The Formation of Eu[sup 2+] Clusters in Saturated Red Ca[sub 0.5]Sr[sub 0.5]S:Eu Electroluminescent Devices

Abstract

A high-luminance and high-color-purity inorganic phosphor Ca 0.5 Sr 0.5 S:Eu has been developed for the red component in ac thin-film electroluminescent devices using electron-beam evaporation. The influence of the Eu concentration on the luminescence and response characteristic of the Ca 0.5 Sr 0.5 S:Eu devices was studied. A high Eu concentration causes not only concentration quenching of photoluminescence and electroluminescence (EL) emission, but also increases the light-emitting response time of the Ca 0.5 Sr 0.5 S:Eu EL devices upon the application of an electric field. Decay characteristics of the Ca 0.5 Sr 0.5 S:Eu thin films, point out the creation of nonradiative decay channels due to the formation the Eu 2+ clusters at high Eu concentrations. The slow light-emitting response in Ca 0.5 Sr 0.5 :Eu EL devices was attributed to the presence of traps generated by these Eu 2+ clusters. To understand the nature of these traps, the frequency and temperature dependence of the response time was studied. © 2005 The Electrochemical Society. All rights reserved.