Fluorescence

1. Fluorescence is the visible or invisible radiation produced from certain substances as a result of incident radiation of a shorter wavelength such as X-rays or ultraviolet light.
2. Fluorescence, a type of luminescence, occurs in gas, liquid or solid chemical systems.

Fluorescence is brought about by absorption of photons in the singlet ground state promoted to a singlet excited state. The spin of the electron is still paired with the ground state electron, unlike phosphorescence. As the excited molecule returns to ground state, it involves the emission of a photon of lower energy, which corresponds to a longer wavelength, than the absorbed photon. Fluorescence has many practical applications, including mineralogy, gemology, medicine, chemical sensors (fluorescence spectroscopy), fluorescent labelling, dyes, biological detectors, cosmic-ray detection, vacuum fluorescent displays, and cathode-ray tubes.

Sources:

Прикладна фізика. Українсько-російсько-англійський тлумачний словник: У 4 т., Т. 4: С — Я / уклад.: О. Т. Богорош, С. О. Воронов, О. Г. Шайко-Шайковський, В. З. Маїк, М. Ф. Ясінський. — Львів : Укр. акад. друкарства, 2015. 786с.s

Britannica https://www.britannica.com/science/