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 (1S0 → 1P1) and at 420 nm (1S0 → 3P1) from electronic energy transitions of Bi. Emission band at 450 nm is from 3P1 → 1S0 transition of Bi3+, bands at 500 nm and 580 nm correspond to recombinations of electron donors (Bi3+(Ca)2+ and V(s)2-) with acceptors (V(Ca)2+ and Na+(Ca)2+). Emission band of 3P1 → 1S0 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.