Context <p>Halide perovskite materials have broad application prospects in fields, such as solar cells, sensors, and light-emitting diodes (LEDs). Employing the density-functional theory, this study explored the mechanical, electronic and optical properties of TlXY₃ (X = Mg, Ca, Sr, Ba; Y = Br, I). All cubic TlXY₃ crystals are mechanically, structurally and thermodynamically stable, as shown by the elastic constants and the Gold-Schmidt tolerance factor. Mechanical properties prove that they are all ductile compounds. TlXY₃ (X = Mg, Ca; Y = Br, I) are ionic bond materials, while TlXY₃ (X = Sr, Ba; Y = Br, I) are metallic bond compounds. The electronic properties indicate that TlXY₃ are all wide-bandgap semiconductor materials using HSE06 functional. The optical properties indicate that TlXY₃ all exhibit strong absorption and broad absorption peak within the UV spectral ranges and substantial transmission within the visible and infrared spectral ranges. Hence, these materials are well-suited as candidate materials for UV absorbers and ultraviolet-operating radiation detectors.</p> Methods <p>Density-functional theory (DFT) calculations were performed using CASTEP software. The GGA-PBE functional and the ultrasoft pseudopotential were employed to account for exchange–correlation. The elastic constants were determined via the stress–strain method. The electronic properties were calculated using the PBE and HSE06 hybrid functional, and the optical properties were calculated using the HSE06 hybrid functional.</p>