THE INFLUENCE OF SE-COEVAPORATION ON THE EMISSION-SPECTRA OF CAS-EU AND SRS-CE THIN-FILM ELECTROLUMINESCENT DEVICES

In order to reduce the number of sulphur vacancies in evaporated CaS:E u and SrS:Ce electroluminescent thin films, Se-coevaporation can be pe rformed. This process not only improves the brightness of the devices, but also induces considerable changes in the emission spectra. The sh ift of the electroluminescent spectra upon coevaporation was checked a gainst semi-empirical molecular cluster energy calculations. In the ca se of SrS:Ce, these spectral changes are seen to be entirely due to th e effect of electron-phonon interactions, while for CaS:Eu, only cryst al field effects play a role.