The up-conversion fluorescence excited with 813 and 1550 nm light is investigated in glasses of the Ga₂S₃-GeS₂-Er₂S₃ system. The influence of the glassy matrix composition and Er concentration on the luminescence and absorption spectra is studied. Increasing the Ga content relative to Ge decreases the erbium concentration quenching effect. The efficiency of up-conversion fluorescence has a strong dependence on thermal history of the sample. Annealing of the glasses and decreasing the synthesis temperature increase the luminescence intensity.