Synthesis of chiral high-entropy sulfides for non-linear optical applications

Abstract

Non-centrosymmetric semiconductors may exhibit non-linear optical (NLO) properties. For application-relevant materials, a careful balance of high second-harmonic generation (SHG) and high laser damage threshold (LDT) as well as phase-matchability are required. We have previously identified (A)₂Cu₂Ge₂S₁₄ (A = Y, La, Sm, and Gd) phases as promising NLO materials. Here, we developed a synthetic method to produce solid solution and high-entropy sulfides containing up to 9 elements. We report the synthesis, crystal structure, and NLO properties for solid solutions and high-entropy multi-metallic materials (HEMs) of the type (A)₆(TM)_xGe₂S₁₄ (A = La, Sm, Gd, mixture of (Y + La + Ce + Sm + Gd); TM = Mn, Cu; 1 ≤ x ≤ 2). In this work, we establish that nearly all phases are phase matchable and the HEA composition with Cu possesses a SHG signal enhancement of 1.5× as compared to the AgGaS₂ (AGS) standard for the largest particle size, as well as a LDT value of 2.8× of AGS.