Source : Webster's Revised Unabridged Dictionary (1913)

Phosphorescent \Phos`phor*es"cent\, a. [Cf. F. phosphorescent.]
   Shining with a phosphoric light; luminous without sensible
   heat. -- n. A phosphorescent substance.

Source : WordNet®

phosphorescent
     adj : emitting light without appreciable heat as by slow oxidation
           of phosphorous; "the phosphorescent glow of decaying
           wood"