FIELD: optical products. SUBSTANCE: invention relates to terahertz (hereinafter – THz) materials specifically to THz crystals, from which windows, lenses, films and optical systems are made for operation in terahertz, millimeter, infrared and visible spectral ranges. The terahertz crystal, according to the invention, is made based on single-phase solid solutions of AgBr-AgI system, and it contains silver bromide and iodide at a certain ratio of ingredients. Crystals, according to the invention, have high transparency in a wide spectral range – in terahertz and millimeter – from 50 to 78%, in infrared – up to 78% and in visible – up to 65%, have a high degree of purity and can be obtained by low-cost technological methods. EFFECT: crystals are non-toxic so optical products made based on them will find wide application in medicine, pharmaceutics and other areas of the national economy. 1 cl, 3 ex.