Alkali metal coactivators in SrS: Cu,F thin-film electroluminescent devices

A unique approach for obtaining bright and efficient saturated green phosph ors for alternating-current thin-film electroluminescent (ACTFEL) device ap plications is presented. The approach involves color-shifting blue SrS:Cu,F ACTFEL phosphors into the green region of the spectrum via the incorporati on of alkali metal ions into the SrS lattice. Alkali metals are incorporate d into SrS:Cu,F phosphors by using LiF, NaF, KF, RbF, or CsF coactivators. The best result to date is obtained by using a KF coactivator and results i n a saturated green brightness and efficiency of 52.7 cd/m(2) and 0.973 lm/ W (at a frequency of 60 Hz and an overvoltage of 40 V). In addition to prov iding a color shift, the alkali-metal fluorides improve the overall perform ance of the ACTFEL device by increasing the magnitude of the electric field and its uniformity across the phosphor through suppression of positive spa ce charge. (C) 1999 American Institute of Physics. [S0003-6951(99)04736-1].