Luminescence of CsCl : Tl Crystal under Synchrotron Excitation

Abstract

PACS: 71.55.Ht; 78.47.þp; 78.55.Fv For the first time, time-resolved emission and excitation spectra, as well as decay kinetics of luminescence of CsCl : Tl single crystals have been measured at 10 K under excitation in the 4-20 eV energy range. The results obtained confirm the earlier conclusion that the emission spectrum of the main thallium centres consists of five bands arising from the trigonal (3.88 eV) and tetragonal (3.65 eV) minima of the Tl þ triplet relaxed excited state and from the on-centre (4.56 eV), weak off-centre (%3.0 eV), and strong off-centre (2.55 eV) configurations of an exciton localized near the Tl þ ion. The origin of the excitation bands located in the 6.0-7.8 eV energy range has been discussed. The classification of various exciton emissions in CsCl crystals with respect to the lattice relaxation performed with the use of the Kan'no method has been considered. The conclusion has been made that the on-centre self-trapped exciton emission band of CsCl should be located at (5.9 AE 0.3) eV.

Luminescence of CsBr:Tl crystals under synchrotron excitation

“…However, the comparison with Ref. [6] allows to conclude that in CsBr:Tl the energy transfer efficiency is larger than in CsCl:Tl. For the high-energy group of excitation bands in 5.3-6.8 eV range the SC dominates under excitation with E exc 46:0 eV.…”

“…To confirm these conclusions and to obtain more information on the origin of the high-energy absorption (excitation) bands of Tl + -doped caesium halides, it is of interest to compare characteristics obtained in [6] for CsCl:Tl crystals with those of CsBr:Tl crystals.…”

“…The experiments were carried out at 9 K under excitation with synchrotron radiation at the SUPERLUMI station (HASYLAB, Hamburg) using the subnanosecond time-resolved spectroscopy technique (for more details see Ref [6]). The pulse duration and repetition interval of the synchrotron radiation light were 180 ps and 500 ns, respectively.…”

“…Like in CsCl:Tl [6], the positions of the highenergy bands in the excitation spectra, measured for the triplet ultraviolet emission of Tl + and the visible localized exciton emission, do not coincide (Fig. 6, compare curves 1, 2 and 3, 4).…”

“…Indeed, the study of CsCl:Tl crystals under synchrotron excitation, carried out by us in Ref. [6], allowed to conclude that besides the lowest-energy A band of Tl + ions and the charge-transfer bands, also B and C bands, arising from the transitions to the higherenergy excited states of a Tl + ion, and D bands, attributed to the exciton transition perturbed by a Tl + ion, are present in the absorption spectrum of CsCl:Tl. At 10 K the A band is peaking at 5.17 eV while the strongly overlapped charge-transfer bands and the B, C and D bands are located in the 6.0-7.8 eV energy range.…”