Phosphorescent compounds are materials that can absorb energy and re-emit it as light over an extended period. Unlike fluorescent materials, which emit light only while exposed to a light source, phosphorescent compounds continue to glow even after the light source is removed. This property is due to the unique electronic structure of the compounds, which allows them to store energy temporarily. Common examples of phosphorescent compounds include zinc sulfide and strontium aluminate. These materials are often used in glow-in-the-dark products, such as toys, watch dials, and emergency signs. Their ability to emit light in the dark makes them useful for safety and decorative applications.