PHOTOLUMINESCENCE SPECTRA OF EU2+ CENTERS IN CA(S,SE)EU AND SR(S,SE)EU

Photoluminescence and excitation spectra are observed for Ca(S, Se):Eu2+ and Sr(S, Se):Eu2+ powder phosphors at various temperatures between 4.2 and 300 K. The emission band of Ca(S1-xSex):Eu2+ at 300 K shifts almost linearly with an increase in x, from 652 nm (x=0) to 597 nm (x=1). In Sr(S1-xSex):Eu2+, the emission band shifts also linearly from 620 nm (x=0) to 571 nm (x=1). At low temperatures, vibronic structures on emission bands are observed for CaS:Eu2+, CaSe:Eu2+, SrS:Eu2+ SrSe:Eu2+. The excitation processes are attributed to two transitions; the intraionic 4f(7)-->4f(6)5d transition within Eu2+ and the fundamental absorption by host crystal, followed by the transfer of the excitation energy to an unexcited Eu2+ ion.