CATHODOLUMINESCENT PROPERTIES AND ENERGY-TRANSFER IN RED CALCIUM SULFIDE PHOSPHORS (CASEU, MN)

Red and orange calcium sulfide phosphors (CaS:Eu and CaS:Mn) were prepared by the flux method. Eu2+ and Mn2+ show strong concentration quenching at 0.1 and 0.8% respectively. Use of the potassium polysulfide flux leads to efficient phosphors; their efficiency reaches 60 and 100%. of Y2O2S:Eu, respectively. Calcium sulfide codoped with Eu and Mn shows a strong increase of Eu2+ in addition to Mn2+ emission. The colour obtained varies between red and orange depending on the concentration rates of Mn and Eu. A luminous efficiency of about 86% was reached for CaS:Eu(0.08%), Mn(0.3%). The decay characteristics of Mn2+ in CaS:Mn, Eu show that the fast part depends on the Eu2+ content. On the other hand, the Eu2+ decay became slower in the presence of Mn2+. These observations support the resonant mechanism of the energy transfer from Mn2+ to Eu2+.