In the present work, the spectral dependences of the efficiency of the formation of inherent electron color centers (c.c.) during the photoionization of such donors as Fe 2+ or Ce 3+ were investigated. The glass composition for this research was simple silicate glass of the composition (mol%) 22R 2O·3CaO·75SiO 2, where R = Li, Na, K. Admixtures of Tb 2O 3, CeO 2, and Eu 2O 3 were introduced into matrix. Glass samples of the two following types have been synthesized: (a) single activated glass samples with Fe 2+ or Ce 3+, and (b) double activated glass samples with the pairs Tb 3+ − Fe 3+, Tb 3+ − Eu 3+, and Ce 3+ − Ce 3+ − Fe 3+. The admixture concentration was ⪯ 0.5 mol%. The subject of research has been the spectra of initial, D( E), and induced, ΔD( E), absorption; the kinetics of the recombination donor afterglow; and the spectral dependences, η( E), of the efficiency of inherent electron c.c. formation in the case of admixture donor ionization. The absorption spectra of samples before and after irradiation were measured using standard spectrophotometers. By subtracting the non-irradiated glass sample spectra from the spectra measured after irradiation, the induced absorption spectra has been obtained. There exist two mechanisms of Fe 2+ or Ce 3+ photo-ionization in silicate glass, i.e. overbarrier and tunneling mechanisms. Thereby the overbarrier ionization takes place at E e > 5.6 eV for Fe 2+ and at E e > 3.9 eV for Ce 3+ while the tunneling ionization occurs at energies < 5.0 eV for Fe 2+ and & 3.4 eV for Ce 3+ In the intermediate ranges (5.6-5.2 eV for Fe 2+ and 3.9-3.4 eV for Ce 3+, mixed ionization takes place. Two independent methods were used to determine the average depth, E 0, of the ground state of impurity donors in the band-gap of our glasses. It proved equal to 5.0 eV for Tb 3+, 5.1 eV for Fe 2+, and 3.9 eV for Ce 3+ in sodium silicate glass. The concentration and type of the impurity acceptor do not affect E 0. The radius of electron trapping by Eu 3+ ions in sodium silicate glass is 4 to 5 times less than that for Fe 3+ ions.