Mechanisms of the formation of intrinsic and impurity color centers in sodium silicate glasses with two activators

A study was made on mechanisms of formation of intrinsic and impurity color centers in sodium silicate glasses of 22Na2O·3CaO·75SiO2 (mol %) composition, activated by Tb3+ - Eu3+ under UV irradiation. Electron color centers form during overbarrier or tunnel donor ionization. Overbarrier mechanism of ionization is realized at Ee>Eb, and tunnel one - at Ee<Eb. This dictates the spectral dependence of ionization efficiency of donor impurity (Ee -energy of exciting light quanta; Eb - depth of occurence of the basic donor state)