Cadmium sulfide

Overview
Cadmium sulfide is a chemical compound with the formula CdS. It exists in nature as two different minerals, greenockite and hawleyite.

Greenockite forms hexagonal crystals with the wurtzite structure. It has a yellowish colour with specific gravity of 4.7 and Mohs hardness of 3.8. Hawleyite has the sphalerite (zinc blende) structure.

Synthetic cadmium pigments based on cadmium sulfide are valued for their good thermal stability in many polymers, for example in engineering plastics. By adding selenium in its formula its possible to obtain colors ranging from a greenish yellow to red violet pigment. The weather resistance for this pigment is 8 in full tone, which means that it is a good pigment for UV.

Cadmium sulfide is a direct bandgap semiconductor with a bandgap of 2.42 eV. It has useful properties for optoelectronics, being used in both photosensitive and photovoltaic devices. One simple use is as a photoresistor whose electrical resistance changes with incident light levels.

Mixed with zinc sulfide, cadmium sulfide acts as a phosphor with long afterglow.

Cadmium sulfide was used as a pigment in paints as far back as 1819, although it wasn't big on any market until the mid-nineteenth century because of how rare the substance is. Most cadmium sulfide used in paints is manufactured in laboratories through chemical means in modern times.

Painters like Claude Monet liked this pigment because it had a nice, cool shade of yellow, good for outdoor-type paintings.