A peculiar mechanism of light absorption and emission related to the 3d-electron states in iron group atoms occurs in the dilute magnetic semiconductors (DMSs) along with the conventional band-to-band mechanism. The light emission from 3d-levels is important for electroluminescence applications. We have studied DMS Cd_1-xMn_xTe and Cd_1-x-yMn_xMg_yTe wherein the bright 3d-luminescence band near 2 eV is observed for (x + y) > 0.4. A saturation of 3d-luminescence intensity J_L is found to occur at a low excitation level J_ex when only a minor portion of manganese ions is excited. The saturation of the 3d-luminescence is more readily achieved in Cd_1-xMn_xTe for x > 0.5 when the temperature rises from 4 up to 77 K. The energy position of 3d-luminescence band in Cd_1-x-yMn_xMg_yTe depends weakly on the Mn and Cd relative concentrations, the value of y being fixed, but it shifts significantly towards higher energy with increasing value of y. Thus the incorporation of Mg contributes strongly to the inhomogeneous broadening and suppresses a Frenkel exciton migration via Mn²⁺ ions. This result is consistent with the decrease of saturation for Cd_1-x-yMn_xMg_yTe as compared to Cd_1-xMn_xTe. The luminescence decay becomes faster with the increasing J_ex due to the initiation of the nonradiative relaxation. The temperature and concentration dependences of J_L point out the importance of energy transfer between Mn²⁺ ions. The luminescence decay becomes faster with the increasing J_ex due to the initiation of the nonradiative relaxation. It turns out that for Cd_0.6Mn_0.4Te wherein the 3d-luminescence excitation threshold coincides with band-to-band Wannier exciton energy, the dependence of the 3d-luminescence intensity upon J_ex shows a peculiarity.