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

We proposed a model for the light emission from IIa-VIb semiconductors dope d with EU2 + and Ce3 + 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 lev els, we obtained the thermal Green's function and the self-energy for the l ocalized electrons. Using asymptote of the Airy function we calculated the energy shift of the localized level and delocalization probability, and fou nd that they depend strongly on the mixing interaction and the electric fie ld intensity. Moreover, we estimated the electroluminescent relaxation time by using the delocalization probability and found, comparing the calculati onal relaxation time with the experimental one, that the excited levels of Eu2 + and Ce3 + 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. (C) 2000 Elsevier Science B.V. All rights reserved.