Photoluminescence Spectra of Eu²⁺Centers in Ca(S, Se):Eu and Sr(S, Se):Eu

Abstract

Photoluminescence and excitation spectra are observed for Ca(S, Se):Eu 2+ and Sr(S, Se):Eu 2+ powder phosphors at various temperatures between 4.2 and 300 K. The emission band of Ca(S 1- x Se x ):Eu 2+ at 300 K shifts almost linearly with an increase in x , from 652 nm ( x =0) to 597 nm ( x =1). In Sr(S 1- x Se x ):Eu 2+ , 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:Eu 2+ , CaSe:Eu 2+ , SrS:Eu 2+ and SrSe:Eu 2+ . The excitation processes are attributed to two transitions; the intraionic 4 f 7 →4 f 6 5 d transition within Eu 2+ and the fundamental absorption by host crystal, followed by the transfer of the excitation energy to an unexcited Eu 2+ ion.