ELECTROLUMINESCENCE AND PHOTOLUMINESCENCE OF CERIUM-ACTIVATED ALKALINE-EARTH THIOGALLATE THIN-FILMS AND DEVICES

Thin films of cerium-activated alkaline earth thiogallate were investi gated for the fabrication of blue-emitting thin-film electroluminescen t (TFEL) devices. The films were prepared by RF sputtering from target s with composition: M1-xGa2S4:Cex, where M = Ba, Ca, Sr, and 0.01 less -than-or-equal-to x less-than-or-equal-to 0.1. Photoluminescent (PL) e mission spectra showed matching peak wavelengths to those obtained fro m electroluminescent (EL) emission for each alkaline earth thiogallate film. The optimum cerium concentration for EL emission intensity for strontium and calcium thiogallate films was determined to be x = 0.04 and 0.06, respectively. The EL brightness measured for the calcium thi ogallate devices was almost twice that measured for the strontium thio gallate devices. This brightness variation, however, is due mainly to the difference in the lumen equivalent of the emission intensity. The cerium concentration dependence of the PL emission spectra of the thio gallate films is substantially decreased compared with the respective powder material suggesting inhomogeneous cerium incorporation in the f ilms.