In the present paper we have focus our study on relaxation of photodarkening in a-As₂S₃ doped with rare-earth ions (Dy³⁺, Pr³⁺, Nd³⁺). It was shown that the degree of photostructural transformation depends on the species and concentration of rare-earth ions. The relaxation process of photodarkening is described by a stretched exponential function with the dispersion parameter 0<α[removed]