Colour Centres in Ruby Crystals

An investigation is made of the absorption spectra, the spectral dependence of the luminescence quantum output, glow curves, and the radiation spectra of the glow curves of ruby crystals. These crystals are coloured by intense light flashes or by γ‐rays from Co60. It is found that the absorption is greater in coloured crystals while the luminescence quantum output is smaller. The thermal decoloration of crystals is accompanied by a luminescence in the R‐line region. A decrease in the Cr3+ ion concentration is detected in coloured crystals by ESR measurements. The similarity of all the characteristics obtained allows a conclusion about the identity of the colour centres arising under optical and γ‐irradiation of the crystals. The results obtained here and published data suggest that Cr2+ and Cr4+ act as colour centres, and that their formation under optical coloration is duo to Cr3+ ion ionization via a two‐step process. It is shown that the gradual increase of the ruby generation threshold observed experimentally, which gives laser operation, is due to the formation of colour centres which cause a parasitic absorption of the pumping light. [Russian Text Ignored].