Laser and thermal bleaching of colour centres in sodium borate glasses

The maximum of the additional absorption band in γ- or UV-irradiated sodium borate glasses shifts to higher energy when the low-energy side of the band is bleached by a helium-neon laser, Λ = 632.8 nm. Simultaneously the half-width of the additional absorption band decreases. This phenomenon is associated with the fact that because of structural disorder of glasses there is a distribution of ground-state energies of trapped electrons forming the light-sensitive absorption band. The distribution interval of the activation energy for trapped electrons is estimated using the decomposition of the initial thermal bleaching curves into components. For UV irradiated glasses it is aproximately 0.24 eV, and for γ-irradiated glasses only 0.12 eV. These values correlate with the relative shift maximum of the absorption band at laser bleaching. (author)