where Io and I are the intensity of the incident and transmitted light,
respectively, and d is the sample thickness in cm. Fig. 3 shows the
optical absorption spectra of the investigated glassy samples as aaw
function of the wavelength. The spectra feature two kinds of
absorption bands, one for the spin-allowed d-d transitions of the
electrons belonging to chromium ions, whereas the other is attributed
to absorption by an electronic transition through the energy
band gap.