Negatively charged Pb− ion produced by electrolytical colouration of KCl crystals containing Li+, Na+ and Rb+ ions

Electrolytic colouration has been undertaken for not only a KCl crystal containing Pb2+ ions but also KCl crystals containing alkali impurity ions (Li+, Na+ and Rb+) besides Pb2 + ions. Absorption spectra of these electrolytically coloured crystals have been studied, together with the emission spectra. Similar spectra were observed among these crystals. Eight weak absorption bands are observed in the 290–700 nm region, while five intense bands are observed in the 200–290 nm region. It is suggested that these bands arise from Pb− ions with tetragonal crystal field symmetry. The energy-level assignment for these absorption bands is made using the energy-level diagram of the isoelectronic Bi0 atom with C4v crystal field symmetry. It is suggested that an off-centre position effect of the Li+ ion is observed in the KCl crystal codoped with Li+ ions. Broad emission bands at 1530 and 1580 nm have been observed in electrolytically coloured KCl containing Pb2 + ions and KCl containing Li+ and Pb2 + ions, respectively.