fluorescence v. phosphorescence
Friday, February 26, 2010 
Fluorescent scorpion. Image courtesy of The Firefly Forest. Fluorescence occurs when a substance absorbs radiation of one wavelength, and immediately emits radiation of a different wavelength. For example, whitening agents in laundry detergent make clothing mildly fluorescent. When laundered garments are exposed to the invisible ultraviolet radiation in sunlight, they re-emit longer wavelength visible light toward the blue end of the spectrum, making them appear whiter and brighter. Fluorescence also plays an important role in fluorescent lighting, biochemistry, and forensics.
Phosphorescence is a related type of photoluminescence in which absorbed radiation is re-emitted more slowly, so phosphorescent objects can still glow for periods up to several hours after the source of incident radiation is removed. Glow in the dark safety signs and toys may contain strontium oxide aluminate, a phosphorescent pigment.