The optical properties of the chromium doped spinel type semiconductor α-ZnAl₂S₄ have been examined over the temperature range 2-540 K. The intrinsic photoluminescence (PL) showed an intense ultraviolet peak at 381 nm at 296 K. From extrinsic absorption and emission spectra the transitions between the ground state ⁴A_2g and the excited levels ²E_g, ²T_1g, ²T_2g, ⁴T_2g, and ⁴T_1g of Cr³⁺ ions were observed. A fit of the measured temperature dependence of the PL decay, using a four level model, yielded the lifetimes of the ²E_g, ²T_1g, and ⁴T_2g levels and the energy gaps between the ²E_g-²T_1g and ²E_g-⁴T_2g states which were found to be very close to the values obtained from steady-state measurements. A configurational coordinate diagram for Cr³⁺ ions in a α-ZnAl₂S₄:Cr spinel host has been constructed. Optical gain measurements at 198, 298, and 380 K displayed two separate spectral regions associated to the Cr³⁺ ions and possibly Cr⁴⁺ impurity centers. Gain values of up to 25 cm^-1 at 198 K were obtained