From Centrosymmetric Eu₂Ga₂S₅ to Noncentrosymmetric EuMg₆Ga₆S₁₆ via Introduction of Distorted MgS₆ Octahedron: Featuring Wide Bandgap and Nonlinear Optical Activity

Rare-earth chalcogenides have emerged as promising materials for infrared nonlinear optical (IR NLO) applications owing to their exceptional physicochemical properties. In this work, the introduction of distorted [MgS6] octahedra into the parent Eu2Ga2S5 induces a centrosymmetric to noncentrosymmetric structural transformation, leading to the successful synthesis of novel EuMg6Ga6S16 (EMGS). Its structure is composed of [EuS6] triangular prisms, [MgS6] octahedra, and [GaS4] tetrahedra, among which the [MgS6] octahedra show the largest distortion degree. EMGS exhibits a phase-matchable second-harmonic generation response, enhanced laser-induced damage threshold, and almost the widest optical band gap among Eu-based IR NLO chalcogenides. Besides, EMGS shows a green emission at 553 nm. Theoretical calculations indicate that the NLO response and band gap of EMGS are mainly contributed by the distorted [MgS6] units. This work enriches the chemical diversity of IR NLO Eu-based chalcogenides and provides an interesting case for designing Eu-based chalcogenides with wide optical band gaps.