Peculiarities of the triplet relaxed excited-state structure and luminescence of a CsI:Tl crystal

Nagirnyi, V. and Stolovich, A. and Zazubovich, S. and Zepelin, Viktor and Mihokova, E. and Nikl, M. and Pazzi, G. P. and Salvini, L. (1995) Peculiarities of the triplet relaxed excited-state structure and luminescence of a CsI:Tl crystal. Journal of Physics: Condensed Matter, 7 (18). pp. 3637-3653. ISSN 0953-8984

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Four emission bands, all belonging to the main thallium centres, have been detected in CsI:Tl, and their spectral, polarization and kinetic characteristics have been studied at 0.35-320 K. A new model is proposed for the excited states responsible for the luminescence of thallium-doped caesium iodide. In this model, the main thallium centre is considered as a cluster consisting of a Tl+ ion and at least 12 I- and 11 Cs+ ions. Two weak ultraviolet emission bands of CsI:TI (3,31 and 3.09 eV) are ascribed to electronic transitions from trigonal and tetragonal Jahn-Teller minima of the tripler relaxed excited state, whose structure is similar to that of Tl+ centres in Fee alkali halides. Two intense visible bands (2.55 and 2.25 eV) are assumed to arise from two different ('weak' and 'strong') off-centre configurations of a self-trapped exciton perturbed by the Tl+ ion. The minima responsible for all the emission bands are located on the same adiabatic potential energy surface. The excitonic-like nature of visible emission could explain the high scintillation efficiency of CsI:Tl.

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Journal of Physics: Condensed Matter
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03 Feb 2009 14:27
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17 Sep 2023 00:28