Radiation Measurements 38 (2004) 731 – 734 www.elsevier.com/locate/radmeas Emission properties of T a -centres in KCl V. Topa a , T. Tsuboi b , S. Polosan c ; ∗ a Center for Advanced Studies in Physics of the Romanian Academy, St 13 Septembrie., No 13, Bucharest, Romania b Faculty of Engineering, Kyoto Sangyo University, Kamigamo, Kita-ku, Kyoto 603-8555, Japan c National Institute of Materials Physics, P.O. Box MG-7, Bucharest R-76900, Romania Received 27 October 2003; received in revised form 6 January 2004; accepted 7 January 2004 Abstract Electrolytic colouration at about 600 ◦ C and 350 V= cm, for KCl crystal containing Pb 2+ and for KCl : Pb 2+ 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 0:86 eV emission band except for the Li + -co-doped crystal which gives rise to a 0:80 eV 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. c  2004 Elsevier Ltd. All rights reserved. Keywords: Emission spectra; Electrolytic coloring; Heavy metals negative ions; Ta -centres 1. Introduction The electrolytic colouration of alkali halide crystals con- taining 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 Pb 2+ ions are electrolytically coloured using a pointed cathode and a at 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 : Pb 2+ crystal and KCl : Pb 2+ crystals co-doped with Na + ; Li + and Rb + ions. Special attention was paid to: (1) the near-infrared emission, and (2) the inuence of F-centres as well as co-doped alkali ions Na + ; Li + and Rb + on the Ta -centres. 2. Experimental details Pure raw powder of KCl was heated in CCl4 in the melt in order to remove the OH - complexes. For ∗ Corresponding author. Optical and Spectroscopy, National Institute for Materials Physics, Fizicienilor St., no. 105 b BucharestMagurele 77900, Romania. Tel.: +40-214-930-195; fax: +40-2149-302-67. E-mail address: silv@alpha1.inm.ro (S. Polosan). crystal growth of doped KCl crystal, KCl powder contain- ing 0:018 mol% PbCl2 salt was prepared, while for growth of co-doped crystal, KCl powder containing 0:93 mol% of NaCl, 0:96 mol% LiCl, or 0:5 mol% RbCl salt was prepared. Here doped crystal means KCl crystal doped with Pb 2+ ions but without impurity alkali ions. Single crystals were grown by the Kyropoulos method in a dried nitrogen atmosphere. The electrolytic colouration was performed at about 600 ◦ C and 350 V= cm. The optical absorption and emis- sion measurements have been described previously (Tsuboi et al., 2002). The intensity of emission was detected us- ing a Ge or PbS photocell, and the emission spectra were recorded with an Advantest Q8381 a spectral analyzer. 3. Results and discussions When electrolytically coloured co-doped and doped KCl : Pb 2+ crystals were excited by the 514:5 nm Ar + laser at 296 K, a broad emission band was observed at about 0:86 eV (1440 nm) for all crystals except KCl co-doped with Li + ions. In the Li + -co-doped crystal, the peak was at about 0:80 eV (1550 nm) as shown in Fig. 1. The same emission spectrum was obtained by excitation with 266, 355, 366, 488.0 and 632:8 nm laser lines. Unlike Na + and Rb + ; Li + locates at an o-centre position (Tsuboi et al., 1350-4487/$ - see front matter c  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.01.021