Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7

Abstract

Two thiophosphates, KInP2S7 and KCrP2S7, were structurally characterized without investigating any optical properties. Herein in this work, KInP2S7 and KCrP2S7 were revisited to investigate their optical and magnetic properties, respectively. Pure polycrystalline samples and crystals of KInP2S7 and KCrP2S7 were grown by high temperature solid state reactions, where mm-sized crystals of KCrP2S7 were collected. KCrP2S7 is isostructural to KInP2S7, which features a layered structure. KInP2S7 and KCrP2S7 possess close relationship to the layered thiophosphate M2P2S6 (M = Fe, Co, Zn, etc.). The bonding pictures of KInP2S7 were studied using the electron localization function (ELF) coupled with crystal orbital Hamilton population (COHP) calculations. The intrinsically distorted [PS4] tetrahedra and [InS6] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. Electronic structure analysis confirmed that the optical properties of KInP2S7 are mainly contributed to by [PS4] tetrahedra together with small amounts of the contributions coming from [InS6] octahedra. Magnetic measurement on mm-sized crystals of KCrP2S7 verified that there is an antiferromagnetic transition around 21 K, and the Cr atoms are trivalent. KInP2S7 is predicated to be an indirect bandgap semiconductor of 2.38 eV, which is confirmed by the UV-Vis measurement of 2.4(1) eV. KInP2S7 is not a type-I phase-matching material and exhibits moderate second harmonic generation (SHG) response (0.51 × AgGaS2, sample of particle size of 100 µm). The laser damage threshold (LDT) of KInP2S7 is very high of 5.2 × AgGaS2. Bandgap engineering were undergone to enhance the SHG response of KInP2S7.