Lifetime spectroscopy of the chalcogenide systems Ga-Ge-S:Er³⁺ and Ga-Ge-S-Se:Er³⁺ has shown that the non-radiative energy transfer from rare-earth ions to the electronic states of the chalcogenide matrix is important. Numerical calculations of transition probabilities (W_R, W_mph, W_CR) allowed estimation of the probability of the energy transfer to the chalcogenide matrix. It was found that when the optical bandgap of the matrix approaches the Er³⁺ level, the probability of such energy transfer process will increase as long as a complete resonance is not achieved.