Optical properties of crystalline materials based on AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems

For the development of optical technologies aimed at research, diagnostics and operation in a wide spectral range, the creation of new materials capable of being highly transparent and effective for transmitting electromagnetic waves in the visible, IR and THz regions is required. This article studies the properties of single crystals and two-phase ceramics based on solid solutions of the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems. The materials showed transparency in the range of 0.4–60.0 and 350–1500 μm (0.20–0.86 THz). With an increase in the proportion of thallium halides in the AgCl0.25Br0.75 solid solutions, a shift and the transmission spectrum broadening to longer wavelengths was observed. These effects are typical for compounds with both Fm3m and Pm3m type cubic crystal lattice. The refractive indices of the developed materials have normal wavelength dispersion and vary from 2.107 to 2.539 depending on the system and composition. The indicators for solid solutions with an intermediate composition of homogeneity regions lie within the values characteristic of boundary compositions. Based on this data a description of the index dependence by the Sellmeier equation, adapted by Fleming, was obtained. The refractive indices imaginary parts of all developed materials were 0.11*10−4–3.55*10−4, which was 2–4 times lower in comparison with other substances based on silver and thallium halides. The materials were characterized by a photostability improvement with an increase in the part of thallium halides in the solid solution, as well as with a growth in the amount of the orthorhombic phase in the case of two-phase ceramics. The materials showed low values of optical losses, as well as high functional properties. This makes single crystals and ceramics promising for transmission and fiber optics designed to operate in a wide spectral range.