Field-induced delocalization of Eu2+ and Ce3+ impurity levels in IIa–VIb semiconductors

Abstract We proposed a model for the light emission from II a –VI b semiconductors doped with Eu 2+ and Ce 3+ ion, considering the mixing interaction between the conduction electrons and the localized d electrons under the high-electric fields. Introducing the modified Anderson Hamiltonian and Wannier–Stark levels, we obtained the thermal Green's function and the self-energy for the localized electrons. Using asymptote of the Airy function we calculated the energy shift of the localized level and delocalization probability, and found that they depend strongly on the mixing interaction and the electric field intensity. Moreover, we estimated the electroluminescent relaxation time by using the delocalization probability and found, comparing the calculational relaxation time with the experimental one, that the excited levels of Eu 2+ and Ce 3+ ions in the CaS : Eu and SrS : Ce,Cl devices are placed below 0.15–0.4 eV from the bottom of the conduction band of the host materials and their mixing interaction with conduction electrons is expected to be 0.5–0.8 eV.