A high-performance IR nonlinear optical material Sr3MnGe2S8 achieved via partial cation substitution-induced structural transformation

Abstract

The development of Mn-based infrared nonlinear optical (IR-NLO) materials that concurrently exhibit a large second-harmonic generation response (SHG > 1.0 × AgGaS₂) and a wide band gap (E_g > 3.0 eV) remains a formidable challenge. Herein, we demonstrate a partial cation substitution strategy to address this issue, successfully transforming centrosymmetric Sr₂GeS₄ into a novel non-centrosymmetric quaternary sulfide, Sr₃MnGe₂S₈. The compound features a three-dimensional framework constructed from corner-sharing [MnS₄] and [GeS₄] tetrahedra, with Sr²⁺ cations residing in the interstitial spaces. Sr₃MnGe₂S₈ achieves an outstanding balance of key IR-NLO properties: it shows a strong SHG response (2.4 × AgGaS₂ at 2050 nm), a high laser-induced damage threshold (13.4 × AgGaS₂), and a wide E_g of 3.06 eV—ranking it among the best-performing Mn-based chalcogenides. Theoretical calculations and structural analysis reveal that the excellent NLO performance originates from the synergistic effects between the two distinct types of functional units. This work provides a valuable paradigm for designing high-performance IR-NLO materials through rational structural transformation, highlighting the power of chemical substitution in overcoming property trade-offs.