Final answer:
Fluorescent materials emit light when exposed to electromagnetic radiation by absorbing energy and emitting photons of lower energy and frequency.
Step-by-step explanation:
The substances that emit light when exposed to electromagnetic radiation are fluorescent materials. Certain fluorescent dyes, for instance, absorb ultraviolet or blue light and then emit photons of a different color, giving off visible light. This occurs because when electrons in the material jump to higher energy states upon absorbing energy, they almost immediately fall back down to their ground states, emitting photons of lower energy and frequency.