Exciton 4.29 and 3.65 eV luminescence in CsI:Tl and CsI:Pb

The 4.29 and 3.65 eV emission of CsI:Pb crystals has been studied at 4.2 - 300 K under excitation in the exciton as well as in the lead-induced absorption bands. The results have been compared with those obtained for the corresponding emission of CsI:Tl as well as for the emission of the on-centre and the off-centre self-trapped exciton in a pure CsI crystal. It has been found that, unlike the case in CsI:Tl, in CsI:Pb the 4.29 and 3.65 eV emission is excited not only in the exciton bands but also in the absorption bands of electron impurity centres optically created at 4.2 K together with the centres by photons of 5.1 - 4.0 eV energy. In the latter case this emission is of nature. The optical creation of the centres has been confirmed by luminescence polarization and ESR spectrum measurements.