Electroluminescence and Photoluminescence in Eu-Doped SrS Thin-Films

The electroluminescence (EL) and photoluminescence (PL) characteristics of SrS:Eu, F thin-films have been studied. It is found that valence of the Eu luminescent centers is affected by the presence of F - ions. At lower Eu concentration less than 0.3 mol%, Eu 2+ centers exist, but at higher concentration over 0.6 mol%, both Eu 2+ and Eu 3+ centers coexist in the films. The Eu 2+ centers are efficient for both EL and PL. The excitation process of Eu 2+ centers is attributable to the energy transfer from the SrS lattice to Eu 2+ centers. On the contrary, Eu 3+ centers are efficient for EL only through the direct impact excitation by hot electrons.