The (Zn1–xCox)4B6O13 (x = 0, 0.375, 0.5, 0.75) solid solutions were prepared using solid-state synthesis. The borates crystallize in the cubic crystal system (I (Formula presented) 3m). According to the X-ray powder diffraction data, the unit cell parameter a slightly decreases with the increase in the x(Co2+) content. Crystal structure can be described as a sodalite cage composed of the [B24O48] clusters built from the vertex-sharing [BO4]5–tetrahedra with the [MO4]6–(M = Zn, Co) tetrahedra located inside the cage to form the [M4O13]18−supertetrahedron. The O(1) atom is coordinated by four M2+cations forming the isolated oxo-centered [OM4]6+tetrahedra. A thermal behavior of the solid solutions was investigated by in-situ powder XRD (103–573 K) and thermal analysis (303–1343 K). Melting temperature decreases from 1217 (x(Co2+) = 0) to 1176 K (x(Co2+) = 0.75). Low thermal expansion was observed in the range 103–573 K. The increase in the x(Co2+) content leads to an increase in values of average linear thermal expansion coefficient α from 2.4 (x(Co2+) = 0) to 6.7 × 10−6 K−1(x(Co2+) = 0.75). Thermal expansion coefficients were also calculated for the bond lengths, polyhedral volume and interpolyhedral angles. The increase in thermal expansion with both cationic substitution and temperature is attributed to a widening of angles between the cage-forming [BO4]5–tetrahedra and an elongation of the M2+–O bonds. With the increasing x(Co2+) content, a decrease in intensity of photoluminescence bands is observed, which is associated with concentration quenching. Increasing x(Co2+) content reduces the bandgap from 5.82 eV to 4.05 eV as evidenced by absorption spectroscopy positioning these solid solutions as promising wide-band semiconductors. © 2026 Elsevier Ltd and Techna Group S.r.l. All rights are reserved, including those for text and data mining, AI training, and similar technologies.