Optical ceramics of the TlCl0.74Br0.26 – AgI system are transparent in the range from 0.4 to 50.0 µm without absorption windows, which allows them to be used as transmission optics of the infrared range. In this work, the optical properties of four ceramic compositions 7, 14, 20 and 27 mol. % AgI in TlCl0.74Br0.26 were studied. The dispersion of the refractive index showed a normal dependence with an increase in the index real part from 2.173 to 2.348 to 2.236–2.419 with an increase in the proportion of AgI in TlCl0.74Br0.26 and a decrease in wavelength. The index imaginary part was 0,45∙10−4 – 13,1∙10−4 with low radiation attenuation in ceramics. The photoresistance of the samples showed the preservation of the transmission level at a wavelength of 10 µm or more. High radiation resistance was found under β-irradiation with doses up to 1000 kGy. The greatest losses reach 10 % in the entire transmission range. The formation of an antireflection coating on a ceramic sample of composition 20 mol. % AgI in TlCl0.74Br0.26 was detected. The obtained properties allow the use of ceramics of the TlCl0.74Br0.26 – AgI system under rough ionizing action in various wide-spectrum IR and THz devices.