The development of optical materials, that are transparent from the visible to the far IR without absorption windows, including fiber optics materials, continues to be an urgent scientific problem, which is associated with high prospects for their application in wide-spectrum systems, IR and THz technology. This article is devoted to the development of materials based on the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems from constructing phase diagrams to synthesis of single crystals and optical ceramics and their transmission properties investigation. According to the results of studying the phase diagram of the AgCl0.25Br0.75 – TlCl0.74Br0.26 system, homogeneity regions of 0–7 mol. % and 95–100 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75, in which there are single-phase solid solutions with the structure Fm3m and Pm3 m, respectively, were obtained. In this diagram, regions of heterogeneity with a composition of 7–79 mol. % and 79–95 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 and a mixture of two phases in the first region Fm3m and R-3, and in the second region Pm3 m and R-3 were found. Within the AgCl0.25Br0.75 – TlBr0.46I0.54 system's phase diagram, homogeneity regions with compositions of 0–15 mol. % and 92–100 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 and similar structures Fm3m and Pm3 m, respectively, were determined. This system also contains regions of heterogeneity with compositions of 15–36 mol. %. and 69–92 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 with phase composition Fm3m and R-3, and Pm3 m and R-3. In each system, compositions were selected from the homogeneity and heterogeneity regions, and samples of single crystals and two-phase ceramics were synthesized. For the AgCl0.25Br0.75 – TlCl0.74Br0.26 system, a single crystal with a composition of 3 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 and two-phase ceramics of 7, 31, 86, 92 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 were obtained. Single crystals 3, 6, 9, 92 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 and ceramics 32, 76 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 were synthesized in AgCl0.25Br0.75 – TlBr0.46I0.54 system. The samples are 35 ± 5 mm high and 10 ± 0.1 mm in diameter, and their color varies from yellow to orange depending on the composition. The transmittance ranges of all synthesized samples were investigated. The study was carried out on polycrystalline plates with a diameter of 15 ± 5 mm, thickness of 400 ± 5 μm, and surface roughness Ra = 0.2 μm. The crystallite size of the alloying phase R-3 in the optical ceramics was less than 100 nm. For AgCl0.25Br0.75 – TlCl0.74Br0.26 system materials, the transmission spectra covered the region from 0.4 to 55.0 μm. Materials based on the AgCl0.25Br0.75 – TlBr0.46I0.54 system showed transmission in the wavelength range of 0.49–60.0 μm. All materials are transparent in the wide region without absorption windows with a transparency level up to 79%. Thus, new optical materials based on the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems have been developed, which have a wide transmission range from the visible to the IR. This opens broad prospects for their use as an optical material for wide-spectrum devices, as well as IR fiber optics.