Optical absorption and luminescence study of color centers produced by γ-irradiated Sodium Chloride single crystals

Color center research in alkali halide crystals is receiving a fresh impetus in view of their application as color center lasers and information storage media. Among the family of alkali halides having the rock salt Fcc structure, Na Cl was the most favoured for experimental investigation in view of its nature and simply in coloration. Useful information on the optical characteristics of irradiated NaCl crystals is reported. Na Cl single crystals were γ-irradiated for doses varying 5 and 14 K Gy range at about 28 degree C. Studies of optical absorption and luminescence of the colored crystals have been done at 20, 77, and 300 K, using Cary 17 DX and modular photoluminescence setup with single beam spectrometer GCA(216-5), respectively. The crystal have been grown by Czochralski method. The absorption and luminescence spectrum are separated and show a large stokes shift without overlap which is suitable for laser applications. In this type of crystal, the shape of the optical absorption and luminescence bands are pekarian, with half width of approximately Δ ν 1000 cm-1. The result obtained shows that the half-width and the position of the F-band in the crystal are 0.287 eV and 2.796 eV at 77 K, and 0.478 eV and 2.674 eV at room temperature in the case of luminescence, the above parameter are 0.31 eV and 1.23 eV at 77 K and 0.389 eV and 1.121 eV at room temperature. (author)