Zero-Phonon Transition and Spectral Hole Burning of Colour Centers in Doped Lithium Fluoride Crystals Bombarded by Electrons

Two zero-phonon lines with wide linewidth on R^-₁ and unknown colour centers have been observed in the magnesium-doped lithium fluoride crystals coloured by electron beam bombardment at 200K in the measured temperature range of 10 - 77K. The R^-₁ zero-phonon line can be nearly completely bleached using the normal spectrophotometer light at 10 K. An obvious spectral burning hole in the absorption profile of the R^-₁ zero-phonon line of colour centers in the coloured lithium fluoride crystals has been obtained by using the spectrophotometer light adjusted to narrower bandwidth at 10K. The optical bleaching of the zero-phonon line can be partially recovered by annealing the crystals to room temperature for a short time period or irradiating the crystals with ultraviolet light at above 40K, and nearly complete restoration can be obtained after the ultraviolet light irradiation and storage in the dark for a long time at room temperature.