OPTICAL RECOMBINATION MECHANISMS IN EU2-DOPED CAS AND SRS THIN-FILMS()

Excitation and deexcitation mechanisms of Eu2+ emission in CaS:Eu and SrS:Eu thin films have been studied. The photoluminescence spectra and the luminescence decay kinetics were examined as function of the temp erature. It was found that both internal transitions within the Eu2+ i ons and resonant energy transfer between different Eu centers are resp onsible for the Eu2+ luminescence excitation in low temperatures. More over, at temperatures T> 100 K, electron transfer between different eu ropium ions over the conduction band (CB) of the host lattice influenc es efficiency of the emission. This is possible since the Eu ion can c hange its charge state from 3+ to 2+ by trapping a CB electron via the 4f(6)5d1 Eu2+ excited state.