A2Zn3P4S13 (A = Rb and Cs): First Infrared Nonlinear Optical Materials with Mixed Thiophosphate Functional Motifs PS4 and P2S6

Abstract

Two new IR NLO compounds, namely Rb₂Zn₃P₄S₁₃ (1) and Cs₂Zn₃P₄S₁₃ (2), have been obtained by introducing d¹⁰ closed-shell cations in an alkali-metal containing thiophosphate system. Compounds 1 and 2 are isostructural and feature a 3D [Zn₃P₄S₁₃] anionic framework. Both compounds exhibit moderate phase-matching SHG intensities at 1910 nm (0.1 × AGS for 1 and 2) and high LIDTs (6.1 × AGS for 1 and 5.2 × AGS for 2). They have wide transparent regions of 2.5–17.7 μm and 2.5–17.0 μm for 1 and 2, respectively, which cover the important far-IR atmospheric window of 3–5 and 8–14 μm for practical applications. Both compounds simultaneously contain two types of NLO-active thiophosphate units (PS₄ and P₂S₆) in their structures, which to the best of our knowledge, is unprecedented in known IR NLO thiophosphates. The NLO efficiencies of 1 and 2 are mainly due to the covalent [Zn₂P₂S₇]²⁻ framework, in which the contribution of P₂S₆ units is remarkably larger than that of the PS₄ units. This work sheds light on the design of promising IR NLO materials by mixing different thiophosphate functional motifs.