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

Abstract

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.