 3 × AGS. The results demonstrate that the RE2+ chalcogenides are bifunctional compounds, enriching the chemical diversity of RE materials, and opening an avenue for the design of new functional materials with RE2+ based on the stable and flexible inorganic anionic frameworks.