Phosphor is a chemical substance that emits light when it is exposed to radiation, such as ultraviolet light. Some of the synonyms for this word include luminescent material, light-emitting substance, radioluminescent material, and fluorescent substance. These terms are often used interchangeably to refer to materials that emit light in different ways. Luminescent material highlights a broad range of phosphors, including those that produce light through chemical reactions or by direct excitation. Light-emitting substances, on the other hand, specifically refers to those materials that produce light through exposure to radiation. Whatever the term used, phosphors are an essential component of many modern technologies, from lighting and display screens to radiation detectors and medical imaging.