Effects of Preparation and Operation Conditions on Electroluminescence Spectra of ZnS:TbF3 Film Structures

Among rare earth elements Tb is the most effective activator for ZnS thin-film electroluminescent structures (TFELS). It is usually introduced into the lattice as TbF3. The microstructure of the centers formed and their dependence on film preparation conditions have not yet been established. The model for the TbF3 molecular center has recently been reconsidered (see e3g. [1]). Essential information about the crystal field symmetry (CFS) around Tb ions can be obtained from the emission spectra. Conclusions about the excitation mechanism of electroluminescence (EL) can be obtained from the field dependence of the relative intensity of the 5D4–7Fj. and 5D3–7Fj bands. However ZnS:TbF3 TFELS spectra have been poorly investigated with most results reported at room temperature without allowance for interference effects. In this paper such spectra have been studied at temperatures in the range 4.2–300 K and the dependence on film preparation conditions and applied voltage are reported. EL spectra obtained are compared with Tb3+ emission spectra for materials which have different CFS and the results of the group-theory analysis of the level energy scheme are given. Center models as well as the origin of temperature and voltage effects on EL spectra are discussed.