[en] We report photo-induced time-dependent photoluminescence (PL) from Ge-S glass that shows not only known PL fatigue but also a PL recovery phenomenon - observed under prolonged irradiation by the excitation light, even after PL fatigue - in Ge_1-xS_x glasses (0.67 ≤ x ≤ 0.90). The two phenomena have different time constants. Also, the fatigue process depends strongly on glass composition, excitation energy and excitation intensity, while the recovery process depends clearly only on excitation intensity. We propose a simplified functional form to describe the time dependence that is based on a model in which non-radiative recombination centres - created by the photo-excitation of the PL centres - revert to radiative centres through thermal reaction. The proposed function reproduces the experimental data for all irradiation time domains