Although the continuing research on blue thin film electroluminescence
has led to fairly stable and efficient Srg:Ce devices, there is still
a lack of fundamental knowledge about the origin of the remaining ins
tability. The purity and stability of both the SrS host semiconductor
and the Ce activator have been examined, in the starting materials as
well as in the evaporated thin films. It is found that the SrS host is
relatively inert, but that it is imperative to choose a moisture-inse
nsitive Ce-based activator.