The mother material CuIr₂S₄ of the thiospinel system Cu_1-xZn_xIr₂S₄ undergoes a temperature-induced metal--insulator (MI) transition. We report the temperature dependence of the optical reflection spectra of Cu_1-xZn_xIr₂S₄ (x\le 0.5) at the temperatures of 8--300 K in the energy regions of 0.005--30 eV in order to study the change in the electronic structure due to the Zn substitution for Cu. Zn substitution induced mainly the splitting of the hybridization band between the Ir-5d(t_2g) and S-3p states crossing the E_F. Obtained optical conductivity (\sigma ) spectrum is discussed in relation to the change in the electronic structure close to the E_F.

PACS numbers: 71.30.+h, 78.40.Kc