ABSTRACT
This chapter explains fundamental optical properties and luminescence characteristics and mechanisms of this class of phosphors. IIb-VIb compounds crystallize either in the cubic zinc blende (ZB) structure or in the hexagonal wurtzite (W) structure; ZnO, CdS, and CdSe crystallize in the W structure, while ZnSe, ZnTe, and CdTe in the ZB structure. In IIb-VI compounds, the sublimation pressure is very high. As a result, the compounds, with the exception of the tellurides, do not melt at atmospheric pressure. In IIb-VIb compounds, the exciton structure is clearly observed at low temperature in absorption and reflection spectra near the fundamental absorption edge. ZnS type phosphors such as the green-emitting ZnS:Cu,Al and the blue-emitting ZnS:Ag,Cl are very important from a practical point of view, especially as phosphors for cathode-ray tubes. The chapter discusses nature of the electronic transitions responsible for the luminescence in ZnS phosphors was actively.
