What phenomenon describes the emission of visible light when a material is exposed to ultraviolet radiation?

Fluorescence is the phenomenon where a material absorbs ultraviolet (UV) radiation and then re-emits that energy as visible light almost instantaneously. This process occurs because certain substances have electrons that can be excited to a higher energy state when exposed to UV light. As these excited electrons return to their original state, they release energy in the form of visible light, which can often be of a different color than the absorbed radiation.

This characteristic is commonly observed in various minerals and gemstones, making fluorescence an important consideration in gemstone identification and appraisal. Notably, some gemstones exhibit strong fluorescence, which can enhance their visual appeal and market value.

In contrast, other phenomena such as refraction refers to the bending of light as it passes through different media, phosphorescence involves a delayed re-emission of light, and incandescence pertains to light produced by heat. These phenomena do not directly relate to the immediate emission of visible light upon exposure to UV radiation, distinguishing fluorescence as the correct answer in this context.