The phosphorescence of various solids

Ultra-violet radiation absorbed by a solid may be dissipated either as heat or as luminescence. If the electrons involved in the absorption transitions return to the ground state in a time not greater than 10-6 sec., the resulting emission is described as fluorescence. Delayed return is generally referred to as phosphorescence, and it is the chief object of this paper to describe some measurements of the decay law for various solids, together with some associated measurements of photoconductivity. A preliminary account of this work has already been published (Randall and Wilkins 1939).