Chalcogenide single crystals from the hypothio(seleno)diphosphate family are exceptional materials that possess a combination of semiconducting, ferroelectric, and nonlinear optical properties. In this project, we will obtain new fundamental data on the parameters of this attractive class of 3D and 2D layered chalcogenide materials. This is especially noteworthy in the broadband THz range, where reliable experimental data are currently almost absent. We further expect the first demonstrations of applications in the field of THz photonics based on this type of material.