Luminescence is a phenomenon where a material emits light without the need for external sources of light, such as when a substance absorbs energy and then re-emits it as light. This field of research covers various types of luminescence, including fluorescence, phosphorescence, and bioluminescence. Luminescent materials are commonly used in a wide range of applications, such as in lighting, displays, medical imaging, and security features. Researchers in this area study the properties and behavior of luminescent materials, as well as develop new materials and technologies for practical applications.