Luminescence of CaS : Bi

Abstract

Luminescence of bismuth activated CaS, CaS:Bi, prepared in sodium polysulfide is studied. Excitation spectrum of CaS:Bi shows a band at 350 nm due to the recombination process between holes in Na-Ca(+)2+ and electrons in conduction bands, in addition to bands at 260 nm from band gap of CaS, and at 320 nm (S-1(0) --> P-1(1)) and at 420 nm (S-1(0) --> P-3(1)) from electronic energy transitions of Bi. Emission band at 450 nm is from P-3(1) --> S-1(0) transition of Bi3+, bands at 500 nm and 580 nm correspond to recombinations of electron donors (Bi-Ca(3+)2+ and V-S(2-)) with accepters (V-Ca(2+) and Na-Ca(+)2+). Emission band of P-3(1) --> S-1(0) transition is shifted to longer wavelength from CaS:Bi to BaS:Bi, due to the increase of the Stokes shift by the decrease of the crystal field parameter from CaS:Bi to BaS:Bi.