Calcium Selenide, CaSe

Selenium will unite directly with calcium at red heat to form the Calcium Selenide, CaSe. The heat of formation is 77.06 Cal. It can be prepared by the reduction of calcium selenate at 400° C. by hydrogen, by heating selenium with lime when a black mixture of selenide and selenite is obtained, or by precipitation of a soluble calcium salt by potassium selenide.

Calcium selenide is a white substance which becomes red on exposure to air owing to the liberation of selenium by the action of carbon dioxide. It is soluble in dilute acids and is decomposed by water. It can be obtained in the phosphorescent state by admixture with a suitable phosphorogen, copper, bismuth, manganese, nickel, antimony, etc. The intensity and duration of the phosphorescence is much smaller than in the case of the sulphides. The position of brightest phosphorescence in the spectrum is at a longer wave-length than in either the sulphur or oxygen compounds, and the upper wave-length above which the selenides are inactive is, in general, lower than for the corresponding sulphides.