The Blue Luminescence of Zinc Sulfide

Abstract

It is shown that the ions Cl-, Br-, and I-play an essential part in the blue centers of ZnS.Ag, ZnS.Zn, and ZnS.Cu phosphors. The centers are assumed to be Ag+Cl -, and Cu+Cl -, respectively, (or the corresponding bromides and iodides), and to occupy normal zinc and sulfur sites in the zinc sulfide lattice. The spectral distribution of the fluorescence is the same for the centers containing chlorine or bromine ions; Ag, Zn, and Cu cause bands at slightly different wave lengths.A difference in peak positions for wurtzite and sphalerite is explained by the difference in separation between the upper occupied and the lower empty energy band of the base lattice.

Studies on a new method of preparation of zinc sulphide useful for luminescent phosphors

“…It is most significant from the figure giving diffuse reflectance spectra that of the four samples, only sample 4 (precipitated at a concentration of 5~o NaOH) has an absorption edge of 340 nm [15,17] (corresponding to a band gap of 3.636 eV). This coincides with the reported value of 341 nm (which corresponds to a band gap of 3.647 eV) for fi-ZnS [4,18,19]. The other samples, viz.…”

“…In the band model of zinc sulphide, Zn + ions are known to be at the foot of the conduction band and the S 2-ions at the top of the valence band [20,21,22]. The accepted band gap is 3.64 eV [4,18,19] for /~-ZnS. It is necessary to explain why the three zinc sulphide samples precipitated at concentrations of 10~, 15~ and 20~o (w/v) of sodium hydroxide have an identical band gap smaller than the accepted value of 3.64 eV.…”

“…The first four zinc sulphide samples were white in colour whereas the last one containing zinc oxide was yellow in colour. It is reported in the literature [4,15] that zinc sulphide containing predominantly zinc oxide is coloured yellow.…”

“…Extensive literature [1][2][3][4][5] exists on the synthesis of zinc sulphide phosphors. All the methods are based on the precipitation of zinc sulphide by hydrogen sulphide under varying conditions of pH, anions, etc.…”

X-ray studies and luminescence of ZnS-phosphor doped with silver and cobalt

“…On the other hand, an excess 2860 of acceptor ions increased the intensity of the first band. This fact leads to the assumption that the blue band is not due to an association between the activator and the coactivator ions [16].…”