Optical spectroscopy of solute lead in NaCl:Sr crystals

The optical spectroscopy (absorption and luminescence) of a small concentration of lead (∼10 ppm) incorporated into a NaCl:Sr crystal, containing a relatively higher concentration of Sr (∼350 ppm), has been investigated. For samples annealed at room temperature after quenching, two overlapping absorption bands at 255 and 260 nm grow at the expenses of the $A$ band typical of dissolved ${\mathrm{Pb}}^{2+}$. For high-temperature (150 and 300 °C) annealed samples, the 255- and 260-nm bands grow initially, saturate, and finally decrease for the benefit of another band at 249 nm, which becomes prominent after a long time. The same band is observed in as-grown samples. The luminescence emissions for the various bands have been determined. In the light of the available information, it has been concluded that the 249-nm band corresponds to ${\mathrm{Pb}}^{2+}$ incorporated into Sr${\mathrm{Cl}}_2$ precipitates, whereas the 255- and 260-nm bands should be associated to some intermediate phases, whose structure is not currently known.