NaGaSe: An Infrared Nonlinear Optical Material with Balanced Performance Contributed by Complex {[GaSe]} Anionic Network.

Second-order nonlinear optical (NLO) materials are extensively applied in laser-related techniques. For developing IR NLO materials, chalcogenides are the main candidates. Here, NaGaSe was explored as inspired by its unique anionic structure. It crystallizes with the orthorhombic chiral 222 structure, featuring 12 types of GaSe tetrahedra built into a three-dimensional {[GaSe]} anionic network, representing a new NLO-functional motif. NaGaSe exhibits large and phase-matchable NLO response 1.37 × AgGaS. It has the largest band gap among the noncentrosymmetric A-M-Se (A = alkali metal; M = Ga, In) compounds. The NLO properties' origin is explored via theoretical analysis. The success of NaGaSe contributes a practical case for exploring new NLO materials.