Cerium sesquisulfide

Rare earth sesquisulfides exist in different allotropic forms (Figure 4-1). Cerium sesquisulfide is known to exist in 3 different allotropic forms a, (3, and y, all stable at different temperatures and exhibiting different colors (Table 4-2). 

Further research in this field is under way to extend the color range to yellow. Because of the limitations of the y-Ce2S3 doping approach, other systems than cerium sesquisulfides are under study. Sm2S3 appears to be a good candidate . ... 

Rhodia has now developed and commercialized a special process to produce rare earth sesquisulfides, notably cerium sesquisulfides with the adequate purity and size necessary for pigment application. 

Rare earth elements and sulfur combine to form a wide range of compounds as sulfides or oxysulfides Among them, sesquisulfides appeared to have the best potential as far as color is concerned (Table 4—1). We gave most of our attention to cerium sulfide, which was the most promising in terms of color intensity and purity. 

The transformation of the cerium precursor into the colored sesquisulfide is carried out at high temperatures (between 700 and 1100 C) in a sulfurizing atmosphere. The resulting colored sesquisulfide is then cooled to room temperature. 

---