Luminescence Centers of Ca(S:Se):Sn²⁺ Phosphors

Abstract

Emission, excitation and reflection spectra at various temperatures are studied. Under the C-band excitation, a simple emission band independent of the activator concentrations is observed for all the Ca(S:Se):Sn²⁺ phosphors. As the fraction of CaSe is increased, the band-peak (545 mμ for CaS:Sn²⁺ at 77 K) shifts constantly towards shorter wavelengths and finally reaches 518 mμ in CaSe:Sn²⁺ at 77K. In the excitation spectra, the curves characteristic of the Tl⁺-type ion center in the O_h crystal field can be obtained for all the Ca(S:Se):Sn²⁺ phosphors. The peaks of the C, B and A excitation bands are found at 311, 332 and 364 mμ for CaS:Sn²⁺, and at 327, 344 and 373 mμ for CaSe:Sn²⁺ at 77 K. For all the Ca(S:Se):Sn²⁺ phosphors, two additional excitation bands (409 and 448 mμ for CaSe:Sn at 77 K) are observed in the longer wavelength region of the A band at low temperatures.