Elsevier

Radiation Measurements

Volume 38, Issues 4–6, August–December 2004, Pages 731-734
Radiation Measurements

Emission properties of Ta-centres in KCl

https://doi.org/10.1016/j.radmeas.2004.01.021Get rights and content

Abstract

Electrolytic colouration at about 600°C and 350V/cm, for KCl crystal containing Pb2+ and for KCl:Pb2+ crystals co-doped with Li+,Na+ and Rb+ has been undertaken. Several absorption bands were observed in both doped and co-doped crystals in the visible-UV region. Excitation into these bands gives rise to the same 0.86eV emission band except for the Li+-co-doped crystal which gives rise to a 0.80eV emission band. These absorption bands are due to the same Ta-centre related to Pb. The observed infrared emission intensity of the crystal with F-centres is higher than of without F-centres.

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 Na+,Li+ 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 Na+,Li+ 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 0.018mol%PbCl2 salt was prepared, while for growth of co-doped crystal, KCl powder containing 0.93mol% of NaCl, 0.96mol% LiCl, or 0.5mol% 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 dopedKCl:Pb2+ crystals were excited by the 514.5nmAr+ laser at 296K, a broad emission band was observed at about 0.86eV(1440nm) for all crystals except KCl co-doped with Li+ ions. In the Li+-co-doped crystal, the peak was at about 0.80eV(1550nm) as shown in Fig. 1. The same emission spectrum was obtained by excitation with 266, 355, 366, 488.0 and 632.8nm laser lines. Unlike Na+ and Rb+,Li+ 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 0.86eV 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.

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