EN
We have analyzed the Co influence on the absorption spectra of (80-x)Sb_2O_3-20Na_2O-xWO_3 glasses in the Urbach rule region at room temperature. We present the comparison between Co and WO_3 manifestation in the spectral region 2.64-3.14 eV. The spectral characteristics of "crystalline" and "glassy" Urbach's rule are also calculated.