Phosphorescence

Phosphorescence is a type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with 'forbidden' energy state transitions in quantum mechanics. As these transitions occur very slowly in certain materials, absorbed radiation is re-emitted at a lower intensity for up to several hours after the original excitation.Left: zinc sulfideRight: strontium aluminatePigments in the darkPigments in the dark after 4 minPhosphorescent pigment red (calcium sulfide)Phosphorescent pigment red in the darkPhosphorescent pigment blue (alkaline earth metal silicate )Phosphorescent pigment blue in the dark Phosphorescence is a type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs. The slower time scales of the re-emission are associated with 'forbidden' energy state transitions in quantum mechanics. As these transitions occur very slowly in certain materials, absorbed radiation is re-emitted at a lower intensity for up to several hours after the original excitation. Everyday examples of phosphorescent materials are the glow-in-the-dark toys, stickers, paint, wristwatch and clock dials that glow after being charged with a bright light such as in any normal reading or room light. Typically, the glow slowly fades out, sometimes within a few minutes or up to a few hours in a dark room. The study of phosphorescent materials led to the discovery of radioactivity in 1896.