INVESTIGATIONS OF THE INFLUENCE OF HALIDES ON THE PROPERTIES OF CEX(3)-DOPED (X=CL, F) STRONTIUM SULFIDE THIN-FILM ELECTROLUMINESCENCE DEVICES

Cerium activated strontium sulphide (SrS:Ce) phosphor layers for thin film electroluminescence (TFEL) devices have been prepared using a mul ti-source deposition method. CeCl3 has been used as dopant starting ma terial for reference SrS:Ce,Cl samples. Additionally, CeF3 has been em ployed in several cerium concentration series to study the influence o f the halides, The concentrations of cerium and of the halide in all l ayers have been determined by X-ray photoelectron spectroscopy (XPS). Cathodoluminescence (CL) and electroluminescence (EL) emission spectra of luminance-optimized phosphor films have been measured. Additionall y, the effect of the halide containing codopants LiCl and LiF on the e mission characteristics has been studied. The maximum EL luminances ha ve been found at cerium concentrations of 0.26-0.28 at%. The cerium to halide ratio has been determined to 1:1 for all doping and codoping e xperiments. CL spectra of the corresponding active layers yield the C. I.E.1931 colors yellowish green in standard SrS:Ce,Cl and bluish green in SrS:Ce,F phosphors. Moreover, codoping with LiCl resulted in no me ntionable spectral change, whereas the emission of SrS:Ce,Cl:LiF shift ed to green. The measured blue shifts have been attributed to the Neph elauxetic Effect.