Two thiophosphates, KInP
2S
7 and KCrP
2S
7, were structurally characterized without investigating any optical properties. Herein in this work, KInP
2S
7 and KCrP
2S
7 were revisited to investigate their optical and magnetic properties, respectively. Pure polycrystalline samples and crystals of KInP
2S
7 and KCrP
2S
7 were grown by high temperature solid state reactions, where mm-sized crystals of KCrP
2S
7 were collected. KCrP
2S
7 is isostructural to KInP
2S
7, which features a layered structure. KInP
2S
7 and KCrP
2S
7 possess close relationship to the layered thiophosphate M
2P
2S
6 (M = Fe, Co, Zn, etc.). The bonding pictures of KInP
2S
7 were studied using the electron localization function (ELF) coupled with crystal orbital Hamilton population (COHP) calculations. The intrinsically distorted [PS
4] tetrahedra and [InS
6] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. Electronic structure analysis confirmed that the optical properties of KInP
2S
7 are mainly contributed to by [PS
4] tetrahedra together with small amounts of the contributions coming from [InS
6] octahedra. Magnetic measurement on mm-sized crystals of KCrP
2S
7 verified that there is an antiferromagnetic transition around 21 K, and the Cr atoms are trivalent. KInP
2S
7 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. KInP
2S
7 is not a type-I phase-matching material and exhibits moderate second harmonic generation (SHG) response (0.51 × AgGaS
2, sample of particle size of 100 µm). The laser damage threshold (LDT) of KInP
2S
7 is very high of 5.2 × AgGaS
2. Bandgap engineering were undergone to enhance the SHG response of KInP
2S
7.
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