Optical Studies on KBr:Tl and KCl-Br:Tl Mixed Crystals
Optical absorption spectra of KBr:Tl+ (0.0125 mol%) single crystals shows A, B and C bands around 258, 220 and 210 nm respectively. In KCl0.1Br0.9 :Tl+ (0.0125 mol%) mixed crystals exhibit slightly broadening of the A-band towards lower wavelength side. The broadening of the absorption spectra are suggested to be due to some complex Tl+ centers involving Br- and Cl- ions formed in the mixed crystals. When excited at A, B and C-bands of Tl+ ions, PL of KBr:Tl+ showed emission band around 320 with a prominent shoulder around 365 nm. In KCl0.1Br0.9 mixed crystals the shoulder around 365 nm is not prominent due to the perturbing influence of Cl- ions. Addition bands in the excitation spectra are attributed to the presence of Tl+ dimmers. PSL observed in X-ray irradiated crystals resembled their respective PL emissions indicating that PSL in them is due to Tl+ ions.
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