Final answer:
Phosphorescents are substances that glow in the dark after being exposed to sunlight. They absorb photons and re-emit light over a longer period of time.
Step-by-step explanation:
Substances which will glow in the dark after being exposed to sunlight are called phosphorescents. Phosphorescence is a type of luminescence where a material absorbs photons and then re-emits them over a longer period of time. This delayed emission of light is what causes the substance to glow in the dark.