ABSTRACT
Phosphors based on alkaline earth chalcogenides, mostly sulfides or selenides, are one of the oldest classes of phosphors. Even with their long history, progress in understanding the fundamental physical properties for these phosphors has been quite slow. There are good reasons for this: these materials are hygroscopic and produce toxic H2S or H2Se when placed in contact with moisture. The compounds in the NaCl-type structure can form solid solutions in a wide range of composition. As a consequence, the emission color can be varied by changing the host composition as well as the activator species and concentration. Application of CaS phosphors applied to cathode ray tubes (CRTs) have attracted attention because of their high efficiency and diversity in emission colors. The preparation of sulfide phosphors can be classified into two methods; one entails the sulfurization of alkaline earth oxides or carbonates and the other involves the reduction of sulfates.
