FIELD: terahertz materials. SUBSTANCE: invention relates to a new halide crystalline class of terahertz (THz) materials based on solid solutions of monovalent thallium and silver. A terahertz crystal of the TlBr0.46I0.54 - AgI system includes a solid solution of TlBr0.46I0.54 and silver halide, while it is based on a solid solution and additionally contains silver iodide in the following ratio of components: solid solution TlBr0.46I0.54 - 98, 0-82.0 mol.%; silver iodide - 2.0-18.0 mol.%. EFFECT: invention provides TlBr0.46I0.54- AgI, photo and radiation-resistant, non-hygroscopic and plastic, highly industrial in a terarier range from 0.1 to 30.0 THz (from 3000 to 10 μm), as well as in visible and infrared, as well as in visible and infrared; the areas of without absorption windows from 0.5 to 60.0 microns, which opens wide areas of application as optical products and fibers for teraring technologies, photonics, laser and IR fiber optics. 1 cl, 1 dwg, 3 ex.