Emission properties of Ta-centres in KCl
Introduction
The electrolytic colouration of alkali halide crystals containing heavy metal ions such as Cu+ and Ag+ leads to the formation of negative metal ions such as Cu− and Ag− (Topa 1967; Topa et al., 1972; Tsuboi et al., 2000). When the KCl crystals with Pb2+ ions are electrolytically coloured using a pointed cathode and a flat anode, negative lead ions (such as Pb−) centres, called Ta-centres, are formed (Velicescu and Topa 1973; Topa et al., 1992).
This paper studies the spectroscopic properties of Ta-centres in electrolytically coloured KCl:Pb2+ crystal and KCl:Pb2+ crystals co-doped with and Rb+ ions. Special attention was paid to: (1) the near-infrared emission, and (2) the influence of F-centres as well as co-doped alkali ions and Rb+ on the Ta-centres.
Section snippets
Experimental details
Pure raw powder of KCl was heated in CCl4 in the melt in order to remove the OH− complexes. For crystal growth of doped KCl crystal, KCl powder containing salt was prepared, while for growth of co-doped crystal, KCl powder containing of NaCl, LiCl, or RbCl salt was prepared. Here doped crystal means KCl crystal doped with Pb2+ ions but without impurity alkali ions. Single crystals were grown by the Kyropoulos method in a dried nitrogen atmosphere.
The
Results and discussions
When electrolytically coloured co-doped and crystals were excited by the laser at , a broad emission band was observed at about for all crystals except KCl co-doped with Li+ ions. In the Li+-co-doped crystal, the peak was at about as shown in Fig. 1. The same emission spectrum was obtained by excitation with 266, 355, 366, 488.0 and laser lines. Unlike Na+ and locates at an off-centre position (Tsuboi et al., 2000),
Summary
Absorption bands are observed in electrolytically coloured KCl:Pb2+ crystals in the visible-UV region. Excitation into these bands gives rise to the same broad emission band, indicating that these bands are due to the same Ta-centre, related to Pb−. The electrolytically coloured KCl:Pb2+ crystals co-doped with Na+ and Rb+ ions show the same result, but the emission band of Li+-co-doped crystal is a slightly shifted to low energy because of the off-centred Li+ ions. It is observed that
Acknowledgements
The authors thank the CERES Program and the Romanian Academy for financial support.
References (6)
Electrolytical coloured Ag+ doped alkali halides
Rev. Roum. Phys
(1967)- et al.
Fotoluminiscentia T-tentrov b sciolocinih galoidnih K-kristallov
Izv. AN SSSR Sev. Fiz
(1972) - Topa, V., Briat, B., Apostol, E., 1992. Magnetic circular dichroism and optical study of new Pb− complex centres in...
Cited by (2)
New perturbed Pb<sup>-</sup>-aggregate centers in electrolytically colored KBr:Pb<sup>2+</sup>+(Ca, Ba) crystals
2007, Journal of LuminescenceOptical spectroscopy and thermoluminescence of electrolytically colored KCl:Tl<sup>+</sup> crystals
2008, Journal of Optoelectronics and Advanced Materials