EN
The absorption spectrum of Bi_{12}SiO_{20}:Cu is measured in the spectral region 0.195-2.95 eV. The validity of the Urbach rule (2.08-2.95 eV) has been also verified. The photochromic effect of these samples in far IR region is investigated. The energy level diagram of Cu^{3+} cations in Bi-octahedrons is presented.